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Refractories in vacuum induction melting Da Costa e Silva, Andre Luiz V. 1979

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REFRACTORIES  IN VACUUM I N D U C T I O N  MELTING  by  Eng.  A n d r e L u i z V. da C o s t a e S i l v a M e t . , I n s t i t u t o M i l i t a r de E n g e n h a r i a , B r a s i l , 1 9 7 6  A T H E S I S S U B M I T T E D IN P A R T I A L F U L F I L L M E N T OF T H E R E Q U I R E M E N T S FOR THE D E G R E E OF M A S T E R OF A P P L I E D S C I E N C E  in THE F A C U L T Y OF G R A D U A T E S T U D I E S Department of M e t a l l u r g i c a l Engineering  We a c c e p t t h i s t h e s i s a s c o n f o r m i n g to t h e r e q u i r e d s t a n d a r d  T H E U N I V E R S I T Y OF B R I T I S H March,  COLUMBIA  1979  © A n d r e * L u i z V. da C o s t a e S i l v a , 1 9 7 9  In p r e s e n t i n g  this thesis i n p a r t i a l f u l f i l m e n t o f the requirements f o r  an advanced d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree that permission  f o r extensive copying o f t h i s t h e s i s  f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e s .  I t i s understood that copying o r p u b l i c a t i o n  of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my written  permission.  Department  nf  Metallurgical  Engineering  The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5  D  a  t  e  March 20,  1979  \  ABSTRACT The  l i t e r a t u r e i n Vacuum I n d u c t i o n  reviewed, with  especial  refractory-metal  lining  superalloy  Since  i t was  with  attack  in large on  j o i n t s , t e s t s were p e r f o r m e d to c h a r a c t e r i z e  the  was  s h o w n t o be  to metal a t t a c k . diffusion  of the  less stable oxides  in the c o r r o s i o n  process.  high  i n t e r a c t i o n b e t w e e n o x y g e n and  may  be  In t h e c a s e  (SiO^,  the  content  as f l u x e s was  of the  In o r d e r  attempted.  properties  To v e r i f y t h e mechanisms observed industrial  of s t e e l s ,  of s u p e r a l l o y s ,  the e l e m e n t s p r e s e n t  The  the  fluorides  performed  of  t e s t s , samples  Vacuum F u r n a c e s were e x a m i n e d .  I t was  of very  and  concerned.  p r o p o s e d i n the  ii  of  a  adherence to b r i c k s  v a l i d i t y (on a l a r g e s c a l e )  and  the  dissolution  use  c e m e n t s so p r o d u c e d  to a t t a c k ,  were  of  the  in  to produce cements with  l o w - s t a b i l i t y oxides,  w e l l , as f a r a s r e s i s t a n c e technological  resistance  rate c o n t r o l l i n g  oxygen a c t i v i t y in the m e l t , hence e n h a n c i n g the  small  P^O^,...)  c a u s e s an e x t r e m e d e p r e s s i o n  refractory oxides.  and  standpoint.  t h a t i n the case  step  all  cement  f o r the c e m e n t s low  It i s suggested  the a l l o y ( T i , A l , Cr)  furnaces  1  the main reason  that  this attack  d e t e r m i n e the most s u i t a b l e cements from t h i s presence of l o w - s t a b i l i t y oxides  and  determined  vacuum m e l t i n g  f a i l u r e s are a s s o c i a t e d  The  is briefly  e m p h a s i s on r e f r a c t o r y p r a c t i c e s  interactions.  i n b o t h s t e e l and  Melting  the from  concluded  t h a t t h e p r o c e s s e s . o c c u r r i n g i n a 1 a r g e f u r n a c e c a n be i z e d based on t h e n e e d  on t h e t e s t o b s e r v a t i o n s . f o r improved  rational-  A l s o c o m m e n t s w e r e made  pouring f a c i l i t i e s ,  i f the  products  o f t h e m e t a l - r e f r a c t o r y i n t e r a c t i o n a r e t o be k e p t o u t o f final  material produced.  This i s because  i n the  present  s t a t e o f the r e f r a c t o r y t e c h n o l o g y and p r a c t i c e , t h e s e actions  cannot  be  avoided.  the  inter-  T A B L E OF C O N T E N T S Page Abstract Table  i i  of Contents  List  of Tables  List  of Figures  iv vi vii  Acknowledgements  '  x  CHAPTER 1. I N T R O D U C T I O N  1  1.1 I n t r o d u c t i on  1  1.2 L i t e r a t u r e S u r v e y 1.2.1 Meta1 - R e f r a c t o r y Interactions Under Vacuum 1. 2 . 1 . 1 V a p o r i z a t i on 1.2.1.2 D i s s o l u t i o n o f R e f r a c t o r i e s 1.2.1.3 R e a c t i o n w i t h A l l o y i n g E l e m e n t s 1.2.1.3.1 Carbon 1.2.1.3.2 O t h e r A l l o y i n g E l e m e n t s 1.2.1.4 E f f e c t o f M i n o r Components 1.2.1.5 K i n e t i c A s p e c t s 1.2.2 R e f r a c t o r y P r a c t i c e i n V I M 1.2.3 O t h e r R e a c t i o n s W i t h t h e L i n i n g  4  10 12 14 20  1.3 O b j e c t i v e s  24  o f the Research Project  4 4 4 5  2. E X P E R I M E N T A L  25  3. R E S U L T S  29  3.1 T e s t s U s i n g A I S I 1 0 9 5 S t e e l 3.1.1 M u l l i t e B a s e d Cement 3.1.2 C e m e n t s W i t h 1 0 % S i l i c a iv  29 29 31  Page 3.1.3 3.1.4 3.1.5 3.1.6 3.2  Cements Produced Using F l u o r i d e s Low S i l i c a P h o s p h a t e B o n d e d C e m e n t S i l i c a C o n t a i n i n g Phosphate Bonded Cement Summary o f S t e e l T e s t s  Tests Using  4. O B S E R V A T I O N OF  X-750 S u p e r a l l o y  42  INDUSTRIAL SAMPLES  50  4.1 4.2  S l a g From D e s u l p h u r i z a t i o n T r e a t m e n t Magnel B r i c k 4.2.1 M a c r o s c o p i c O b s e r v a t i o n 4.2.2 M i c r o s c o p i c O b s e r v a t i o n 4.3 I n c l u s i o n s i n N i - B a s e d S u p e r a l l o y 4.4 P i e c e o f Rammed L i n i n g 4.4.1 M a c r o s c o p i c O b s e r v a t i o n 4.4.2  Microscopic  5. C O N C L U S I O N S AND  32 36 38 40  50 52 52 52 56 58 58  Observation  58  RECOMMENDATIONS  61  BIBLIOGRAPHY  67  v  L I S T OF  TABLES Page  1. 2. 3.  S o l u b i l i t y product of various oxides in Iron and N i c k e l  121  P r e s s u r e s o f CO i n e q u i l i b r i u m w i t h d i f f e r e n t o x i d e s and s t e e l melts  121  Nominal composition  o f some  Vacuum  Melted Superalloys  122  4.  Refractory Practices  123  5.  Composition  of metals  6.  Composition  of Refractories tested  7.  O x y g e n c o n t e n t o f X - 7 5 0 a f t e r 15 m i n . h o l d i n g time i n d i f f e r e n t c r u c i b l e s  used  vi  i n the t e s t s  129 130 13:1  L I S T OF F I G U R E S 1.  Theoretical  2.  Deoxidation curves  3.  Dimensions  4.  Different wetting behaviours  77  5.  Experimental Apparatus  78  6.  V a r i a t i o n i n carbon c o n t e n t o f AISI melted i n Tasil-X crucibles  7.  Interface  8. 9. 10.  deoxidation  Page 74  diagram  75  o f the crucibles  AISI  used i n the t e s t s  1095 s t e e l 79  1095/Tasil-X  80  Microstructure  of Taylor  81  Interface  1 0 9 5 / A l u n d u m 1162  AISI  Typical microstructure A 1 0 and CaF (CAF) 2  3  320  82  o f a c e m e n t made  from 83  2  11.  Adherence test.  12.  V a r i a t i o n i n carbon c o n t e n t o f AISI m e l t e d i n CAF c r u c i b l e s  1095 s t e e l  V a r i a t i o n i n carbon c o n t e n t o f AISI m e l t e d i n Alundum 1139 c r u c i b l e s  1095 s t e e l  13. 14.  Interface  Typical microstructure A l 0 a n d MgF,, ( S P 2 ) 2  15.  76  Magnel/CAF  84 85 86  o f a c e m e n t made  from 87  3  V a r i a t i o n i n carbon c o n t e n t o f AISI m e l t e d i n SP2 c r u c i b l e s  16.  Adherence t e s t .  17.  V a r i a t i o n i n carbon c o n t e n t o f AISI m e l t e d i n T a y l o r 341 c r u c i b l e s AISI  Interface  1095 s t e e l 88  Magnel/SP2.  89  1095 s t e e l 90  18.  Interface  1 0 9 5 / T a y l o r 341  91  19.  V a r i a t i o n i n c a r b o n c o n t e n t o f AISI 1095 s t e e l m e l t e d i n C o r a l b o n d and T a s i l - X c r u c i b l e s as a f u n c t i o n o f th vii  92  Page 20.  Interface  AISI  1095/Cora1 bond  21.  Detail of altered Coralbond  22.  Alumina  i n c l u s i o n s from  Interface  AISI  93 94  Coralbond.  1095/Coralbond  23.  Equilibrium  24.  Interface  X-750/Magnel  25.  Interface  X-750/Magnel , metal  26.  Deoxidation  27. 28.  D e n s e l a y e r f o r m e d a t i n t e r f a c e X - 7 5 0 / T a y l o r 341 M i c r o s t r u c t u r e of s l a g from d e s u l p h u r i z a t i o n treatment  101  Microstructure treatment  102  29.  A1 0  95  2  3  = 2A_1 + 30 i n N i c k e l  equilibria  97  of s l a g from  Used Magnel  31.  Cross section of working Magnel b r i c k  33.  34.  98 99  Metal penetration Ca1cium-Aluminate and Z i r c o n i u m  103 face  of 104 brick 105  i n Magnel b r i c k . containing Titanium  Detail of a periclase grain  ' in  brick  107  P e r i c l a s e g r a i n i n used Magnel  36.  C a l c i u m - A l u m i n a t e s on t h e w o r k i n g  brick  108  face  of Magnel l a y e r on t h e w o r k i n g  106  unused  35.  109  37.  Spinel  38.  Macroinc1 usions in p a r t i a l l y forged Ni-base superalloy Microstructure of Calcium-Aluminate i n c l u s i o n i n F i g . 38 vi i i  39.  100  desulphurization  brick  Metal p e n e t r a t i o n i n Magnel via Ca1cium-Aluminates  Magnel  removed  i n a N i - 1 % A1 a l l o y  30.  32.  96  f a c e o f Magnel  110 111 112  Page 40.  Microstructure partially  of spinel inclusion in  forged Ni-base alloy  41.  Piece  42.  Typical microstructure  113  o f u s e d rammed l i n i n g o f t h e rammed  114 lining,  60mm f r o m t h e w o r k i n g f a c e  115  43.  Cross-section  116  44.  Inclusions  45.  A l t e r e d r a m m e d l i n i n g 5mm f r o m t h e w o r k i n g face U n a l t e r e d MgO g r a i n c l o s e t o t h e w o r k i n g f a c e o f t h e rammed l i n i n g  46.  of working  f a c e o f rammed l i n i n g  f r o m rammed l i n i n g  ix  117 118 119  ACKNOWLEDGEMENTS The  author  would l i k e to express  Dr. A l e c M i t c h e l l , f o r h i s h e l p and course  of t h i s work.  colleagues  i n the  Much a p p r e c i a t i o n with  The  is given  fellow students  and  of several  f o r t h e i r h e l p f u l c r i t i c i s m of the  his  discussions  f a c u l t y members. Chacklader  of  the  gratifying.  f o r t h e many h e l p f u l  other  to  throughout  been extremely  w o u l d a l s o l i k e t o t h a n k Dr. A . C D . Ballantyne,  guidance  cooperation  i n d u s t r y has  his gratitude  The and  Dr.  author A.S.  d r a f t manu-  script. The A g e n c y and  support  of the Canadian  o f t h e M i n i s t e r i o da  International  Development  I n d u s t r i a e Come'rcio,  Brasil,  are g r a t e f u l l y acknowledged. Special for t h e i r support  t h a n k s a r e due during  to E l e c t r o m e t a l  this project.  x  Acos f i n o s  S.A.,  1  CHAPTER 1 INTRODUCTION 1. 1  Introduction With the  for  the a e r o s p a c e ,  industries, important now  i n c r e a s i n g demand f o r h i g h q u a l i t y m a t e r i a l s n u c l e a r and  Vacuum I n d u c t i o n  Melting  p o s i t i o n a s an a l l o y - m a k i n g  well understood  it i s very process  other highly sophisticated  likely  contamination  has  reached  process.  Due  and c o n t r o l l e d t e c h n o l o g i c a l that i t will  f o r some c o n s i d e r a b l e The  (VIM)  time  much l e s s c o n t a m i n a t i n g  one  than  i n t o the  advantages primary  future.  a t m o s p h e r e as a s o u r c e  and even a m e d i o c r e  a very pure  gas.  of  vacuum i s  One  must  aware, however, of the e f f e c t s of the v a r i o u s p r e s s u r e tive  very  to i t s  k e e p i t s p o s i t i o n as a  idea of removing the i s n o t a new  a  be sensi-  r e a c t i o n s o c c u r r i n g in s t e e l or high-temperature  alloy-  making. Induction  heating i s , without  q u e s t i o n , one  of  the  c l e a n e s t and e a s i e s t t o c o n t r o l h e a t i n g methods a v a i l a b l e , offering  "con t a c t l e s s " h e a t i n g w i t h  t u r e c o n t r o l and reduced  o r no p r o b l e m  of  in operating  tempera-  under  pressures. S i n c e we  for  little  a high degree  very expensive  are d e a l i n g with  a primary  melting  alloys, i t is clear that a  process  continuous  2  process i s not f e a s i b l e . bringing  Batch o p e r a t i o n i s then  i n t o the s i t u a t i o n  the need  necessary,  for a container.  c o n t a i n e r s h o u l d be a b l e t o r e s i s t t h e t e m p e r a t u r e s molten  metals  and,  within  a reasonable  This  of  the  a t t h e same t i m e , k e e p t h e h e a t l o s s e s level.  It is also clear that  the  c o n t a i n e r s h o u l d i n t e r a c t to the minimum e x t e n t p o s s i b l e w i t h the m e t a l .  Although  t h e two  first  d e m a n d s a r e f u l f i l l e d by  s e r i e s o f c o n v e n t i o n a l r e f r a c t o r y m a t e r i a l s , the l a s t poses  the b i g g e s t d i f f i c u l t y ,  Even refractories  to  though  are u s u a l l y  utilize.  non-oxide  f o r VIM  m a t e r i a l s have been  used  as  f u r n a c e s , most o f the p o t e n t i a l c a n d i -  dates amongst these m a t e r i a l s f i n d severe economic What i s t h e n s e e n  one  r e d u c i n g the number of p o s s i b l e  a t e r n a t i v e s to a handful of m a t e r i a l s which expensive and.hard  a  limitation.  i s t h e e x t e n s i v e use o f o x i d e s o r  mixtures  o f o x i d e s i n t h e f o r m o f p r e f i r e d , o r rammed i n p l a c e , o r brick/cement  lining  ature Nickel-based  as c o n t a i n e r s f o r s t e e l s a n d h i g h alloys.  To a g g r a v a t e  the chemical  o f t h e a l l o y s made by VIM reactive  alloying  interaction  contain relatively  a t l o w e r p r e s s u r e s due +  problem,  most  l a r g e amounts  a d d i t i v e s s u c h as T i , A l , e t c . , o r , i n  case of s t e e l , carbon, the l a t t e r becoming  •C  temper-  0  =  of  the  much m o r e r e a c t i v e  to the e f f e c t of r e a c t i o n CO  (g) .  In a d d i t i o n , h i g h q u a l i t y m a t e r i a l s r e q u i r e h i g h heat-to-heat reproducibility ability  i n p r o p e r t i e s , maximum  ( s i n c e they a r e , per se, hard to work) and,  hot-workin  the  3  case of h e a t - r e s i s t i n g All  alloys, excellent  these c h a r a c t e r i s t i c s are influenced  element contamination from r e f r a c t o r y  no d i s s o l u t i o n ) a refractory.  achieved. extent  Recognition part  i f the best  Refractories  stability  (no  desired in  i n the r e f i n i n g process  becomes  vacuum m e l t i n g  i s t o be  practice  be a t t a c k e d  processed  thoroughly  r e f r a c t o r y / a 11oy  reaction-  t h a t t h e r e f r a c t o r i e s a r e one o f  should  by t h e a l l o y s b e i n g  best  trace  products  as one o f t h e p a r a m o u n t p r o p e r t i e s  unavoidable reaction the  g r e a t l y by  interaction.  components taking  then e s s e n t i a l  properties.  and i n c l u s i o n s , both l i k e l y  In V I M , o n e t h e n s e e s c h e m i c a l  the  creep  t o a minimum  and t h e p r o d u c t o f any  defined  combinations.  i n order  to  achieve  1.2  Literature 1.2.1  Survey  Metal-Refractory 1.2.1.1  Although definite  secondary  Under  Vacuum  V a p o r i z a t i on  vaporization  possibility  extensively  Interactions  of r e f r a c t o r y  (1), this  i n the p r e s e n t  importance,  problem w i l l  study  since  i t is  oxides  is a  n o t be d e a l t w i t h likely  compared t o d i r e c t c h e m i c a l  t o be o f  a t t a c k by  the m e l t . 1.2.1.2  Dissolution  The s i m p l e s t  process  that  oxide  which  X and oxygen a r e s o l u b l e  the  in contact with  of  a metal Y, in  to a certain extent,  is  AG,  (1)  dissolution XO = X This  and,  Refractories  can o c c u r when a p i e c e  refractory both  XO i s b r o u g h t  of  given  given  + 0  i n Y  i n Y  reaction w i l l  occur at the m e t a l - o x i d e  s u f f i c i e n t time, achieve  the s o l u b i l i t y  interface limit  by t h e p r o d u c t h  When-h  and h  - .  x o  and a  x Q  A  Q  e-".>"  (2)  a r e t h e a c t i v i t i e s o f X, fj and XO,  respectively. Table of oxides most  1 presents  in iron  a t 1600°C  of the d i s s o l u t i o n  pressure  sensitive,  thermodynamics  the s o l u b i l i t y p r o d u c t s and a t m o s p h e r i c  processes  pressure.  l i s t e d in Table  one can use them a g u i d e l i n e s  o f the d i s s o l u t i o n  process.  for a series Since  1 are not f o r the  5 S h o u l d X be h i g h l y v o l a t i l e a n d i n s o l u b l e ( o r a l m o s t ) , s u c h as Mg o r Ca i n i r o n , t h e d i s s o l u t i o n w i l l saturation  of the bath w i t h oxygen  f o r m a t i o n o f a FeO at  s l a g , due  the metal/vacuum MgO  (5).  proceed  This will  to  l e a d to the  t o t h e e v a p o r a t i o n o f Mg  (or  Ca)  i n t e r f a c e , d i s p l a c i n g the r e a c t i o n  = Mg + 0  by t h e c o n s t a n t r e m o v a l  o f one  o f the p r o d u c t s .  be o b s e r v e d , h o w e v e r , w h e n t h e p r o c e s s k i n e t i c s  T h i s may are  not  very  sluggish. All they w i l l  these p r o c e s s e s are o b v i o u s l y u n d e s i r a b l e s i n c e  i n t r o d u c e an u n a c c o u n t e d  a l l o y i n g element  o x i d i z e the b a t h , most p r o b a b l y c o m p r o m i s i n g of the r e s u l t i n g  Reaction With A l l o y i n g 1.2.1.3.1  elements  above  are p r e s e n t .  has been  a steady decrease  Elements  Carbon  p i c t u r e changes,  most i m p o r t a n t e l e m e n t confusion  the p r o p e r t i e s  alloy.  1.2.1.3  The  and  h o w e v e r , when  alloying  In t h e c a s e o f s t e e l s , c a r b o n  i s the  i n VIM  most  generated. in carbon  and t h e one  over which  Although a l l authors  c o n t e n t o f t h e a l l o y , as  observe the  r e a c t i on XO +  C  = CO + X  p r o c e e d s , a g r e a t d e a l o f m i s u n d e r s t a n d i n g has been about  by f a i l i n g t o a c k n o w l e d g e  the k i n e t i c a s p e c t s of the  p r o c e s s and t r y i n g to compare r e s u l t s different initial  carbon  brought  contents.  from s t e e l s with  The e x p e r i m e n t s  by  widely Bennett  6 e t a l . ( 6 ) , who s t a r t e d h i s t e s t s w i t h a ' 0 . 2 % C s t e e l crucible  a n d o b s e r v e d r e a c t i o n t i m e s o f up t o 85  showed the achievement about  8 ppm.  o f a c l e a r minimum  This i s in obvious  steel  c o n t e n t , somewhere  10 ppm.  has b e e n - f o u n d " ,  ( 7 ) , who  minimum  Although Oberg  p o i n t o u t t h a t "no w o r k c o v e r i n g a w i d e r r a n g e concentration  level, of  c o n f l i c t as t h e a u t h o r s  and o b s e r v e d a peaked above  minutes,  oxygen  p o i n t o u t , w i t h t h e p r e v i o u s r e s u l t s o f Moore w i t h a 0.1%C  i n a MgO  started  i n the  et al.(8)  o f carbon  the k i n e t i c study o f Machlin  ( 9 ) h a s s h o w n w h a t s h o u l d be e x p e c t e d i n s u c h a c a s e . s t a r t s with a high carbon  oxygen  I f one  a c t i v i t y melt, the d i s s o l u t i o n  step  MgO = Mg. + 0 and t h e d e o x i d a t i o n s t e p C + 0 = CO will  define a kinetic equilibrium fixing  oxygen  level  in the bath.  As t h e c a r b o n  during this p e r i o d , the steep ascendent equilibrium hyperbole will the " f r e e oxygen  a steady-state c o n t e n t goes  down  s i d e o f t h e C/0  be r e a c h e d a n d w h a t O b e r g  uptake" w i l l  prevail.  T h i s whole  called  p r o c e s s can  be d e s c r i b e d b y a c u r v e a s F i g . 1, w h e r e o n e o b s e r v e s an : initial oxygen  d e o x i d a t i o n , then a s t e a d y - s t a t e and f i n a l l y a c o n t e n t i n c r e a s e , due t o t h e l a c k o f s u f f i c i e n t  flushing.  I t i s easy t o u n d e r s t a n d t h a t what Moore  a c t u a l l y , was j u s t  an o v e r l a p p i n g o f b o t h  p r o c e s s e s , d u e t o an i n j u d i c i o u s s e l e c t i o n  fast CO  observed,  unsteady-state of carbon  content.  7  The  understanding  paramount importance  f o r the o p e r a t i o n  it will  permit  the best  content  t o be  reached.  Since s t a t e and o f the  of t h i s process  deoxidation  o f VIM  and  consumption  furnaces,  since  the minimum i n c l u s i o n  the minimum oxygen c o n t e n t  the carbon  i s c l e a r l y of  a t t a i n e d at  rate are both  steady-  direct  functions  dissociation reaction XO - X + 0  it is evident criteria in  that those  two  conditions will  be  for assessment of r e f r a c t o r y s t a b i l i t y  adequate and  adequacy  VIM. Schaffer  dynamics of the With e x t e n s i v e bath, the  (10)  and  various  others  have c a l c u l a t e d the  melt-refractory  s i m p l i f i c a t i o n s he  c o n t a i n i n g 0.4%C  reactions  found  thermo-  possible.  t h a t , f o r an  the e q u i l i b r i u m pressures  iron  o f CO  for  reaction X0 + C = CO + X  w o u l d be as g i v e n usual  operating  expect  the from  take  in account  prevail there  pressures  reduction  able  2.  in Table  As t h e y  o f VIM  of the  furnaces  only  (80y),  f a c t that these  H o w e v e r one re 1 a t i o n s h i p s  the  should favour-  should  also  shou1d  f o r the m e t a l - c r u c i b l e - v a c u u m i n t e r f a c e , where  i s no n u c l e a t i o n  b a r r i e r f o r CO  formation.  d e e p e r i n t h e me 1 1 - c r u c i b l e i n t e r f a c e , t h e C/0 t i on m u s t be s u f f i c i e n t t o o v e r c o m e t h e the s u r f a c e  one  r e f r a c t o r i e s t o be h i g h l y  a thermodynamic viewpoint. the  are a l l w e l l over  forces  (CO  n u c l e a t i n g then  As o n e  goes  supersatura-  f e r r o s t a t i c head as b u b b l e s )  and  otherwise  8  the a t t a c k has to proceed  as d i s s o l u t i o n o f the o x i d e ,  ( e n h a n c e d b y t h e l o w fJ c o n t e n t of 0 through  the bath  of a C rich bath),  a n d CO f o r m a t i o n  transport  and d e s o r p t i o n  at the  s urface . Turillon  (11) and o t h e r s  tion of iron melts and  recognized  reaction. F i g . 2.  have s t u d i e d t h e d e o x i d a -  under Vacuum I n d u c t i o n  the importance  He o b s e r v e d  Melting  of the r e f r a c t o r y  the behaviour  conditions decomposition  p r e d i c t e d by M a c h l i n , i n  T u r i l l o n also noticed that, i n h i s MgO/spinel  c r u c i b l e s , a t t h e p o i n t o f m i n i m u m C^ a n d 0_ c o n c e n t r a t i o n preceding  the " f r e e oxygen uptake", the d e o x i d a t i o n  refractory decomposition  rates, determined  were e q u a l , w i t h a value  of approximately  and t h e  independently, 1.5 ppm 0 / m i n .  A c o n s i d e r a b l e n u m b e r o f s t u d i e s h a v e a l s o b e e n made taking i n account  the carbon  boil  conditions, i.e., critical  crevice sizes f o r nucleation of bubbles, needed, e t c . Besides  the conventional  supersaturation treatment  o f Darken  ( 1 2 ) , K r a u s ( 1 3 ) h a s c a l c u l a t e d t h e c h a r a c t e r i s t i c s o f CO bubbles  i n vacuum carbon  deoxidation.  He p r e s e n t e d  bubble  c h a r a c t e r i s t i c s g r a p h i c s , s h o w i n g t h e maximum a c t i v e d e p t h bubbling,  of  t h e minimum s u p e r s a t u r a t i o n needed f o r b u b b l e  n u c l e a t i o n , a n d t h e e f f e c t o f s e v e r a l o t h e r v a r i a b l e s on t h e degassing  processes.  He p o i n t e d o u t t h a t , i f t h e n u c l e a t i o n  frequency  as a f u n c t i o n o f p r e s s u r e  known, t h e r a t e o f d e g a s s i n g mined.  Unfortunately,  during  and c o n c e n t r a t i o n the boil  was  c o u l d be d e t e r -  as Kinsman e t a l . (14) p o i n t o u t , t h i s  knowledge i s not a v a i l a b l e and should  d e p e n d on s e v e r a l  hard  9 c h a r a c t e r i z e f a c t o r s such as a g i t a t i o n of the b a t h , c h a r a c t e r i s t i c s of the c r u c i b l e , presence  of  surface  heterogeneous  nuclei, etc. It boil  i s important  i s the major  substantial  to keep i n mind, t h a t , a l t h o u g h  CO e l i m i n a t i o n p r o c e s s , o n c e  oxygen  removal  still  the  i t subsides,  h a p p e n s by s u r f a c e  desorp-  tion. 1.2.1.3.2 Precipitation basically  Other Al l o y i n g  hardening nieke 1-based  on a l u m i n i u m - ,  and  achieve t h e i r high temperature uncommon t o f i n d a l l o y s w i t h  Elements alloys  rely  t i t an i u r n - r i ch p r e c i p i t a t e s t o strength (15). up t o 4 - 5 %  I t i s not  Ti+Al  (Table 3).  A  will  show t h a t  both  \  b r i e f l o o k a t an o x i d e s t a b i 1 i t y A1^0^  and TiOg  a r e among t h e most s t a b l e o x i d e s .  elements  will  Although  vacuum w i l l  present then, r e a c t i v i t y problems  tions, i t is still main d r i v i n g  n o t l i k e l y p l a y any  important  Zr,  of ceramics  ( 1 6 , 17,  18)  role in these  reac-  of the  i s the p o s s i b i l i t y  of  have s t u d i e d the  by N i c k e l a l l o y s .  rapid wetting of refractories  Al , T i and  with crucibles.  rich in reactive elements.  Various authors  observed  These  t o s t u d y t h e m s i n c e one  f o r c e s f o r t h e u s e o f VIM  producing alloys  wettability  diagram  C, a n d  Sutton  (19)  by a l l o y s c o n t a i n i n g  found t h a t w e t t i n g i n c r e a s e d with  content of the a l l o y i n g a d d i t i o n .  Snape (20) o b s e r v e d  t h e w e t t a b i l i t y o r d e r o f v a r i o u s a l l o y s i s t h e same i n ent r e f r a c t o r i e s s u b s t r a t e s . wetting of alumina  He  the that differ-  a l s o n o t i c e d the i n c r e a s e d  c r u c i b l e s by r e a c t i v e a 1 1 o y i n g  elements  in  10 a l a r g e number o f commercial nieke 1 -carbon  high temperature  and  alloys.  The p r o c e s s i n q u e s t i o n , f o r a N i - T i Alumina  alloys  c r u c i b l e , would  a l l o y in a pure  be d e s c r i b e d by  f-T_i + A l „ 0 _ = J-Ti0 . 9  t.  + 2AJ_ A1 0 2  3  It i s c l e a r t h a t the aluminum  content of the bath  play a r o l e i n the e q u i l i b r i u m . S u t t o n found s t r o n g in w e t t a b i l i t y dissolution  depending  o f the Ti0£  activity will  on t h e T i / A l formed  r a t i o i n the a l l o y .  made by S n a p e ,  K a m a m u r a e t a l . ( 2 2 ) who  An e x t e n s i v e s t u d y  G u p t a e t a 1. ( 2 1 )  noted the a l t e r a t i o n  r e f r a c t o r y s u b s u r f a c e l a y e r s and e n r i c h m e n t s  E f f e c t of Minor  use o f pure s i l i c a  contact with either steel  and  s u f f e r e d by in Cr, Ti  the  and  Components  refractories  o r n i e k e 1-a 1 1 o y s  r u l e d o u t due t o t h e low s t a b i l i t y  under vacuum i n s h o u l d be  vast number o f commercial  clearly  of SiO^ in presence of C  a t low p r e s s u r e s , o r o f A l , T i a l l o y i n g e l e m e n t s . refractories  in which  an i m p o r t a n t r o l e as a b i n d i n g a g e n t - - s u c h  tion  of  elements.  1.2.1.4  aluminous  The  i n t h e c r u c i b l e and i t s f i n a l  i n c r e a s i n g the e r o s i o n .  t h o s e r e a c t i o n s was  The  variations  be i m p o r t a n t i n t h i s p r o c e s s - - a l a r g e s o l u b i l i t y  in the c r u c i b l e  other alloying  will  But,  silica  as m u l l i t e ,  the plays silico-  and h i g h - a 1 u m i n a - - h a s p r e c l u d e d i t s c o m p l e t e e l i m i n a -  from the vacuum i n d u c t i o n m e l t i n g scene.  o f s i l i c a and i t s p r e s e n c e i n most ores pose  The  abundance  economical  11 problems in making r e f r a c t o r i e s with Fe^Og i s a l s o o f t e n p r e s e n t  very  as i m p u r i t y  l o w - s i l i c a content.  (23), i t s removal  b e i n g e c o n omi c a l l y un f e a s i b l e . The increased  work o f Graham e t a l . ( 2 4 ) i n t e r a c t i o n t o be e x p e c t e d  shows c l e a r l y the as t h e  silica  content  of  s i ' l i c o - a , l umi n o u s r e f r a c t o r i e s i s i n c r e a s e d .  Machlin  estimated  a 10  content  of a  fold  steel  increase  melted  Hoffmann.  in the steady-state  i n a 1% S i 0 ^ - M g O c r u c i b l e , u s e d Although  some s u g g e s t  able to consume the s i l i c a silica  reduction  t o r y , one  oxygen  t o be  possible decrease  in the working  the  Fisher  t h a t a wash heat  c o n t r o l l e d by  must c o n s i d e r  by  should  i n p o r o s i t y and  i n s t r e n g t h • a-ssoci ated'Wi th the  Most l i k e l y ,  wetted  altered layer will  s p a l l when t h e  residual  (23)  dissolved in  next  heat,  as t h e  explanation reducing  (25)  who  observed  a i r d r i e d a t 2 2 5 ° C and  same c a r b o n  consumption  then  wash-heat.  and  gases  i n r e f r a c t o r i e s can  in  alloys.  They t h e r e f o r e  the  better  crucibles is  given  vacuum d r i e d produced  the  s t e e l as a c r u c i b l e  This would i n d i c a t e that absorbed  Snape a l s o r e p o r t e d content  be m a j o r s o u r c e s  of  purposes  at  ( c r u c i b l e s o f 206  i n c r e a s e d w e t t a b i l i t y due  (although  water  oxidation  r e c o m m e n d e d an a i r d r y i n g  h. f o r r e s e a r c h  increased silica  metal,  that a c r u c i b l e which  i n the molten  a f t e r one  1 2 5 0 ° C f o r 24  A much  this  favorable e f f e c t s of a "wash-heat" in  " p o l l u t i o n " p o t e n t i a l of the  by H u n t e r & T a r b y was  b i n d i n g phase i s absent.  f o r the  the  a n d / o r be  refrac-  corrosion  intergranu1 ar s i 1 i c o - a l u m i n a t e s .  solidifies  the  the  of the  a f t e r teeming,  be  face, causing  d i f f u s i o n i n the  increase  and  cm  to  some i n c r e a s e i n p o r o s i t y  ).  12 was  also  experimented). As b o r o n  oxide  o t h e r o x i d e s , i t has a d d i t i on s - - a s  refractories  ties.  and  several  of b o r i c a c i d  bonds f o r v a r i o u s a p p l i c a t i o n s .  et a l . ( 2 6 ) showed, a l l o y s produced  c o n t a i n i n g 1.2%  B  2^3  in  cannot  which  hot w o r k a b i l i t y  In t h e c a s e o f h i g h q u a l i t y m a t e r i a l s i n w h i c h i s mandatory, the d i f f e r e n t l e v e l s of  t i o n s d u r i n g the l i f e  properrepro-  contamina-  o f t h e c r u c i b l e r e p o r t e d by D e c k e r  be t o l e r a t e d .  As W i n k l e r  (23) o b s e r v e s ,  stability  are used  during the manufacture  et  wetting  and e r o s i o n o f t h e c r u c i b l e a r e p r o m o t e d i f b i n d e r s o f chemical  MgO  c o n t a i n e d some b o r o n ,  f o r v a r i a t i o n s i n c r e e p and  ducibility  al.  f l u x t o MgO  been u s e d - - i n the form  chemical  H o w e v e r as D e c k e r  accounted  i s a powerful  of  lower the  c r u c i b l e , as t h e y a r e p r e f e r e n t i a l l y d e c o m p o s e d . 1.2.1.5 Although e x t e n s i v e and observed. mental  K i n e t i c Aspects  the thermodynamic p r e d i c t i o n s  v i o l e n t c o r r o s i o n , t h a t i s not what i s u s u a l l y  In a d d i t i o n , d i s c r e p a n c y  r e s u l t s from  accounted  d i f f e r e n t authors  It i s important  and  i s found between e x p e r i which  cannot  f o r s i m p l y by d i f f e r e n t e x p e r i m e n t a l  open and  be  techniques.  to keep i n mind t h a t f a c t o r s such  closed p o r o s i t y , mechanical  s i z e d i s t r i b u t i o n , temperature  agitation  suggest  r e s i s t a n ce , g r a i n s i z e of the t e s t , degree  (frequency of current, size of furnace, etc.)  play a definite  role in determining  the v a r i o u s r e f r a c t o r i e s .  as  of will  the r e a c t i o n k i n e t i c s f o r  13  Turillon  (27)  noticed  minimum oxygen c o n t e n t f u s e d MgO  they  mechanical transport  latter  resistance.  Machlin  can  lower thermal  assumed the  c o n t r o l l e d a t the c r u c i b l e / m e t a l  to pose l i m i t a t i o n s to the p r o c e s s .  i.e., depletion  a t the  c e r t a i n l y be e x p e c t e d  differential  influence  main  hardly  ing  place  by d i s c r e t e p i e c e s  is  most  variations the  mass  interface.  of  by  refractory  Once a p i e c e that i t will  The  i t s much i n c r e a s e d  area.  higher  the  obvious  phenomena,  helping  the  frequency,  hence, less erosion  o f r e f r a c t o r y has be  from i t s  rate of transport  of bond s o f t e n i n g , again  of refractory grains.  likely  It  bath.  in i n c r e a s i n g the  expected.  it  stabilities.  a p p e a r as e f f e c t s on  t h e a g i t a t i o n o f t h e m e l t and  very  occur,  t o be t r u e w h e n t h e r e  e f f e c t of temperature, apart  a l s o be one  be  metal/vacuum  as S n a p e o b s e r v e d , much o f t h e o x y g e n i n t a k e  The  will  to  phase i s the  corroded  t r a n s f e r c o e f f i c i e n t at the m e t a l / c r u c i b l e  i n t o the  and  may  interface will  not  in c r u c i b l e p a r a m e t e r s w i l l  falling  shock  Although this  reaction of phases of various  the metal takes  or  results,  reaction and  i s c l e a r t h a t f o r the purpose of m o d e l l i n g ,  Besides,  the  r e a c t i o n i t s e l f proceeded f a s t enough  be s o f o r c r u c i b l e s i n w h i c h t h e one,  in  g i v i n g the b e t t e r  have, unfortunately,  i n t e r f a c e s , i . e . , the not  differences  a t t a i n a b l e w h e n u s i n g r a m m e d MgO  c r u c i b l e s , the  although  sharp  loosenthe  i s to  lower be  been e r o d e d i t i s  d i s s o l v e d a t a f a s t r a t e due  to  14 1.2.2  R e f r a c t o r y P r a c t i c e i n VIM  Besides  the c l e a r importance  of the thermodynamic  s t a b i l i t y o f t h e l i n i n g m a t e r i a l , we h a v e s e e n actual  s t r u c t u r e o f the r e f r a c t o r y w i l l  in the k i n e t i c s o f the a t t a c k process.  that the  play a definite  role  I t i s then i n s t r u c t -  ive to study the d i f f e r e n t r e f r a c t o r y p r a c t i c e s applied i n VIM,  comparing Table  t h e i r advantages 4 presents  and drawbacks.  various p r a c t i c e s quoted  l i t e r a t u r e a n d t h e f o l l o w i n g c a n be Laboratory  furnaces  in the  observed.  and s m a l l f u r n a c e s  up t o a b o u t  25kg c a p a c i t y u s u a l l y employ p r e f i r e d c r u c i b l e s .  Although  i t w o u l d be p o s s i b l e t o u s e r a m m e d l i n i n g s , t h e l a b o u r  costs  a r e p r o h i b i t i v e . As t h e f u r n a c e s i z e i n c r e a s e s t h e l i m i t f o r prefired  c r u c i b l e s i s reached  l i n i n g becoming more e c o n o m i c a l  a t about  2 5 0 k g , t h e rammed  as t h i s v a l u e i s  approached  (51). F o r i r o n and n i c k e l m e l t i n g p u r p o s e s , r e l i e s on h i g h p u r i t y MgO (96%A1 0 , 2%Si0 ) 2  3  2  one u s u a l l y  (96%MgO, 2%Si 0 , l % F e 0 ) 2  (51), although  z i r c o n i a c r u c i b l e s c a n a l s o be  2  Mg0.Al 0 2  3  3  or A1 0 2  3  or stabilized  used.  As C h i l d e t a l . ( 5 1 ) p o i n t s o u t , h o w e v e r , p r e f i r e d crucibles are not considered f o r industrial to the high p r i c e and s h o r t l i f e s . more dangerous wide and cause  than  a p p l i c a t i o n s , due  B e s i d e s , c r a c k s a r e much  i n rammed c r u c i b l e s , s i n c e t h e y  can open  leakage.  Ramming m i x t u r e s  f o r Induction  by a n u m b e r o f m a n u f a c t u r e r s . h o w e v e r , when e x t e n d i n g  Care  Furnaces  are  produced  s h o u l d be e x e r c i s e d ,  t h e i r use t o Vacuum I n d u c t i o n  Melting.  15 High s i l i c a tion  linings  f o r i n s t a n c e , q u i t e common i n A i r  f u r n a c e s , m u s t be b a n n e d i f t h e b e s t r e f r a c t o r y p r a c t i c e  i s t o be a c h i e v e d .  The  Fe^O^  c o n t e n t m u s t a l s o be k e p t  a l t h o u g h i t i s an e x c e l l e n t a d d i t i v e t o p r o m o t e MgO due  Induc-  to i t s f 1 u x i n g a b i 1 i t y .  present  a  Winkler  (15) p r e f e r s to s e t the upper  low o x y g e n  l / U F ^ O ^ . MgO  Although  Child et a l .  c r u c i b l e as a t y p i c a l  low,  sintering, (51)  VIM m a t e r i a l ,  l i m i t at 0.5%Fe202> i f  l e v e l s a r e t o be a t t a i n e d .  Ramming m i x t u r e s  c a n be e i t h e r w e t  ramming b e i n g made, i n both  o r d r y rammed,  cases, using a metal  the  p l a t e mould  or a s i m i l a r k i n d o f c o r e . The  ideal  g o a l i n p r o d u c i n g a rammed l i n i n g  some 3 0 % o f t h e t h i c k n e s s f u l l y at the working  low p o r o s i t y  f a c e - - t h e r e s t o f t h e l i n i n g s h o u l d be  i n g l y s i n t e r e d and hence date thermal  s i n t e r e d , with  i s to have  more p o r o u s  and m e c h a n i c a l  decreas-  and more a b l e t o accommo-  stresses.  This less sintered  l a y e r a c t s as a c u s h i o n , h o l d i n g t h e h a r d s i n t e r e d " c r u c i b l e " in place.  T o a c h i e v e t h i s , s e v e r a l f a c t o r s m u s t be t a k e n  into  account. The  grain size distribution  s h o u l d be s o a s t o  the d e s i r e d p o r o s i t y i n the u n s i n t e r e d zone dense  structure necessary  distributions  to the w o r k i n g  and a c h i e v e  face.  the  Usually  are very s i m i l a r to the F u l l e r curve  Regarding  produce  (5).  c o m p o s i t i o n , the ramming m i x t u r e w i l l  c o n s i s t o f main c o n s t i t u e n t s and a b i n d i n g a g e n t . of a MgO/MgO.Al^0^.spine1 mixture, to promote s i n t e r i n g  always  In the  f o r i n s t a n c e , SiO^ i s  ( i n a m o u n t s up t o 3% ( 5 ) ) .  these  Care  case added  should  16  be e x e r c i s e d when  s e l e c t i n g the amount and c o m p o s i t i o n  of the  b i n d i n g a g e n t s i n c e i t i s u s u a l l y l e s s s t a b l e a n d , as f a r as attack resistance i s concerned, One s h o u l d u s e t h e m i n i m u m ing  at the d e s i r e d f i r i n g  d e l e t e r i o u s to the  lining.  amount n e c e s s a r y to a c h i e v e temperature.  sinter-  O b v i o u s l y , as t h e  amount o f b i n d i n g agent i s d e c r e a s e d , t h e f i r i n g  temperature  m u s t be i n c r e a s e d u s u a l l y i n t r o d u c i n g t e c h n i c a l  difficulties.  D e p e n d i n g on t h e k i n d o f c o r e u s e d mixture,  firing  c a n be d o n e i n t w o w a y s .  template  was u s e d i n r a m m i n g t h i s w i l l  place during firing that will  quent  I f a mild  steel  u s u a l l y be l e f t i n  m e l t away i n a f i r s t wash  provide the c o r r e c t f i r i n g  case, the lining be f i r e d  and w i l l  f o r ramming t h e  temperature.  In t h i s  s h o u l d be a l l o w e d t o d r y c o m p l e t e l y  under vacuum, t o minimize  wood c o r e i s u s e d ,  firing  in the furnace.  c a n be d o n e e i t h e r b y h e a t i n g up a  c a n be u s e d  to f i r e  g r a p h i t e c o r e be u s e d , vacuum, t o m i n i m i z e core  initial  The use o f t h e wood c o r e i s recommend-  e d s i n c e i t c a n be r e m o v e d a n d a g r a p h i t e c o r e w i t h dimensions  subse-  I f a graphite or a  g r a p h i t e c o r e o r b y r e m o v i n g t h e c o r e a n d m e l t i n g an charge  and then  i r o n o x i d a t i o n and  i r o n o x i d e p i c k - u p by t h e l i n i n g .  heat  up t h e l i n i n g .  the f i r i n g  imprecise  Should a  s h o u l d n o t be made  the r e a c t i o n between the l i n i n g  under and the  (5 ). The  main problem  experienced with monolithic  however, i s c r a c k i n g , s i n c e the l i n i n g mechanical  and thermal  uncommon t o p r o d u c e  stresses.  a lining  with  linings,  i s subjected to severe  During  firing  i t i s not  c r a c k s , p a r t i c u l a r l y as t h e  17  lining  dimensions,  and hence  the s t r e s s e s , are i n c r e a s e d .  When a c r a c k i s f o u n d a f t e r f i r i n g , t h e c r u c i b l e m u s t a l l o w e d t o c o o l , and the c r a c k f i l l e d w i t h cement. thermal  This  c y c l e and the i n t r o d u c t i o n o f a d i f f e r e n t m a t e r i a l  can p r o d u c e  new  cracks.  with large furnaces.  T h i s becomes a very d i f f i c u l t  As S c h l a t t e r a n d S i mko v i ch ( 3 0 )  concerning r e f r a c t o r i e s performance volume s t a b i l i t y , escalated".  (tightness or construction,  this problem  they used r e f r a c t o r y brick/cement excellent crucible lifes.  i n a 6 0 , 0 0 0 l b VIM c o n s t r u c t i o n and  They used Korundal  b o n d e d w i t h M u l l i t e ) as a b a c k i n g  lining,  thermal  or Magnesia  and e i t h e r t h i s  (MagneT) as t h e w o r k i n g  present industrial  problems  r e s i s t a n c e t o c r a c k i n g and s p a l l i n g ) a r e  To a v o i d  stability  problem  pointed  o u t , "as t h e s i z e o f f u r n a c e i s i n c r e a s e d , a l l t h e  spinel  be  lining,  XD  due  furnace,  reported (Alumina  t o i t s good bonded  the l a t t e r  practice in large furnaces.  with  being  Due  to  the the  h i g h d e n s i t y o f t h e XD b r i c k , i t s h o w e d b e t t e r r e s i s t a n c e t o FeO  s l a g s than a 90% Alumina  (28) s t u d i e d the c h e m i c a l  ramming mix  stability  w i t h z i r c o n i a and magnesi te-chrome in contact with d i f f e r e n t carbon observed  t h a t the performance  (29).  Simkpvich  of Korundal commercial  activity  XD as  refractories,  alloys.  t h e s a m e f o r t h e same a l l o y , as f a r a s  consumption  was  As t h e a u t h o r s  b e h a v i o u r o f t h e Z i r c o n i a c r u c i b l e was justify,  He  o f the t h r e e c o m p o s i t i o n s  essentially  concerned.  compared  found,  was  carbon the  indeed d i f f i c u l t to  s i n c e the h i g h e r p o r o s i t y alone would  o v e r r i d e the h i g h e r thermodynamic s t a b i l i t y .  be u n l i k e l y t o The  comparable  18 behaviour present  o f m a g n e s i t e - c h r o m e and no s u r p r i s e , s i n c e  and  10.5%  ^^ °3  and  the  z i r c o n i a c r u c i b l e has  z  the  k i n e t i c basis only  the  the oxides  This  in practice.  carbon contents  these in the  system.  Chester  (52)  to the  in lining  very  but  and  melting  coils.  (larger furnaces)  not experience  penetration  d e p t h o f low  a  possible  In t h e  of  be  In that  the  induced  high the  progressively  case  of  lower  i t is likely that  further heating, frequency  used  use  furnaces.  between the b r i c k s w i l l  metal w i l l  melting,  dangerous s i t u a t i o n  i t is quite  frequency  improved  e a r l i e r by  recommended the  frequency  h e a t e d as i t a p p r o a c h e s t h e  Renkey et a l .  l i f e when b r i c k s w e r e  in induction  metal penetrating  net  r e s u l t s f r o m one  been r e p o r t e d  difficult  melting  expected  d e f i n i t e l y t h e weak l i n k  c a u s e d by j o i n t p e n e t r a t i o n induction  test, detrimental  o r by  observed, in a i r induction  i n s t e a d o f ramming m i x t u r e s ; l a t t e r , due  (30)  the b e s t  the j o i n t s are  substantial increase  to the  g o o d b r i c k l a y i n g and  T h i s e f f e c t has  who  validity  Simkovich  are  encountered.  e f f e c t s are more  are e s s e n t i a l to obtain  linings since  resistance,  Although this point is  "close size tolerances,  mortars"  abrasion  ZrO^)  to give even b e t t e r r e s u l t s .  (29),  in a  M g O / A T ^ O ^ ( M a g n e l ) b r i c k was  e m p h a s i z e d by S c h l a t t e r a n d  of  ( i n c l u d i n g M g O j A ^ O ^ and  fact that gives  The  behaviour  surface)  e s p e c i a l l y s i n c e s u r f a c e / v o 1 ume than  2  u s e d (5u a t the b a t h  f o r the  the  17.4%Cr 02  to f i n d i t s e x p l a n a t i o n  (porosity, strength,  CO  is exactly  The  2  in question  l e s s s t a b l e than  shou1d  former contained  l a t t e r 10%S i 0 .  e t c . ) , s i n c e at the pressure all  a 1umina-si1ica  due  to the  current.  this large  of  19  Bonchack an i n d u s t r i a l  (47) r e p o r t e d s e v e r e e r o s i o n at j o i n t s  VIM  furnace, using Korundal  in  XD b r i c k s a n d  • C o r a l b a n d c e m e n t (82%A1 0 / 1 5 % S i 0 / 2 % T i 0 / 1 % F e 0 ) . 2  3  2  also observed t h a t the j o i n t s with  2  2  He  3  l e s s mortar were  less  e r o d e d a n d c o n c l u d e d t h a t t h e m o r t a r q u a l i t y was  inferior  the b r i c k q u a l i t y .  of a  A1 0^ 2  base  The  need  f o r the development  c e m e n t t o be u s e d b o t h w i t h K o r u n d a l  to  MgO/  XD a n d  Magnel  b r i c k s was t h e n s u g g e s t e d . I t i s i n t e r e s t i n g t o n o t e t h a t the use o f K o r u n d a l in t h e w o r k i n g  l i n i n g i s not i n d u s t r i a l  p r a c t i c e any  more,  s i n c e S c h l a t t e r (53) r e p o r t e d p e r s i s t e n t b o i l i n g w i t h steel  c o m p o s i t i o n s , due t o t h e 8.5%  Si0  2  present in  XD  certain Korundal  XD. The main  d i f f i cu 1 t y w i t h c e m e n t s  f a c t t h a t they s h o u l d bond at r e l a t i v e l y  to the b r i c k  and m o r t a r s  and a c q u i re s t r e n gth  low t e m p e r a t u r e s , s i n c e t h e w h o l e  furnace  be f i r e d f o r t h e s a m e t i m e a n d a t t h e s a m e h i g h as w e r e t h e b r i c k s .  l a r g e r amounts o f f l u x e s than in the b r i c k .  unstable  u n d e r VIM  b o r i d e s ) a n d may out e a r l i e r furnace bonded mm  Unfortunately,  cements  are r a t h e r and  l e a d t o c o n t a m i n a t i o n o f t h e m e l t , as p o i n t e d A 3000kg heat of s t e e l  f o r i n s t a n c e , w i t h 5% a r e a c o v e r e d b y a  o f cement  use  c o n d i t i o n s (as s i l i c a t e s , phosphates  f o r boron.  commercial  cannot  temperature  T h i s makes i t then n e c e s s a r y t o  most o f the f l u x e s used i n commerical  i s the  cement, w i l l  eroded.  in a  VIM  phosphate  a b s o r b a s m u c h as l . l p p m  per  20 1.2.3  Other  Apart  R e a c t i o n s Wi t h t h e L i n i n g  from  r e a c t i o n s i n v o l v i n g oxygen  (oxides) in  the l i n i n g , most o f t h e work done i s r e l a t e d t o d e s u l p h u r i z a tion  (de-S).  Sulphur  removal  by vacuum i s e x t r e m e l y  ineffect-  i ve, e i t h e r as gas 2S = S ( g ) 2  or as v o l a t i l e  compounds as  Sj_ + S = S i S ( g ) T.P. melts--which  Floridis  ( 5 4 ) r e p o r t s 1.25h @ 6u i n C and S i r i c h  i n c r e a s e S a c t i v i t y - - a r e needed t o reduce  content to 50% o f i t s i n i t i a l and  reaction in steel  have been used:  value.  sulphur  S i n c e d e - S i s an  and N i - a l l o y making, three  import-  approaches  the use o f s l a g s , the p a i n t i n g o r c o a t i n g o f  the r e f r a c t o r i e s , and t h e use o f Rare  Earth Metals  (REM).  Ward e t a l . (55) t r i e d s e v e r a l d i f f e r e n t m e t h o d s o f adding  l i m e t o de-S a VIM s t e e l  marble  c h i p s was o f v e r y  formed  a r i n g around  area.  The use o f lime/water  presented  heat.  The use o f c a l c i n e d  l i t t l e e f f e c t since the lime r a p i d l y  the c r u c i b l e wall  reducing the contact  paste over the r e f r a c t o r i e s  the best r e s u l t s , with  very good de-S.  In t h e c a s e  of s p i n e l r e f r a c t o r i e s , however, the lime reacted with the r e f r a c t o r y and s w e l l e d , d e c r e a s i n g t h e i n n e r d i a m e t e r crucible.  A l s o , when u s i n g p u r e  c o a t i n g and adherent  metal  f r e s h a p p l i c a t i o n was m a d e . under  MgO r e f r a c t o r y , t h e CaO  was r e m o v e d a f t e r e a c h This process  present problems  head and a  i s only f e a s i b l e  vacuum due t o t h e h i g h f l u x i n g a b i l i t y  This would probably  of the  F e O h a s on l i m e .  w i t h an i n d u s t r i a l  scrap  21 charge.  A l s o , no o b s e r v a t i o n  i s made w i t h  regard to the'life  of the c r u c i b l e . The  u s e o f s l a g s i n VIM i s e x t r e m e l y  to the f a c t t h a t the whole process Although  very ingenious  proposed  i n p r i n c i p l e (56) i t i s extremely  will  processes  occurs  c u m b e r s o m e , due  in a sealed  f o r slag handling  Besides,  point.  to s o l i d i f y  are heated  Although  there are suggestions  here.  in the center  In o r d e r t o g u a r a n t e e  f l u x i n g a d d i t i o n s such  ies. with  these  as C a F  having  2  a low m e l t i n g  Afanasyev 3  c r u c i b l e s and poured  i s made t o r e f r a c t o r y w e a r a p a r t  crucibles.  Although  values are not given  slags  having melted  either a f t e r or before the  from  over the metal,  severe  i n large  The s l a g s were  i n t h e c r u c i b l e a n d g o o d d e - S was o b s e r v e d .  happened causing  point,  e t a l . (58) t r i e d  C a O / S i 0,,/Al 0 w.i t h 1 ow F e O c o n t e n t s ,  t h e s l a g was p o u r e d  n o t be  v a r i o u s t r i a l s w e r e made  points o f ~1500°C o r 2000°C.  in g r a p h i t e  and w i l l  m u s t be i n t r o d u c e d  difficulties,  2  (57), t h i s  a f l u x i n g e f f e c t on t h e r e f r a c t o r -  siag-desulphurization.  melting  metal  thereby  Despite  in the system  induc-  of using a  i s n o t a common i n d u s t r i a l p r a c t i c e a t p r e s e n t  quantities,  by  i f i t does n o t have a very low  plasma t o r c h t o keep t h e s l a g molten  considered  joints.  and the s l a g i s c o n s t a n t l y r a d i a t i n g t o the f r e e -  i t is likely  melting  they  of the slag  movable vacuum  since only e l e c t r i c conductors  tion heating board,  through  c a n be  unlikely that  s u r v i v e t e c h n i c a l problems as t h e removal  handling tool introduced  chamber.  observations  considerable  No  reference  t h a t when foaming  i n c r u s t a t i o n s in the walls o f the  t h e s l a g s were a n a l y s e d  a f t e r usev t h e  b u t one can a n t i c i p a t e s i l i c a  reduction  22 w i t h CO one  formation  ( e s p e c i a l l y in the h i g h e r carbon  o f the main causes  improved  of foaming.  The  de-S  as  r e s u l t s are  f o r a l l C c o n t e n t s , as c o m p a r e d t o a t m o s p h e r i c  p r e s s u r e de-S,  but the most s i g n i f i c a n t  improvement i s  i n t h e low C ( 0 . 0 3 5 % ) s t e e l , p r o b a b l y  due  FeO  Polyakov  content a c h i e v a b l e under  vacuum.  2  sulphur content  and  concluded  power.  cases.  Volkov  e t a l . (61)  2  3  (59)  slags  on  is only  2  L i n c h e v i s k i i (60)  i n v e s t i g a t e d the use o f both o f CaO/CaF s i u r r i e s p a i n t e d to the w a l l s and  lower  et a l .  t h a t the e f f e c t o f C a F  o f f l u x i n g , h a v i n g no d e - S  found  t o t h e much  i n v e s t i g a t e d the e f f e c t of v a r i o u s C a F / C a O / A T 0  one  melts)  2  mixtures  achieved  and  good de-S  studied various mixtures  of in  CaO both  of  CaO/  C a F , C a O / A l 0 / C a F , C a O / C a F / S i 0 , p l a c e d on t h e b o t t o m  of  the c r u c i b l e .  CaO/  2  10% C a F  2  2  3  2  The  mixture  2  2  b e s t r e s u l t s w e r e a c h i e v e d w i t h a 9.0%  p l a c e d on t h e b o t t o m  of the c r u c i b l e t h a t  would, a f t e r the m e l t i n g p r o c e s s , s i n t e r to the bottom c r u c i b l e , being cleaned a f t e r the pouring. authors  do a d m i t  t h a t t h e u s e o f s l a g s may  of  In t h i s w o r k form  the the  a c c r e t i o n s on  the c r u c i b l e w a l l s , reducing i t s l i f e . S c h l a t t e r e t a l . (62) p a t e n t e d Ca0/CaF  2  o r o t h e r f l u x e s and  having  lower m e l t i n g p o i n t than  T h e i r t r i a l s were p e r f o r m e d Magnel) c r u c i b l e s . erosion critical  Although  the use of m i x t u r e s  a reducing agent, the metal  being  in Magnesia/Spinel  e i t h e r C or  in this  REM,  produced. (possibly  t h e r e i s no r e f e r e n c e t o b r i c k  in the p a t e n t , the c o n t r o l of the s l a g c o m p o s i t i o n (53)  of  respect.  is  23 In a s o m e w h a t d i f f e r e n t a p p r o a c h employed fused deoxidation  l i m e c r u c i b l e s , a ch i e v i n g ex ce 11 en t  by s i l i c o n  (due  i n the r e f r a c t o r y ) and c o o l i n g and crucible in  Strushchenko  to the  lowered  h e a t i n g t o room t e m p e r a t u r e .  ( 2 0 k g ) was  of  SiO^  8 cycles  However the  of  small  f i r e d at 2000°C Which i s not f e a s i b l e  larger scale operations.  hydration • problems,  de-S,  activity  r e s i s t a n c e t o more t h a n  (35)  One  should the  has  a l s o to c o n s i d e r  furnace  the  chamber need to  be  opened f o r r e p a i r s . Several the  literature  r e p o r t s o f de-S (63, 64,  65).  with Small  REM  i n VIM  problems with  able Rare E a r t h Metal  recovery,  melts  of " o x i d e - l i k e " slags  (56), formation  p e r s i s t , but the main problem costumers. -  carry-over to  i s one  exceed  found  unpredict-  (63), etc., by  T h i s i s b e c a u s e t h e e x a c t e f f e c t s o f REM  of d e l e t e r i o u s RE-Fe phase  certain  limits.  except  in  subsequent  of acceptance  to s u p e r a l l o y s are not w e l l u n d e r s t o o d , formation  are  f o r the  ( 6 4 ) when t h e s e  still  the addition known additions  24  1.3  O b j e c t i v e s o f the Research  Project  S i n c e i t i s w e l l e s t a b l i s h e d t h a t i n VIM  furnaces  u s i n g b r i c k - m o r t a r l i n i n g s t h e w e a r i s l o c a l i z e d on t h e mortar  joints  (50,66),  mortar  ( o r c e m e n t s ) by s t e e l s a n d / o r  most i m p o r t a n t  i t was d e c i d e d t h a t t h e a t t a c k o f  p o i n t t o be s t u d i e d .  s u p e r a l l o y s was t h e T h i s s t u d y was t o  e n c o m p a s s b o t h t h e a t t a c k m e c h a n i s m s a n d some r o u g h e s t i m a t i o n of the r e a c t i o n r a t e s , although  no a t t e m p t  e x a c t k i n e t i c s was t o be m a d e .  In a d d i t i o n , a t t e m p t s  be made t o d e v e l o p order t o improve  a cement w i t h o u t  low s t a b i l i t y  the overall lining  performance.  F i n a l l y , samples analysed and  to derive the  o f used  oxides, in  V I M r e f r a c t o r i e s w e r e t o be  and c o r r e l a t i o n s attempted  between these  observations  the test r e s u l t s , in order to verify the v a l i d i t y  experimental  findings.  were t o  of the  25  CHAPTER 2 EXPERIMENTAL In  order to study the attack o f mortar  we p r o p o s e d ,  d i f f e r e n t t e c h n i q u e s were c o n s i d e r e d .  w e t t i n g s t u d i e s ( s u c h as s e s s i l e d r o p s ) to  b y m e t a l s , as  p r e d i c t the s t a b i l i t y  have been  and r e a c t i o n o f metals  Although extended  with  ceramic  substrates  ( S u t t o n ' s ( 1 9 ) , f o r i n s t a n c e ) i t was f e l t  they would  not, in a l lcases, simulate exactly or closely  e n o u g h t h e c o n d i t i o n s o f VIM. cases r e a c t i o n products which d r o p l e t may be f o r m e d  This a r i s e s because  that  i n some  limit the spreading of the  (67) and t h e chemical  composition  of  t h e d r o p l e t may be s u b s t a n t i a l l y a l t e r e d i n a r e a s o n a b l y experiment.  T h i s e f f e c t has been  where t h e r e a c t i o n o f carbon refractories volume r a t i o s  i s concerned  long  noti ced parti cul arly i n cases  i n the metal with the oxide  due t o t h e v e r y h i g h i n t e r f a c e /  (both metal/ceramic  and metal/vacuum).  In  a d d i t i o n i t was d e s i r e d t o a c q u i r e s u f f i c i e n t k n o w l e d g e o f the o r d e r o f magnitude element  losses and/or  estimated in a real  o f t h e r e a c t i o n r a t e s so t h a t oxygen  pick-up  furnace based  alloying  ( i f a n y ) c o u l d be  on t h e d a t a g e n e r a t e d .  a l a s t f a c t o r i t was f e l t t h a t w e t t a b i l i t y t e s t s w o u l d  As over-  emphasize  small variations in surface finish.  Since the  materials  used were e i t h e r commercial  used  products  in real  furnaces or experimental  c o m p o s i t i o n s , they would n e c e s s a r i l y  vary s l i g h t l y i n surface  finish.  26  In crucibles of metal time.  order then  t o s i m u l a t e t h e VIM p r o c e s s ,  as shown i n F i g . 3 were p r o d u c e d , were melted  under  ment o f t h e e x p e r i m e n t a l once,  and no a t t e m p t  quent  heats  of the size  s e t - u p , each  length of  and t h e arrange-  crucible  in a crucible.  was u s e d  only  I t was r e a l i z e d t h a t t h e s u r f a c e /  c r u c i b l e was o b v i o u s l y q u i t e  a s m a l l VIM f u r n a c e ; h o w e v e r , t h i s  experimental  amounts  was made t o s t u d y t h e e f f e c t o f s u b s e -  volume r a t i o i n t h i s to even  and fixed  vacuum, f o r a c e r t a i n  As a n a t u r a l c o n s e q u e n c e  small  case, l a r g e r than  dissimilar  ratio i s , in the  in the actual  case.  Conse-  quently a magnification of the reaction  effects  hence i m p r o v i n g  the a b i l i t y  to assess the s t a b i l i t y  of r e f r a c t o r i e s  i n contact with melts  of the test  e f f e c t p r e s e n t was p o s s i b i 1 i t y by t h e m e t a l , w o u l d  cause  under  i s observed,  vacuum.  Another  that wetting of the crucible  variations  in t h e m e t a l / r e f r a c t o r y i n t e r f a c e s ,  i n t h e vacuum/metal and as shown i n F i g . 4 .  felt,  however, that since these wetting c h a r a c t e r i s t i c s  quite  r e p r o d u c i b l e f o r each  cause  a significant variation  The  of the  in interfacial  refractories  apparatus  under  distance  through  The  a Pyrex  from the metal  order to calibrate pyrometer  area that  glass,  vacuum. The temper-  a narrow-angle  infrared  placed at a s u f f i c i e n t  to minimize  condensation  f o r emi s s i v i t i e s ,  directly controlled  they  of the relative  e m p l o y e d i s shown i n F i g . 5 .  a t u r e m e a s u r e m e n t s w e r e made w i t h pyrometer  were  meta 1/re f rac to ry p a i r and d i d n o t  c o u l d be a s s u m e d n o t t o a l t e r t h e p l a c e m e n t stabilities  I t was  pure  on i t . I n  Fe a n d N i w e r e  t h e power supply  and a  used.  27 v a r i a t i o n w i t h i n + 5°C o f the s p e c i f i e d t e m p e r a t u r e typical. r a t e was  T h e p r e s s u r e was  always  v e r i f i e d before each  was  k e p t b e l o w 30y and t h e l e a k  run.  The c o m p o s i t i o n s o f t h e m a t e r i a l s u s e d f o r t h e  tests  a r e g i v e n i n T a b l e s 5 and 6 and e x c e p t where n o t e d , t h e y a r e nominal  c o m p o s i t i o n s g i v e n by t h e The m e t a l l i c s a m p l e s  with steel  o r 13.5g  A typical ambient  suppliers.  weighed  tests  + O.lg f o r the t e s t s with s u p e r a l l o y s .  melt c y c l e would  temperature  lOg + O.lg f o r the  f o r complete  a s h o r t h o l d i n g time at around s u p e r h e a t i n g to 1520°C  i n v o l v e slow h e a t i n g from  o u t g a s s i n g of the  crucible,  1000°C, m e l t i n g the  ( i n t h e c a s e o f 1095  sample,  s t e e l ) or to  ( i n the case o f N i c k e l v a c X-750) , h o l d i n g a t t h a t  1500°C  temperature  f o r the d e s i r e d p e r i o d o f t i m e , t u r n i n g o f f the power s u p p l y and c o o l i n g to ambient  temperature  under vacuum.  This  was  done i n o r d e r to m i n i m i z e the c h a n c e s o f o x i d a t i o n o f the metallic  sample. The c r u c i b l e s were p r o d u c e d i n a p a p e r m o u l d w i t h a  p a r a f f i n wax temperature  core.  After drying (or s e t t i n g ) at  ambient  they were e i t h e r f i r e d a t the r e q u i r e d t e m p e r a t u r e  (in a g a s - f i r e d f u r n a c e ) or h e a t e d to a t e m p e r a t u r e range of 600°-700°C  in the  to burn t h e p a p e r and t h e p a r a f f i n  wax  and t h o r o u g h l y d r y them. Metal  samples  f o r c h e m i c a l a n a l y s i s were s e p a r a t e d  from the c r u c i b l e s , c a r e f u l l y c l e a n e d of r e f r a c t o r y tions, filed  incrusta-  to e l i m i n a t e open p o r o s i t y and then c u t i n s m a l l  pieces for analysis.  The c a r b o n and o x y g e n  a n a l y s e s w e r e made  28  by t h e c o n v e n t i o n a l t e c h n i q u e s i n L E C O a n a l y s e r s . In o r d e r t o o b s e r v e t h e r e f r a c t o r y - m e t a l i n t e r f a c e s or o t h e r r e f r a c t o r y samples the specimens or removing  without s e p a r a t i n g the metal grains of the ceramic.  t h i s , the samples under  i t was n e c e s s a r y t o c u t a n d  vacuum.  were i m p r e g n a t e d  w i t h 1 ow-vi s cos i t y epoxy, meta11ographic  to l y diamond p a s t e , they were  e i t h e r i n an O p t i c a l  observed  Microscope or in a Scanning Electron  M i c r o s c o p e e q u i p p e d w i t h an X - R a y E n e r g y some  from the ceramic  In o r d e r t o a c c o m p l i s h  A f t e r p o l i s h i n g by s t a n d a r d  t e c h n i q u e s , down  polish  cases the microprobe  was a l s o  used.  Spectrometer.  In  29  CHAPTER 3 RESULTS S i n c e t h e t e s t s made w i t h s t e e l s a n d w i t h s u p e r a l l o y s are a n a l y s e d i n d i f f e r e n t w a y s , as d i s c u s s e d b e l o w , section will  this  be d i v i d e d a c c o r d i n g t o t h e a l l o y u s e d f o r t h e  tests. 3.1  T e s t s Using AISI In  1095 S t e e l  order to avoid problems with variation  and oxygen c o n t e n t and a c t i v i t y ensure  o f carbon  over a wide range,  and t o  r e a c h i n g t h e s t e a d y s t a t e d e s c r i b e d by M a c h l i n , a  high-carbon  s t e e l was s e l e c t e d f o r t h e s e t e s t s .  Although  c a r b o n was t h e e l e m e n t t o be s t u d i e d , t h e i n t e r e s t was i n steel  i n t e r a c t i o n w i t h r e f r a c t o r i e s and so a p l a i n  commercial in  s t e e l was s e l e c t e d .  this steel  2 hours,  consumption  under vacuum.  Tasil  Although  X — ( M u l ' l i t e Based  initial  The t e s t s  content.  Cement)  t h i s p r o d u c t i s n o t d e s i g n e d t o be u s e d i n  contact with metal  i n a VIM f u r n a c e b u t r a t h e r as a  support f o r the coils composition  content  f o r v a r i o u s l e n g t h s o f time, from 5 minutes t o  and t h e m e t a l was a n a l y s e d f o r c a r b o n  3.1.1  oxygen  (due t o the high C content) minimizes  v a r i a t i o n s i n carbon were c o n d u c t e d  The low i n i t i a l  carbon  and t h e l i n i n g i t s e l f ,  makes i t p a r t i c u l a r l y  mechanical  i t smullite  interesting since i t enables  30 one  t oanalyse  silica  the behaviour  activity  refractory mullite silica  to the  in the b i n a r y S i O g / A ^ O ^ j w i d e l y  industry.  composition content  corresponding  Any  minimum used  in  cement w i t h h i g h e r alumina  s h o u l d be designed  in a m u l l i t e form,  the  than  the  s o as to have a l l i t s  to minimize  the  silica  activity. Fig.  6 presents -  (C.  the v a r i a t i o n of carbon  Cp. .• ,) a f t e r m e l t i n g i n T a s i l  initial  very high consumption  is r e a d i l y apparent.  c r u c i b l e s (Alundum  of carbon  The  and  parabolic relationship indicates  of  the m e t a l / r e f r a c t o r y i n t e r f a c e a f t e r a short  (5 m i n s . ) F i g . 7 , o n e  silica  can  s e e how t h e m u l l i t e i s d e p l e t e d  a t t h e i n t e r f a c e and  remaining  i s the d i f f u s i o n o f  oxygen.  Observing time  1139).  b y the m u l l i t e r e f r a c t o r y  that the c o n t r o l l i n g step in the process s i l i con  Xcrucibles,  Tina I  compared with m e l t i n g in alumina The  content  how t h e a l u m i n a  particles  have a h i g h e r s p e c i f i c a r e a , f u r t h e r e n h a n c i n g  dissolution  of the r e f r a c t o r y .  I f one  c a l c u l a t e s the  in e q u i l i b r i u m w i t h pure Rosenqvist  the  (68) 3 A 1  activity  alumina,  of s i l i c a  using the data  from  f o r the r e a c t i o n 2°3  +  2 S i 0  2  =  3 A 1  2°3 *  2 s i 0 2  A G  a v a l u e o f 0.45  in m u l l i t e ,  is obtained.  i n e q u i 1 i b r i urn w i t h p u r e u s i n g the e q u i l i b r i u m  (Mullite) 1600°C  =  6000C  - a~\  C a l c u l a t i n g t h e p r e s s u r e o f CO  silica  or with s i l i c a  at this  activity  31 S  one  + 2_C = 2 CO + SJ_  2  finds P  and hence in  i 0"  mullite  n  cases s i l i c a  of carbon  the a c t i v i t y  under  will  be e x t r e m e l y  by t h e m u l l i t e f o r m a t i o n i s  to the i n c r e a s e i n carbon  d e p r e s s i n g t h e CO  unstable  vacuum, i . e . , the l o w e r i n g i n  of s i 1ica caused  not comparable  3.1.2  a  c 0  in both  presence  -. ^ S i O ? = 0.67 p 2  C 0  activity  caused  pressure.  Cements with  10% S i 0  ( T a y l o r 320,  2  Alundum  F o l l o w i n g the t e s t s with the m u l l i t e based lower  silica  cements were t e s t e d , i n o r d e r to  whether or not they would  1162)  cement,  determine  be m o r e i m m u n e t o a t t a c k by t h e  T h i s c o u l d h a p p e n due t o t h e l o w e r e x p o s e d s t a b i l i t y phase  by  ( m u l l i t e or s i l i c a  area of the  steel.  low-  r i c h compound, s i n c e in  some c a s e s , o t h e r f l u x e s , s u c h a s A l k a l i n e o x i d e s w e r e p r e s e n t ) . In observed.  a l l c a s e s e x t e n s i v e w e t t i n g o f t h e c r u c i b l e was When T a y l o r 320 was  used a f t e r d r y i n g a t  ( s i n c e i t i s r e c o m m e n d e d t h a t i t be u s e d w i t h o u t voilent boil crucible. carbon  firing),  a  out of  the  o c c u r r e d , t h r o w i n g most o f the metal  When t h e s e s a m p l e s  consumption  were a n a l y s e d , t h e y  o f up t o 0 . 1 %  in 5 minutes.  600°C  showed  Since  the  c r u c i b l e s w e r e c e r t a i n l y w e l l d r i e d ( n o t o n l y due  to the  600°C  d r y i n g but a l s o because  vacuum  before  melt-down),  f i r i n g was  of the slow h e a t i n g under attempted  t h a t the most s t a b l e s i l i c a The metal carbon  did not boil  consumptions  w i t h the aim o f making  c o n t a i n i n g phases  would  be  in the f i r e d c r u c i b l e s , a l t h o u g h  were s t i l l  high, being of the order  sure formed. the of  32 0.2%  i n 30 m i n .  refractories  X-Ray d i f f r a c t i o n  on p o w d e r o f  both  r e v e a l e d a low i n t e n s i t y s e t o f q u a r t z p e a k s i n  the u n f i r e d sample, while lower  analyses  the f i r e d sample presented  a much  i n t e n s i t y s e t o f q u a r t z p e a k s as w e l l as p e a k s  sodium-potassium h o w e v e r , was  a1umino-si1icates.  of  The most d r a m a t i c  in the p h y s i c a l appearance  change,  of the c r u c i b l e s , with  t h e f i r i n g b r i n g i n g an e x t e n s i v e d e n s i f i c a t i o n o f t h e s t r u c t u r e , p a r t i c u l a r l y a t t h e s u r f a c e , a s s h o w n i n F i g . 8. probably  T h i s would  be r e s p o n s i b l e f o r t h e h i g h e r s t a b i l i t y  in the  fired  c o n d i t i on . When one crucible  observes  ( F i g . 9) o n e  in s i l i c a  caused  notices a reasonably  by t h e d i f f u s i o n  less s t a b l e component. the high alumina  i n f e r i o r mechanical e a r l y , maybe even  d e n s i t y than to suppose  of  this  Fig. 9 that  had t h e  binding  which  l a y e r has  probably  break  a much  o f f very  d u r i n g the s h r i n k i n g or the c l e a n i n g of  the  furnace.  C e m e n t s P r o d u c e d Us'i n-g F l u o r i d e s  Since the t e s t s with s i l i c a the inadequacy  of s i l i c a carbon  Magnesia  b e a r i n g cements  as a f l u x f o r u s e  s t e e l , i t was  a d d i t i o n s to a l u m i n a spine1-bonded  2  the bulk of the r e f r a c -  that this  s t r e n g t h and w i l l  i n an a c t u a l  contact with  from  region between the g r a i n s  It i s reasonable  3.1.3  decomposition  It i s also obvious  r e s u l t e d i n a much l o w e r  skull,  and  Si0  thick layer depleted  layer depleted in silica'has  phase removed from the  tory.  the a l t e r e d l a y e r o f a 10%  under  revealed  vacuum i n  decided to t r y d i f f e r e n t  in order to promote i t s r e a c t i o n with b r i c k (Magnel) used i n  VIM.  the  33  I t i s known- t h a t f l u o r i d e s a r e v e r y good f l u x e s f o r t h i s system and  (and f o r that matter,  f o r almost  any oxide  system)  t h e y h a v e b e e n u s e d i n many c a s e s t o p r o m o t e r e a c t i o n i n  refractory production (69, 70). effective  Although  i n t h i s t h e y p r e s e n t some l i m i t a t i o n s s u c h a s  e x c e s s i v e a t t a c k on t h e r e f r a c t o r i e s of c l i n k e r ) (69), a decrease alumina  they are very .  (during the production  in sintering  sintering) (70), the possibility  ability of health  (since water soluble f l u o r i d e s are hazardous) flouride emissions  ( i n pure hazards  and p o s s i b l e  d u r i n g f i r i n g . \ However, t h e two  first  l i m i t a t i o n s are a c t u a l l y advantages i n the case o f t h e i r utilization and  i n a cement, i . e . , r e a c t i o n with the r e f r a c t o r i e s  c o n t r o l l e d sintering, in order to achieve a r e l a t i v e l y  porous  product with  little  dimensional  change.  p r o b l e m s may i n d e e d p r e s e n t d i f f i c u l t i e s  T h e two o t h e r  i f not dealt with  care fu 1 l y . The  s e l e c t i o n of a non-water soluble f l u o r i d e , at a  reasonable price, Li  fluorides.  percentage  l i m i t s o u r c h o i c e e s s e n t i a l l y t o C a , Mg a n d  With r e s p e c t to the f l u o r i d e e m i s s i o n s , i f the  of fluoride  i n the cement i s kept at a reasonable  l e v e l , and the amount o f cement m i n i m i z e d , VIM  as p r a c t i c e d i n  o p e r a t i o n s , one s h o u l d n o t e x p e c t a h i g h c o n c e n t r a t i o n o f  fluoride emissions  during the f i r i n g o f the c r u c i b l e .  Due t o i t s r e a d y a v a i l a b i l i t y , c a l c i u m f l u o r i d e selected f o r the i n i t i a l  tests.  was  In o r d e r t o e n s u r e t h e  p o s s i b i l i t y o f f l u x i n g , some c a l c i u m o x i d e was a l s o a d d e d , with the aim o f reaching the t e r n a r y e u t e c t i c at approximately  34 4% C a O / 7 2 % C a F / 2 4 % ' A l g O g .  Of c o u r s e a l l the  2  t e s t e d were s a t u r a t e d w i t h a l u m i n a , the t e s t s b e i n g 82% A l 0 / 1 4 % 2  u s e d was 1139,  the f i n a l  C a F / 4 % CaO  3  A l l the samples  and  were f i r e d  in a g a s - f i red f u r n a c e f o l l o w i n g which composed of ca1ciurn a 1uminates m i c r o s t r u c t u r e shown i n F i g . No spectrum.  f o r m a b i l i t y to  f o r two  hours  they were  o r CA  3  The  1300°C  typical  were p r e s e n t i n the  and,  2  X-Ray  peaks  could  i n some c a s e s C A g .  Only  2 8 % a n d t h e c a l c i u m o x i d e t o 8% c o u l d some be o b s e r v e d .  at mainly  i n c a s e s when t h e a m o u n t o f c a l c i u m f l u o r i d e was  C^A^  the  10.  In a l l c a s e s , t h e c a l c i u m a l u m i n a t e as C A,_  in  alumina  and a l u m i n a , w i t h the  c a l c i u m f l u o r i d e peaks  be i d e n t i f i e d  used  c a s t a b l e cement Alundum  in order to impart p l a s t i c i t y  mixture.  one  where the  2  a c t u a l l y the high alumina  compositions  i n c r e a s e d to  low-melting  p r o d u c t i o n of the c a l c i u m  aluminates  is a t t r i b u t e d to the c o n v e r s i o n of the c a l c i u m f l u o r i d e c a l c i u m o x i d e by one 3CaF CaF  2  of the f o l l o w i n g r e a c t i o n s :  + Al 0  2  2  + H0 2  3  = 2A1F  = 2HF  +  + 3CaO  3  CaO  In o r d e r t o t e s t t h e a d e q u a c y adherence  t e s t s and s t a b i l i t y  d i s p l a y s the r e s u l t s  into  of this material  t e s t s were p e r f o r m e d .  of the adherence  tests.  The  F i g . 11 reaction of  t h e c e m e n t a n d t h e b r i c k i s e v i d e n c e d n o t o n l y by t h e p h y s i c a l o b s e r v a t i o n o f t h e i n t e r f a c e b u t a l s o by t h e c h e m i c a l tion profile. almost  One  should also expect this behaviour  a n y b r i c k , a g a i n due  f1uoride  employed.  to the high f l u x i n g  composiwith  a b i l i t y of the  35 The alumina  same s e r i e s o f s t a b i l i t y  cement A l u n d u m 1139.  t e s t s was  Comparing  performed  F i g s . 12 a n d  13  can see t h a t t h e r e i s no s i g n i f i c a n t d i f f e r e n c e i n consumption  with e i t h e r of the cements,  cement does  not have lower s t a b i l i t y  alumina  with one  carbon  indicating that  than  the  the  original  cement used to produce i t . To f u r t h e r i n v e s t i g a t e t h e p o s s i b i l i t i e s  f 1 u o r i d e - m i n e r a 1 i z e d cements,  of the  i t was  d e c i d e d t o t r y MgF^,  with  the aim o f p r o d u c i n g m a g n e s i a - a l u m i n a  spinel, instead of  calcium-aluminates. F i n e l y ground 1139  MgF^  a n d MgO  were mixed  i n the p r o p o r t i o n s 85% A l 0 / 1 4 % 2  f i r e d at 1300°C, the f l u o r i d e .  i.e., slightly  The  mechanical  MgF /l%  3  MgO  2  Alundum (SP2)  p r o p e r t i e s o b t a i n e d w e r e much and o f t h e c a l c i u m - f l u o r i d e  F i g . 14 s h o w s t h e m i c r o s t r u c t u r e o f  produced.  original  cement) while the i n t e r g r a n u 1 ar m a t e r i a l i s a  alumina  and a l u m i n a .  were  a r e as good  mixture only  consumption  tests  as t h e v a l u e s f o r p u r e  cement, w i t h i n the e x p e r i m e n t a l v a r i a t i o n s . It i s c l e a r then  f a v o u r a b l e f o r use  under  that this VIM  In o r d e r t o i m p r o v e lignin  the  present.  15 s h o w s t h e r e s u l t s o f c a r b o n  in t h i s m a t e r i a l , which  (from  In t h e X - R a y p o w d e r d i f f r a c t i o n ,  and s p i n e l peaks Fig.  alumina  l a r g e g r a i n s are Al^O^  the  material  of spinel  The  and  above the m e l t i n g p o i n t of  s u p e r i o r t o t h o s e o f A l u n d u m 1139 cement (CAF).  with  s u l p h i t e was  added  composition would  be h i g h l y  conditions (at least for steels). its plasticity  and c o l d  as a 1 0 % s o l u t i o n i n w a t e r ,  adherence, mixed  36 with the cement powders. excellent results. was  The  cold adherence  In m o s t t e s t s t h e b r i c k / m o r t a r i n t e r f a c e  s t r o n g e r than the mortar  f i r e d m a t e r i a l was  i t s e l f , and  the s t r u c t u r e of the  n o t a l t e r e d by t h i s a d d i t i o n .  Observing  the f i r e d  i n t e r f a c e , i t was  t h i s cement r e a c t s with the spinel, phase phase  t e s t s gave  noticed that  and w i t h t h e  binding  o f t h e p e r i c l a s e g r a i n s i n t h e Magnel b r i c k , and  t o a l e s s e r e x t e n t w i t h t h e MgO the r e s u l t s  itself  ( F i g . 16).  and c a l c i u m a l u r n i n a t e s , M g F  2  MgO  and s p i n e l w i t h t h e e x c e s s  alumina)  producing highly reactive i t was  decided that,  i n o r d e r t o p r o m o t e m o r e r e a c t i o n w i t h t h e MgO  particles,  A l F ^ s h o u l d be u s e d t o f o r m s p i n e l w i t h t h e MgO T h i s c o u l d be d o n e i n two w a y s :  the Al 0 /MgF /MgO mixture 2  3  2  percentage and A 1 0 2  3  Analysing  a c h i e v e d p r e v i o u s l y (CaF^ p r o d u c i n g h i g h l y r e a c t i v e  CaO  Magnel.  reacts  and  The  By a d d i n g  used, mixed  f o r m e r was  b e t w e e n Magnel: b r i c k s .  lignin  mixture  s u l p h i t e s o l u t i o n and  A g a i n , the c o l d s t r e n g t h and  i t y were v e r y good, i n d i c a t i n g t h a t cements w i t h o u t achieve these p r o p e r t i e s .  The  to the s h o r t r e a c t i o n time  The with alumina  Low  Silica  given to both  Phosphate  Bonded  samples  cements,  was spread  silica  can  however,  probably  due  (2 h r s . ) .  Cement  o t h e r component e x t e n s i v e l y used i n to produce  3  plastic-  binding characteristics  d i d i n o t d i f f e r s u b s t a n t i a l l y from t h o s e o f SP2,  3.1.4  2  s e l e c t e d as b e i n g e a s i e r  3  w i t h t h e 10%  A1 0  based m i x t u r e , w i t h Al  t o do a n d a 7 0 % A l 0 / 1 6 % A l F g / 1 3 % "MgF^/1% MgO 2  from  A l t o  r e d u c i n g the i n i t i a l  o r , by d e s i g n i n g an MgO additions.  grains  connection  is phosphoric acid with  or  37 without s i l i c a .  In o r d e r t o i n v e s t i g a t e t h e b e h a v i o u r o f t h e  p h o s p h a t e b o n d , t e s t s w e r e p e r f o r m e d w i t h T a y l o r 341 It  cement.  i s b e l i e v e d that in a phosphate bonded alumina  m i x t u r e , A1H ^ ( P O ^ ) ^ • 3 ^ 0 ,  the hydrated aluminum-phosphate  phase i s the major phase produced i n the b i n d e r system and, upon  firing,  aluminum  orthophosphate (AlPO^), which in i s o -  s t r u c t u r a l w i t h s i l i c a , w o u l d be p r e s e n t .  The o r t h o p h o s p h a t e  is b e l i e v e d to decompose  reaction  a c c o r d i n g t o the  2 A 1 P 0 .4 = A 1 ,do0 , + P CL. do 0  f o r m i n g A I Z C uo w i t h t n e v o l a t i l i z a t i o n 0  agreement, however,  o f P J2 r .5  T h e r e i s no  c o n c e r n i n g the exact temperature of the  d e c o m p o s i t i o n , K h o r o s h a v i n , e t a l (72) r e p o r t i n g i t s s t a r t at to,  1 4 6 0 - 1 4 8 0 ° C and O'Hara e t a l (71) s t a t i n g t h a t i t i s s t a b l e at l e a s t , 1760°C.  I t i s c l e a r however, that since  i s an o x i d e e v e n l e s s s t a b l e t h a n S i O ^ ( for  P2U,-,"as  compared  process in question partial of  A G  ig73K  =  P °5 2  "55KCa1/mol0  t o - 1 2 5 K C a l / m o l 0^ f o r S i C ^ ) a n d a s t h e  i s t o o c c u r u n d e r vacuum  p r e s s u r e o f ^2^5'  o n e  S n  (and hence  low  ° u l d expect the decomposition  t h e b o n d t o be e n h a n c e d u n d e r v a c u u m  induction melting  of  stee1 . Fig. crucibles.  17 s h o w s t h e c a r b o n c o n s u m p t i o n i n T a y l o r  One c a n s e e t h a t a l t h o u g h t h e y a r e h i g h e r t h a n  those i n the A l u m i n a cement Alundum not of  341  pronounced.  The main  1139, the d i f f e r e n c e i s  reasons f o r the acceptable b e h a v i o r  t h i s c e m e n t a r e t o be f o u n d i n i t s r e l a t i v e l y  c o n t e n t , t h e a b s e n c e o f SiO^  low  and i t s e x c e l l e n t g r a i n  s u r f a c e q u a l i t y and s t r e n g t h as c o m p a r e d  ?2®5  sizing,  to the c o r r e s p o n d i n g  2  38 p r o p e r t i e s o f Alundum 1139. interface  f o r a 15 m i n u t e  Observing the m e t a l / r e f r a c t o r y steel-test in this material (Fig.  1 8 ) , one n o t i c e s no a l t e r a t i o n Although  in the s t r u c t u r e of the  some g r a i n s c a n be s e e n  and a d e p l e t i o n i n p h o s p h o r o u s  cement.  t o be g o i n g i n t o t h e  melt  c a n be n o t i c e d c l o s e t o  the  i n t e r f a c e , t h i s seems to have l i t t l e  o r n o e f f e c t on  the  strength of the m a t e r i a l . 3.1.5  Silica  C o n t a i n i n g Phosphate  Bonded  T h e m o s t w i d e l y u s e d c e m e n t i n VIM Coralbond,  a silica  c o n t a i n i n g phosphate  addition of s i l i c a  and P 0 o  c  f o r m an e u t e c t i c a t 9 0 0 ° C ,  b  c  e u t e c t i c in the high alumina at  1200°C.  Indeed,  p l a s t i c , adherent good  furnaces is  bonded cement.  i s p r o b a b l y made t o i m p r o v e  c o l d s t r e n g t h and to e n h a n c e i t s f l u x i n g  one  cold strength.  any  I t i s hence  The  plasticity,  ability, since  while the lowest  side of the A l f t ^ ^ t ^ ^  observes  to almost  Cement  melting binary is  t h a t t h i s cement i s s u r f a c e , and  silica  extremely  develops  a very  a very d e s i r a b l e cement,  from  t h e s t a n d p o i n t o f i t s a c t u a l u t i l i z a t i o n b y b r i c k l a y e r s on  the  s h o p f l.oor. I t m u s t be k e p t i n m i n d , h o w e v e r , t h a t a l t h o u g h p r o p e r t i e s are important p r o p e r t i e s t o be t a k e n  these  (and a r e , i n s e v e r a l c a s e s , the  i n a c c o u n t when s e l e c t i n g a  mortar)  they are not the only important p r o p e r t i e s of a mortar. t h e c a s e o f VIM  or other processes  i s i m p o r t a n t , one of  in which  should look i n i t i a l l y  In  refractory attack  at the c o m p a t i b i l i t y  the mortar with the c o n d i t i o n s of the process.  case, c o m p a t i b i l i t y with high carbon  only  In  our  a c t i v i t y or very  low  39 oxygen a c t i v i t y metals  under  this  can one  c o n d i t i o n i s met,  application properties final  vacuum i s e s s e n t i a l .  and s t r e n g t h o f a j o i n t b e f o r e f i r i n g . i n t h e c a s e o f VIM  after  proceed to t e s t the ease  I n o t h e r w o r d s , i t may  of  These  a r e n o t as i m p o r t a n t as  q u a l i t y of the m a t e r i a l produced  lining.  Only  and the l i f e  the  of the  pay t o use a cement t h a t w i l l  n o t be a s e a s y t o t r o w e l l o r t o s p r e a d , a n d w i l l  not  produce  as s t r o n g a c o l d j o i n t - - i n o r d e r t o a c h i e v e l o n g e r l i n i n g  life  and b e t t e r m a t e r i a l q u a l i t y . In  a l l steel  tests with Coralbond, although the  w e r e w e l l d r i e d a n d p r e f i r e d a t 900-°G v a r i o u s d e g r e e s b o i l i n g were o b s e r v e d , i n d i c a t i n g interaction. tion  is  f o r carbon  i n C o r a l b o n d as a f u n c t i o n o f t h e s q u a r e  good s t r a i g h t - l i n e  (mullite  consump-  root of time,  cement).  The  P2O5)  i n t h e p o r e s o f t h e r e f r a c t o r y as  It i s i n t e r e s t i n g to note t h a t both  and T a s i l - X p r e s e n t t h e same d e c o m p o s i t i o n  (and  proposed  by M a s s a n d A b r a t i s ( 7 3 ) f o r t h e r e d u c t i o n o f m u l l i t e Fe-C m e l t s .  very  f i t shows t h a t i n b o t h c a s e s the r e a c t i o n  c o n t r o l l e d by d i f f u s i o n , p r o b a b l y o f S i O a n d CO^  maybe o f  of  a strong metal/refractory  F i g . 19 s h o w s t h e r e s u l t s  together with those f o r Tasil-X  samples  by  Coralbond  r a t e i n the. t e s t s  performed. When' (Fig.  Cora 1 bond/meta 1 i s observed  2 0 ) , one n o t i c e s t h e c h a r a c t e r i s t i c s i l i c a  a l s o the t o t a l to  the i n t e r f a c e  decomposition  of tne bond.  note t h a t the bond decomposes  d e p l e t i o n and  It i s interesting  (and the phosphorous  drops) at a c o n s t a n t d i s t a n c e from the working  content  f a c e ( F i g . 21)  40 while the s i l i c a  boundary i s not as linear.  This probably  s u g g e s t s t h a t the phosphate bond decomposes by thermal p r e s s u r e e f f e c t s , w i t h t h e v o l a t i I i z a t i o n o f ^2^5' interface  t n e  n  '9 t  temperature.  It i s a l s o c l e a r again in t h i s case t h a t the p e n e t r a t e s i n t o the p o r o s i t y l e f t by the reduced and  s t r a i  i n d i c a t i n g the isotherm: c o r r e s p o n d i n g t o the  decomposition  (Si02  and  P  2^5^»  anc  *  t n a t  t n e  components  a l t e r e d l a y e r has a much  d e n s i t y than the bulk o f the r e f r a c t o r y .  metal  lower  Evidence of the  cement as source of n o n - m e t a l l i c i n c l u s i o n s  (with or without  entrapped metal) is presented in Fig. 22. I t i s c l e a r from t h e s e o b s e r v a t i o n s t h a t the t i o n o f s i l i c a / p h o s p h a t e bond makes C o r a l b o n d able, as f a r as chemical s t a b i l i t y VIM  combina-  less than  i s concerned,  desir-  f o r use i n  furnaces. 3.1.6  Summary o f S t e e l T e s t s  The  very negative e f f e c t  of s i l i c a with or without  other oxides o ras a 'lower a c t i v i t y been o b s e r v e d . mullite Al  Although  unexpected,  1  form i n a compound the r e s u l t s with  the  cement seemed t o be s u p e r i o r t o t h o s e o f t h e 10%  c e m e n t - - T a y 1 o r 320.  T h i s t y p e o f b e h a v i o u r was  observed in w e t t a b i 1 i t y s t u d i e s performed (74).  has  The  SiO^/  also  by Sveshkov et a l .  reason f o r t h i s behaviour perhaps  can be f o u n d i n  the f a c t t h a t the phases p r e s e n t i n the h i g h e r alumina  cement  are not those p r e d i c t e d by e q u i l i b r i u m c o n s i d e r a t i o n s , s i n c e after firing  i t s b e h a v i o u r was  improved.  I n any e v e n t ,  cements proved u n s u i t a b l e f o r the a p p l i c a t i o n  both  in question  and  41  no f u r t h e r  i n v e s t i g a t i o n was  The  possibility  o f s i l i c a , was  promote bonding The  of using  shown, s i n c e  of the basic alumina  t h e y do n o t r e d u c e  reaction,  the corrosion  constituents  inclusions dissolved  stability do  c h a r a c t e r i s t i c s of the r e f r a c t o r i e s to the e x t e n t of the  although this factor alone  could  are  metal not  prevent  reaction.  In s e v e r a l tory  the  instead  bricks.  indeed important with respect ceramic  f l u o r i d e s as f l u x e s ,  cement e m p l o y e d i n the t e s t s and  to the  physical  undertaken.  cases the c o r r o s i o n was  observed  in the metal  to cause  w h i c h may  o r may  d u r i n g the remaining part  the s t a g e o f f o r m a t i o n and s i z e and  o f one  of the  the formation n o t be  refracof  completely  of the heat depending composition, etc.  on  42 3.2  T e s t s U s i n g X-750 S u p e r a l l o y S i n c e i t soon  became a p p a r e n t  b e t w e e n X-750 ( a n d p r o b a b l y the r e f r a c t o r i e s  under  any  t h a t the i n t e r a c t i o n s  o t h e r low-C s u p e r a l l o y )  vacuum were not enough to cause  easily  d e t e c t a b l e v a r i a t i o n i n any o f t h e a l l o y i n g  i t was  decided instead to concentrate  a l t e r a t i o n s at the meta1/refractory  elements,  interface.  In a d d i t i o n , caused  e i t h e r by t h e d i s s o l u t i o n o f r e f r a c t o r y o x i d e s o r by  Due  to the r e l a t i v e l y  t i t a n i u m and  any  a t t e n t i o n on the a c t u a l  the v a r i a t i o n of the oxygen content of the a l l o y ,  m e n t o f r e f r a c t o r y i n c l u s i o n s was  and  entrap-  to be s t u d i e d .  high percentage  of  chromium in t h i s a l l o y , a l l of which  aluminum have h i g h l y  n e g a t i v e i n t e r a c t i o n c o e f f i c i e n t s w i t h o x y g e n i n Ni a l l o y s (ej  1  = -210, e £  expect  r  = -38.6, e j  a relatively  equi1ibrium  1  = -70 a t  1873°K (75)) o n e  high oxygen content in t h i s a l l o y  with , f o r example, alumina.  This is  should  in  clearly  s h o w n i n F i g . 23, w h e r e t h e o x y g e n c o n t e n t i n e q u i l i b r i u m with alumina percentage  i s shown, f o r a N i - A l a l l o y ,  of aluminum.  lOppm oxygen range superalloys  r e a d i l y see t h a t the  are r a t h e r d i s p l a c e d from e q u i l i b r i u m and to the m e l t i n g p r a c t i c e of  d e o x i d a t i o n with carbon  time  can  usual  of values a c h i e v e d in the p r o d u c t i o n  o n l y b e o b t a i n e d due  elements  One  asa f u n c t i o n of  and t a p p i n g .  can  initial  followed bya d d i t i o n of r e a c t i v e I t i s c l e a r t h a t the  longer the  a f t e r the a d d i t i o n o f the more r e a c t i v e e l e m e n t s  and A l ) t h e c l o s e r the s y s t e m the most s t a b l e mixture  of  of  will  oxides.  approach  holding (as Ti  e q u i l i b r i u m with  43 I t m u s t be s t r e s s e d t h a t i n t h i s quite pronounced equilibria present  deviation  case t h e r e i s a  from the simple d e o x i d a t i o n  o b s e r v e d when s m a l l a m o u n t s o f d e o x i d a n t a r e  (aluminum  deoxidation of steel , for instance).  those c a s e s , the aluminum  In  c o n c e n t r a t i o n i s s m a l l , and i n  the e x p r e s s i o n f o r the a c t i v i t y  c o e f f i c i e n t of oxygen,  fo  n log fo = e°wt%0 +  I e^ w t % i  Al the term c o r r e s p o n d i n g to e ence  between  of oxygen  wt%Al  Q  t h e H e n r i an a c t i v i t y  i s also small.  The  and t h e w e i g h t  differ-  percentage  c a n be n e g l e c t e d , a s s h o w n i n F i g . 23 up t o  a p p r o x i m a t e l y 0.08% t i o n s , one  Al in N i c k e l .  In t h i s r a n g e o f  can use a r e l a t i o n s h i p o f t h e wt%0 wt%Al = Ka 3  composi-  type  2  A ]  0  or 3 l o g wt%0  + 2 log wt%Al  = K'loga.,  n U  2 3 a n d s h o w t h a t l o g wt%,0  i s a l i n e a r f u n c t i o n of l o g wt%Al  As t h e a l u m i n u m however, h  Q  content of the a l l o y i n c r e a s e s ,  the term e'^wt%Al  d e p a r t s from wt%0, h  o  .  ,  c a n n o t be n e g l e c t e d a n y m o r e  a c c o r d i n g to the  = f wt%0 o  and  relationship  . 3 2  While the r e l a t i o n s h i p  h h^^ Q  = K is still  valid  for  a f i x e d a l u m i n a a c t i v i t y , a s s h o w n by t h e e x t e n s i o n o f t h e activity  straight  not l i n e a r l y  line  i n F i g . 23, the w e i g h t p e r c e n t a g e s  r e l a t e d a n y m o r e , due t o t h e i n t e r a c t i o n  are  of the  44  two s o l u t e s i n t h e a l l o y , w h i c h simple Henrian  causes departure from  the  behaviour.  Assuming  t h a t the only s i g n i f i c a n t  i s t h a t c a u s e d b y a l u m i n u m on o x y g e n , o f t h e two e l e m e n t s  interaction  the weight  effect  percentages  c a n be r e l a t e d b y t h e f o l l o w i n g  expres-  s i on h  h  =  o Al  31og  K  a  Al 0 2  h  Q  + 21og  A ]  =  K'  + 3 ( l o g fo + l o g wt%0)  21og w t % A l  + 3e^vit%M  Q  + 31og wt%0  (1) shows t h a t l o g wt%0  function of log wt%Al Al term 3e  h  21og w t % A l  Equation  the  3  wt%Al  K'  = =  i s not a  (1)  K'  linear  , a n d c a n o n l y be a s s u m e d t o be s o w h e n  i s n e g l i g i b l e , which  only happens f o r small  c o n c e n t r a t i o n s of aluminum. I t i s t h e n o b v i o u s why  the r e f r a c t o r y / m e t a l i n t e r f a c e  becomes i m p o r t a n t i n the system, s i n c e i t w i l l thermodynamics  control  the  o f t h e p r o c e s s (by t h e compound f o r m e d ,  and  hence e x p o s e d to t h e m e t a l ) and t h e k i n e t i c s (by  i t s physical  alloy will  characteristics).  of the process,  The oxygen  content o f the  i n d i c a t e the approach o f the system to e q u i l i b r i u m ,  a n d , i f a c o n s t a n t t i m e i s t a k e n as a b a s i s f o r c o m p a r i s o n , the  most s a t i s f a c t o r y  refractory  from t h i s s t a n d p o i n t .  T a b l e 7 shows the oxygen  value found in samples  X - 7 5 0 h e l d f o r 15 m i n u t e s refractory materials.  at 1500°C  in crucibles of  It i s e v i d e n t t h a t the  of  different  refractories  45 composed o f MgO-A^O^ s p i n e l and 8 5 % A l 0 / 1 4 % z  oxygen  MgF /l%  3  and e i t h e r A l ^ O ^ o r M g O  MgO ( S P 2 ) )  2  values amongst t h e samples  (Alumina  present the lowest  f o l l o w e d b y T a y l o r 341  P e r i b o n d  b o n d e d by 4.5% P ° 5 ^ '  (Magnel  2  M  ( 9°  w i t n  S i  0 )> 2  A l u n d u m 1 1 3 9 , t h e c a 1 c i um f 1 t i o r i d e - a 1 umi n a c e m e n t ( C A F ) a n d last,  Coralbond. From t h e s e d a t a i t i s c l e a r t h a t t h e most a d v i s a b l e  r e f r a c t o r y f o r h o l d i n g I n c o n e l X-750 would a high percentage stability  of spinel  oxides, the ideal  T a y l o r 341 p e r f o r m e d h i g h e r than  and as l i t t l e as p o s s i b l e lowcombination  7 ppm i n i t i a l  being  w e l l w i t h an o x y g e n  that of the spinel  hand, Coralbond  Magnel/SP2.  c o n t e n t n o t much  based m a t e r i a l s .  r e a c h e d 6 0 ppm o x y g e n oxygen).  be one c o n t a i n i n g  On t h e o t h e r  i n 15 m i n u t e s  (from  S i n c e i t s main c h e m i c a l d i f f e r e n c e  from T a y l o r 341 i s i n t h e s i l i c a  content and the s l i g h t l y  h i g h e r P 0 g > i t c a n be c o n c l u d e d t h a t t h e p r e s e n c e  of these  2  o x i d e s makes C o r a l b o n d superalloys.  In a real  n e v e r be o b s e r v e d , surface/volume concerned due  t h e l e a s t s u i t a b l e cement f o r m e l t i n g f u r n a c e those h i g h oxygen  r a t i o ; however, as f a r as cement a t t a c k i s  t othe almost  constant  be t h e same o r e v e n low oxygen  pronounced,  p o t e n t i a l i n the metal,  in silica  i n t h i s i n s t a n c e , some e f f e c t on t h e s t a b i l i t y , presented a significantly comparable  more  high d r i vi ng- f o rce f o r the d i s s o l u t i o n . I t  can a l s o be n o t i c e d t h a t t h e v a r i a t i o n  for  will  o f c o u r s e , due t o t h e much more f a v o u r a b l e  the results will  and c o n s e q u e n t  values  silica  lower oxygen  contents.  superalloy melting, the i n i t i a l  activity has, since  value than  Peribond  Coralbond,  It i s unfortunate that in stage o fa heat  involves  46 carbon  d e o x i d a t i o n and hence  activity  o f l a r g e p e r i c l a s e g r a i n s b o n d e d by s m a l l e r g r a i n s , the working  areas exposed Fig.  to the  magnesia  h a v e b o t h MgO  and  in  MgO'Al 0 2  3  metal.  24 s h o w s a c r o s s s e c t i o n o f t h e i n t e r f a c e o f a  from the m e t a l .  The  observed  a n d t h e b r i c k i n F i g . 24 i s due a n d , on t h e r i g h t The  gap  h a n d s i d e , one  i n t e r f a c e when  between  to shrinkage can o b s e r v e  probably spinel. l a y e r would  1)  i n Mg  at  this  and Al , this  from the melt, d e s c r i b e d in a  by t h e f o l l o w i n g p r o c e s s e s :  Dissolution of s i l i c a  from the b i n d i n g phase  t h e p e r i c l a s e g r a i n , due  t o t h e v e r y low o x y g e n  the m e l t and  stability:  low s i l i c a Si0  metal  a periclase  The m e c h a n i s m f o r the f o r m a t i o n o f  be p r e c i p i t a t i o n  Al,Ni alloy  the  during cooling  p i e c e s of oxide a d h e r i n g to the metal  p o i n t i n t h e i n t e r f a c e a r e o f an o x i d e r i c h  2  of  p o t e n t i a l in  = S_i + 2 0  This process will cipitation  X-750  face of a c r u c i b l e d r i l l e d  a f t e r u s e , w h i l e F i g . 25 d e p i c t s t h i s  detached  1%  Magnel  S i n c e t h e M a g n e l b r i c k i s com-  a b r i c k with a diamond d r i l l w i l l  grain.  Peribond.  the meta 1 / r e f r a c t o r y i n t e r f a c e o f the  in this m a t e r i a l .  and s p i n e l  sample  silica  one c a n r a t i o n a l i z e t h e p r o c e s s e s o c c u r r i n g w h e n  is melted posed  to low  c o m p o u n d s s u c h as t h o s e p r o b a b l y p r e s e n t i n Observing  sample  s e v e r e a t t a c k even  c o n t r i b u t e w i t h oxygen  of the most s t a b l e o x i d e s .  f o r the  pre-  47 2) activity  D i s s o l u t i o n o f MgO  coefficient  reactive elements MgO 3)  due  in the melt  t o t h e v e r y low  a f t e r the  Formation  o f s p i n e l o v e r t h e MgO  (3a) 3A i n F i g . 26  o f s p i n e l i n e q u i l i b r i u m w i t h MgO,  reaction of  = Mg0-Al 0 2  s h o w n by l i n e 3B i n F i g . 2 6 . d e s c r i b e d by e q u a t i o n  (3b)  a thermodynamic viewpoint, any  by p r e c i p i t a t i o n  (3b)  3  I t i s c l e a r t h a t the  process  s h o u l d be t h e m o s t f a v o u r a b l e since line  3B w i l l  always  increases.  contents  t o be e x p e c t e d  T h i s i s due  o f t h e p r o c e s s , MgO  may  to the very  low  100  ppm  (3b) o v e r  be a d d e d i n a l a t t e r  step  b e c o m e t h e m o s t s t a b l e o x i d e , due  to  alloys.  (1) and t h e t h e r m o d y n a m i c a d v a n t a g e  ( 3 a ) , f a v o u r r e a c t i o n (3b)  r e s p o n s i b l e f o r the formation One  process.  f a c t t h a t e n o u g h o x y g e n s h o u l d be a v a i l a b l e  l o c a l l y from process  probably  of  magnesium  t h e v e r y s t r o n g i n t e r a c t i o n o f Mg w i t h 0 i n N i c k e l  process  be  at t h i s stage of the m e l t i n g  in amounts over  The  from  o t h e r i n F i g . 26 as t h e o x y g e n c o n t e n t  the melt  Mg  on  A^O^,  2AJ_ + 30 + MgO  Should  grains either  3  a c c o r d i n g t o t h e e q u i l i b r i u m f i x e d by l i n e  before  melt:  melt, 2  reached  the  = Mg_ + 0  Mg_ + 2AJ_ + 40 = M g 0 - A l 0  and  addition of  a s s h o w n i n F i g . 26 f o r 1% A l i n t h e  d i r e c t l y p r e c i p i t a t e d from the  formation  oxygen  as t h e  of  one  of the s p i n e l l a y e r .  m u s t a l s o be a w a r e o f p o s s i b l e k i n e t i c d i f f e r e n c e s  between the p r e c i p i t a t i o n of alumina  or t h a t of s p i n e l , which  48 i n v o l v e more s p e c i e s and o f t h e i n t e r s o l u b i 1 i t i e s various oxides which  may  n o t be n e g l i g i b l e  of  at the  these  tempera-  tures in question. These essentially oxygen  r e a c t i o n s would all-spinel  lining  have the e f f e c t of p r o d u c i n g (or brick) with  e q u i l i b r i u m c o n c e n t r a t i o n which  f o r t h e h o l d i n g o f v e r y low oxygen a l s o a good for  evidence  of the s u i t a b i l i t y  around  3  the alumina  This is  behave almost  When one  produces  as p u r e  to understand  a complete  firing  sheath of  MgO-  s p i n e l , and hence w i t h X-750  A l u n d u m 1139  are e s s e n t i a l l y  and  Coralbond,  for their different  the  behaviour.  observ-  In  and b o t h  Mg  for spinel  precipitation.  One  oxide mixture.  In t h e c a s e i n q u e s t i o n , t h i s p r o v e d  mixture  the  role in  a b s e n t , t h e r e i s no chance  must then  best  alloy.  t h i s c a s e , s i n c e a l l cements are h i g h in a l u m i n a , a n d MgO  cement  achieve the  a t i o n o f t h e i n t e r f a c e a g a i n p l a y s an i m p o r t a n t e l u c i d a t i n g the causes  the  Since the  compares the l a r g e d i f f e r e n c e between  v a l u e s f o r T a y l o r 341,  look f o r the next most s t a b l e t o be  a  of chromium oxides with the oxides of the r e f r a c t o r y  a n d some t r a c e s o f o x i d e s o f o t h e r a l l o y i n g e l e m e n t s  2mm  linings  grains, i t is clear that this  v a l u e s f o r r e s i d u a l oxygen  Ti).  low  favourable  of a l l spinel  s h o w n by t h e c e m e n t S P 2 .  of the MgF^/A^Og mixture  will  be  activity metals.  on t h i s r a t i o n a l e i t i s e a s y  excellent stability  2  relatively  VIM. Based  A1 0  would  an  Alundum 1139, deep, behind  (such  as  f o r i n s t a n c e , p r e s e n t e d a pink l a y e r , about  the i n t e r f a c e , r i c h  in chromium.  This  agrees  w i t h t h e o b s e r v a t i o n s o f S p e n d e l o w ( 4 0 ) when m e l t i n g H a s t e l l o y  49 235  in  alumina  was  greenish,  shown i n  Fig.  crucibles. thin  and v e r y  27.  This  and chromium o x i d e the  case  dense,  of higher  the p a r e n t  crucible.  more open  structure  the  case  precludes  the is  case  a higher  and i m p e r v i o u s  (and  also  P).  minimum p e r c e n t a g e  alumina  (10 ) 5  cussed Al 0 2  3  as  it  the  to the melt 1139,  formation  'sees',  the  contains  The s u p e r a l l o y  alone  mixtures  to a c t as  is  dense  refractory,  essentially,  A1 0^, 2  i n t e r f a c i a l layer  a rather large in  and t h i s  question  contains  element i s (a . c  n  Q  a continuous  t o u n i t y , one s h o u l d source  In  formed of a  a mediocre /h  / h ^ hg = 4.5 (10 ) ( 3) ) . 13  f t l  amount  9  .h si 0 As  the a c t i v i t y c o e f f i c i e n t of SiC^  close  than  however,  of a  i n t o the  in N i c k e l a l l o y s  compared t o a  before, since  Ti)  a real  o1 U£  6.18  in  some P and  as  o f Alundum  though  of s i l i c o n  d e o x i d a n t even when  as  oxygen e q u i l i b r i u m c o n c e n t r a t i o n .  o f C o r a l b o n d , even  dense  silica  seeks  the metal  can d i f f u s e  stages,  of  also  s t a b i l i t y with respect  the m e t a l , a t a l l  and hence  impervious,  r e a c t i o n , a l l o w i n g a lower  to surround  In  341  c o n c e n t r a t i o n than  (and c o n t a i n i n g  l a y e r and t h e chromium o x i d e while  higher  l i m i t s the e x t e n t of the  'crucible'  almost  l a y e r , composed m a i n l y  1139  oxygen p o t e n t i a l phase  its  l a y e r formed i n T a y l o r  i n somewhat  o f Alundum  probably  The  disin  expect t h i s  o f oxygen t o t h e m e t a l .  SiC^/ silica  50  CHAPTER 4 O B S E R V A T I O N S OF I N D U S T R I A L  SAMPLES  In o r d e r t o r e l a t e t h e e x p e r i m e n t a l a c t u a l VIM p r a c t i c e s and t o v e r i f y  r e s u l t s with the  t h e v a l i d i t y o f some o f  t h e o b s e r v a t i o n s made i n t h e t h e o r e t i c a l r e v i e w , from m a t e r i a l s used examined. de-S  i n o r produced  some  by VIM f u r n a c e s  were  These c o n s i s t o f a sample o f s l a g produced  treatment,  samples  of macro-inclusions  s u p e r a l l o y s ; and a Magnel b r i c k used  4.1  failed  i n VIM  in nickel  in a furnace  lining  prematurely.  S a m p l e o f S l a g U s e d i n VIM d e - S  Treatment  In o r d e r t o d e s u l p h u r i z e N i - b a s e  alloys, i t is a  k n o w n p r a c t i c e t o mak.e c a l c i u m o x i d e a d d i t i o n s t o t h e Although  i n most heats  t h e r e i s no problem,  violent slagging occurs analysed  base  melting  s t e e l s a n d n i c k e l - b a s e s u p e r a l l o y s , a n d a rammed VIM which  samples  i n some c a s e s  due t o r e f r a c t o r y a t t a c k .  i s from one o f t h o s e  charge. a  The sample  heats.  F i g s . 28 a n d 29 show t h e c h a r a c t e r i s t i c m i c r o s t r u c t u r e o f t h e s l a g , i n t h e SEM. of calcium aluminates,  The matrix  i s composed e s s e n t i a l l y  w i t h some o t h e r o x i d e s , a s s h o w n b y  t h e MgKa a n d A l K a p h o t o g r a p h s  i n F i g . 29, s e v e r a l small  o x i d e s u l p h i d e i n c l u s i o n s a n d l a r g e MgO  grains.  mixed-  51 The significant adequacy  f i r s t o b s e r v a t i o n t o be made i s r e l a t e d t o s u l p h u r c o n t e n t o f the s l a g , c o n f i r m i n g  of this treatment  the l a r g e magnesia  as a de-S  treatment.  However,  tory used, which  was  It i s c l e a r then  t h a t , a p a r t from d e s u l p h u r i z i n g the  magnesia  a d d i t i o n a l s o f l u x e s the b i n d i n g phase the c a l c i u m aluminates The  which  rammed  o f the l i n i n g  c a l c i u m o x i d e has been  the low m e l t i n g m i x t u r e s These,  combined  lime producing  o f MgO,  spinel  treatments,  absorbed and  to  calcium  produce aluminates.  w i t h the a b s o r p t i o n o f o x i d e s o f elements  as Z r and T i f r o m in t h i s  lining.  c a n be p o s s i b l y  a t t r i b u t e d to the c u m u l a t i v e e f f e c t o f v a r i o u s sufficient  refrac-  c o n s t i t u t e the bulk of the s l a g .  f a c t t h a t t h e f l u x i n g o c c u r s i n some h e a t s  until  the  g r a i n s c l e a r l y o r i g i n a t e from the a spine1-bonded  the  the s k u l l , have a very h i g h f l u x i n g  ability  system. It i s i n t e r e s t i n g to compare these o b s e r v a t i o n s  t h e c o m m e n t s by W a r d e t a l . ( 5 5 ) , w h e n e m p l o y i n g desu1phurization Magnesia  linings.  treatment  in e i t n e r Magnesia  He o b s e r v e d  a f t e r the t r e a t m e n t s Magnesia  such  definite  with  a lime  S p i n e l or  s w e l l i n g i n the  pure former  w h i l e no a l t e r a t i o n o c c u r r e d i n t h e  l i n i n g s , p r o b a b l y due  to the absence  of  alumina.  52 4 .2  Magnel  Brick  A sample of Magnel b r i c k from a l a r g e VIM  furnace  was  the working  lining  e x a m i n e d , both m a c r o - and  of  microscopic-  al l y . 4.2.1  Macroscopic  Metal was  f i n i n g was  the reason  still  Observation  why  the  found  i n the C o r a l b o n d  l i n i n g was  removed.  effort. i n VIM  This confirms  the o b s e r v a t i o n s  t h a t the w o r s t  b r i c k l i n i n g s i s at the working  of metal  also observed  ( F i g . 30)  face  is  i n t o the Magnel b r i c k i t s e l f .  o f the r e g i o n c l o s e to the w o r k i n g 4.2.2  Microscopic  aluminates).  In o r d e r t o s t u d y observations  of calcium  metal  i n the r e f r a c t o r y ,  one  the mortar  can  and  aluminates  was  found  also expect  t o be  In a d d i t i o n , a s F i g s . 3 2  and  low  the  by w h a t a p p e a r s  bricks  The  pre-  rather intriguing, CaO  content  33 s h o w , t h e m e t a l  seems  i n t o the r e f r a c t o r y p a r t i c u l a r l y v i a these  This occurs  calcium  j o i n t s are  i n c l u s i o n content of the melt.  s i n c e Magnel i s s u p p o s e d to have a very  f i n d i t s way  w e r e made  i n c l u s i o n s ( s p i n e l , alumina  the weakest l i n k i n the system,  the  Observation  T h i s shows t h a t a l t h o u g h  to c o n t r i b u t e t o the  penetration  face.  F i g . 31 s h o w s some e n t r a p p e d which a c t u a l l y contains  problem  joints.  a considerable  mechanism of t h i s process, m i c r o s c o p i c  ates.  there  a c o n s i d e r a b l e w a s t e o f m a t e r i a l and b r i c k l a y i n g  One  6).  Since  which  quite a substantial thickness of brick a v a i l a b l e , this  represents  sence  joints,  t o be m e l t i n g  and  (Table to alumin-  dissolu-  53 tion  ( F i g . 3 2 ) , o r p o s s i b l y by f l u x i n g w i t h  Ti0  or Zr0  2  2  (Fig. 33). The  calcium  aluminates  phase i n the p e r i c l a s e grains the  brick.  occur  a s an  intergranular  close to the working  When o n e o b s e r v e s t h e p e r i c l a s e g r a i n s  face o f i n unused  Magnel b r i c k , F i g . 34, one sees t h e t y p i c a l s t r u c t u r e p u r i t y p e r i c l a s e , i n w h i c h t h e MgO g r a i n s b o n d e d a n d b o n d e d by a c a l c i u m T h e r e has been c o n s i d e r a b l e tion o f this s i l i c a t e ratio  intergranular  phase.  phase, both with  respect  content  (77).  composi-  to the CaO/Si0 The C a 0 / S i 0  2  2  c o n t r o l , i n the system CaO/Si0 /Mg0, t h e amount and 2  temperature a t which  t h a t r a t i o_s g r e a t e r no  direct  w o r k d o n e on t h e d e s i r a b l e  (76) and to the impurity  ratio will the  silicate  are both  o f high  than  liquid will  be f o r m e d .  about 2 o r very  l i q u i d i s t o be p r e s e n t  at 1600°C.  I t i s known  low s h o u l d  be u s e d , i f  In t h e case  o f Magnel,  i t seems t h a t t h i s r a t i o i s a r o u n d ^ which i s recommended f o r E l e c t r i c furnace  and Open-Hearth a p p l i c a t i o n s  tent of impurities dihedral  angle  amongst those  (other  oxides)  h a s a m a r k e d e f f e c t on t h e  o f the l i q u i d phase, Alumina and T i 0 causing  pronounced lowering  promoting l i q u i d penetration refractory  ( 7 7 ) . The con-  being  2  i n this angle,  hence  into the grain boundaries and  disruption.  When M a g n e l i s u s e d f o r s t e e l o r s u p e r a l l o y under vacuum, two main p r o c e s s e s tion of s i l i c a  and formation  T h e s e two p r o c e s s e s intergranular  occur.  Reduction  melting or dissolu-  of alumina a t the working  c a n l e a d t o an i n c r e a s e  l i q u i d phase o r t o the lowering  face.  i n the amount o f o f the liquid  54 formation  temperature.  g r a i n , 15 mm a w a y f r o m  Indeed,  F i g . 35, shows a p e r i c l a s e  the metal/refractory i n t e r f a c e where,  b e s i d e s t h e l a r g e r amount o f i n t e r g r a n u 1 a r compound, one n o t i c e s a change i n i t scomposition and  an i n c r e a s e i n a l u m i n a  content.  with  a decrease  As o n e g e t s  the i n t e r f a c e , t h e r e i s v i r t u a l l y no s i l i c a granular liquids probably  are b a s i c a l l y o f the system  with small  left  in silica  closer to and the i n t e r -  CaO/A1^O^/MgO ,  fluxing additions of other oxides, f o r  instance TiO^. One  can a l s o observe,  the presence  i n some i n s t a n c e s  of a layer of calcium aluminates  the m e t a l ,  probably  of  course,  be a p o s s i b l e s o u r c e  in  the melt. Although  (at  drained intergranu1 ar liquid. This of calcium aluminate  importance chemical 2  than  small  shows t h a t  even  they would  have  I t a l s o draws a t t e n t i o n t o t h e  o f the t o t a 1 a n a l y s i s o f the r e f r a c t o r y , both a n d p h y s i c a l , s i n c e t h e c o n c e n t r a t i o n o f CaO a n d  i n an i n t e r g r a n u l a r p h a s e makes t h e b r i c k l e s s r e s i s t a n t i t c o u l d b e i f , s a y , f u s e d MgO g r a i n s , o f t h e s a m e  composition  were  Fig. at  will,  ther e f r a c t o r i e s  contribute i n c l u s i o n s , although  a much l o n g e r u s e f u l l i f e .  with  inclusions  t h e a t t a c k on t h e b r i c k i s o b v i o u s l y  i f a more s u p e r i o r cement were d e v e l o p e d ,  Si0  in contact  l e a s t c o m p a r e d t o t h a t on t h e j o i n t s ) t h i s  would s t i l l  (Fig. 36),  the working  bulk  used.  37 s h o w s a l a y e r o f s p i n e l o v e r a p e r i c l a s e g r a i n face, supporting the experimental  observations  p r e s e n t e d e a r l i e r a n d t h e t h e o r y t h a t s p i n e l s h o u l d be t h e  55  most s t a b l e oxide phase i n c o n t a c t with N i c k e l - b a s e d  super-  a l l o y c o n t a i n i n g high percentages o f aluminum i n a Magnel cruci ble.  56 4.3  Inc1usions  in Ni-Based  Although produces  Superalloy  i t i s w e l l known t h a t v a c u u m i n d u c t i o n m e l t i n g  c l e a n e r m a t e r i a l than a i r m e l t i n g  a r l y i n the case this is mainly the system, nitrides.  (5, 51),  particul-  of superalloys containing r e a c t i v e  elements,  due  to the e l i m i n a t i o n o f the atmosphere  p r e v e n t i n g the e x c e s s i v e One  by m e c h a n i s m s s u c h  r e f r a c t o r i e s can  as e r o s i o n , a n d  discussed in the previous  that stable nitrides  chemical  I t i s now  I t becomes then  tion  attack  as  in the  promote the formation alloy with  to recognize that there w i l l  products  o r VAR  of paramount importance  as f e r r o - c h r o m i u m  are  and  alloy.  to control  of those  inclu-  high nitrogen  content,  B e s i d e s , one  must  be s o m e i n c l u s i o n f o r m a -  from the r e f r a c t o r i e s , s i n c e a l l o b s e r v a t i o n s  no p r e s e n t VIM  produced  as T i ( C N ) )  i n VIM  f e r r o a l l o y s with high oxide content, etc. be r e a d y  be  well established  h e n c e , once f o r m e d , wi11 most 1 i k e l y remain  the f a c t o r s t h a t w i l l  still  and c a r b o n i t r i d e s ( s u c h  h a r d l y a f f e c t e d by t h e u s u a l t r e a t m e n t  and  that  c h a p t e r , and t h a t t h e s e  i n m o s t c a s e s , be o x i d e s .  s i o n s , such  of oxides  m u s t be a w a r e , h o w e v e r , o f t h e f a c t  'exogenous' i n c l u s i o n s from  will,  formation  from  r e f r a c t o r y c a n be c o n s i d e r e d t o t a l l y  show t h a t inert  under the p r o c e s s i n g c o n d i t i o n . In o r d e r t o i l l u s t r a t e of Ni-based  these  s u p e r a l l o y f r o m a VIM  c o m m e n t s , some  f u r n a c e were  samples  examined.  F i g . 38 s h o w s ca 1 c i um a 1 umi n a t e i n c l u s i o n s t r i n g e r s in a p a r t i a l l y these  f o r g e d VIM-VAR s u p e r a l l o y .  i n c l u s i o n s i n more d e t a i l  When o n e  t h e y show s m a l l  examines  entrapped  57  m e t a l p a r t i c l e s a n d a r e s u r r o u n d e d by s m a l l e r nitrides  ( F i g . 39).  This would i n d i c a t e that they  p a r t i a l l y m o l t e n a t some s t a g e they  tend  to c l u s t e r during  due t o f a v o u r a b l e  titanium  surface  of the processing  melting  were and  and r e m e l t i n g ,  that probably  energy considerations.  I n F i g . 40  one s e e s a s p i n e l i n c l u s i o n , f o u n d i n a n o t h e r s a m p l e the  same m a t e r i a l .  core  or these should  composition addition  (since there  i n t h i s case  form o f a small ments).  products  i n c l u s i o n s , i t seems r a t h e r  i f not f o r t h e i r size nucleated  i n the m e l t ) ,  i s no i n t e n t i o n a l c a l c i u m  addition  i n t e r a c t i o n s observed  previously  These i n c l u s i o n s would only  and l a t e r i n t o the  were since  the formawithout  into the  ingot.  One i s l e f t t h e n  r e m o v i n g them, by a d e q u a t e p o u r i n g and h o l d i n g  improve-  have t o c l u s t e r i n  and p r a c t i c e , t h e f o r m a t i o n  c a n n o t e a s i l y be a v o i d e d .  a slag.  o r CaO  inclusions  It i s a l s o c l e a r that i n the present  dish design  for their  the b r i c k s ,  the m e l t w h e t h e r f l o a t i n g o r n o t a n d f i n d t h e i r way  tory technology  (too large  inclusions  could explain  tion of large s p i n e l or calciurn aluminate  tundish  materials  o f Ni-Mg a l l o y f o r w o r k a b i l i t y  I t i s e a s i e r to believe that those  difficulty.  clear  and the only magnesium added i s i n the  formed from i n t e r a c t i o n s o f the metal with the  discuss  be r e l a t e d t o r e f r a c t o r y  e m p l o y e d i n t h e VIM f u r n a c e , t o be d e o x i d a t i o n  from  Although i t i s not our purpose to  in depth the genesis that t h e i r oxide  carbo-  time,  state of refraco f these with  temperature  inclusions  the option control,  and perhaps a l s o p o u r i n g  of  tunthrough  58  4.4  P i e c e o f Rammed L i n i n g As d i s c u s s e d b e f o r e , i n d u s t r i a l l y , t h e a l t e r n a t i v e t o  brick/cement  lining  i s a rammed l i n i n g .  c a r e f u l l y sized mixture roughly  in a 60%MgO/40%A1 0 2  superalloy Nimonic 4.4.1  failed  t i o n on t h e w o r k i n g  3  case,  p e r i c l a s e and  composition  was  a  silica,  used to melt  the  901.  Macroscopic  The  these  of alumina,  In t h i s  Observation  l i n i n g shows metal f a c e arid m e t a l  c r a c k s b e i n g the  reason  why  i n c r u s t a t i o n and  fins the  along cracks  l i n i n g was  penetra(Fig.  removed  41)  from  service. 4.4.2  Microscopic  Observation  F i g . 42 s h o w s t h e s t r u c t u r e o f t h e away f r o m t h e m e t a 1 / r e f r a c t o r y  interface.  rammed l i n i n g  I t shows a s i n t e r e d  m a t r i x e s s e n t i a l l y composed of s p i n e l , s u r r o u n d i n g periclase  grains.  t h e l a r g e MgO presented  The  very  much  forwarded  for  most i n t e r e s t i n g c h a r a c t e r i s t i c o f the  mat-  i s t h a t t h e s i n t e r i n g i s q u i t e i n h o m o g e n e o u s , i . e . , some  regions are densely probably CaO  large  in the s l a g sample p r e v i o u s l y  (4.1), in agreement with the theory  their origin. rix  These p e r i c l a s e g r a i n s , resemble  g r a i n s found  6cm  bonded, while others are porous  l o o s e l y bonded.  ratio The  One  also observes  i n d i c a t i n g the p o s s i b l e presence  and  a very high of  oxides.  2  forsterite.  m e t a l / r e f r a c t o r y i n t e r f a c e s h o w n i n F i g . 43  sents a l a y e r of T i / A l  Si0 /  T h i s l a y e r , as i n t h e  pre-  case  Magnel b r i c k s , c o n t r i b u t e s macro i n c l u s i o n s to the melt  of  when  59 eroded  ( F i g . 4 4 ) . C1 o s e t o t h i s 1 a y e r , t h e r e i s c o m p l e t e  dep1etion  o f s i l i c a i n the r e f r a c t o r y , the i n t e r g r a n u l a r volumes b e i n g filled  by m e t a l  layerandby  i n a region very c l o s e to the T i / A l  oxide  T i / C e o x i d e mi x t u r e s f u r t h e r i n t o t h e 1 i n i n g ( F i g . 4 5 ) .  T h i s c a n be r a t i o n a l i z e d i n t h e f o l l o w i n g m a n n e r . Silica  d i s s o l v e s i n t h e low o x y g e n a c t i v i t y  the oxygen content tion.  locally  i n t o the range  In t h e c a s e o f N i m o n i c  (as c o m p a r e d to X-750) and  901,  both  alloy,  of oxide p r e c i p i t a -  the high T i  t h e h i g h Fe c o n t e n t  oxides  cases.  to the m e l t ,  t h e Mg  and  decreases  of  Ti/Al  as o b s e r v e d  Since there is very l i t t l e  MgO  exposed  Titanium oxides  are e x c e l l e n t fluxes in  s h o u l d d i f f u s e r e a d i l y i n t o the l i q u i d  matrix,  d e c r e a s i n g the d i h e d r a l a n g l e , i n c r e a s i n g the amount of p h a s e and  hence enhancing  grains of r e f r a c t o r y . p o s s i b l e that a heat  The  metal  l i t t l e evidence  liquid  by s e p a r a t i n g  the  i t i s not known, i t i s q u i t e  from t h i s l i n i n g would c o n t a i n a s l a g caused  by CaO  a d d i t i o n as  s u b s t i t u t e d by t i t a n i u m  discussed  oxide.  f i n / r e f r a c t o r y c r a c k i n t e r f a c e shows of reaction.  s h o u l d h a v e o c c u r r e d due geneous expansion  the a t t a c k p r o c e s s  Although  v e r y s i m i l a r t o t h e one b e f o r e , w i t h t h e CaO  in  a v a i l a b l e for s p i n e l p r e c i p i t a t i o n would  be r e a d i l y e x h a u s t e d . t h i s system  and  the p r e c i p i t a t i o n of a mixture  i n s t e a d o f C r / A l o r Mg/Al o x i d e m i x t u r e s  the p r e v i o u s  content  (which  i n c r e a s e s t h e e f f e c t i v e n e s s o f T i as a d e o x i d a n t t h a t of Cr) f a v o u r s  bringing  This i n d i c a t e s t h a t the  to thermal  s t r e s s e s caused  o f t h e l i n i n g , and  wets the r e f r a c t o r y and  penetrates  t h a t the metal  i n t o the  crack.  very crack  by  inhomo-  simply  60 One a l s o n o t i c e s n o a l t e r a t i o n i n t h e f u s e d MgO ( F i g . 46) w h i c h a r e e v i d e n t l y more s t a b l e than  grains  the s i n t e r e d  p e r i c l a s e grains of Magnel. The ment w i t h  presence  of cerium  i s probably  REM, a s d e s c r i b e d b y C r e m i s i o  is a very e f f e c t i v e technique  due t o a de-S t r e a t -  (63) and o t h e r s .  and i t s use has been  This  discussed  p r e v i o u s l y , the only p r a c t i c a l l i m i t a t i o n to i t s a p p l i c a t i o n being  t h e REM r e s i d u a l s a n d c a r r y - o v e r Rothman  into the f i r s t performed. Cremisio  problems.  ( 6 5 ) r e p o r t e d a s i g n i f i c a n t c a r r y - o v e r o f Ce heat  Although  i n a c r u c i b l e a f t e r t h e REM t r e a t m e n t  he a t t r i b u t e d t h i s o n l y t o t h e s k u l l ,  (63) suggested  t h a t the r e f r a c t o r i e s c o u l d play a  r o l e i n t h e r e v e r s i o n o f Ce i n t o t h e s u b s e q u e n t its recovery  was  uncertain.  I t i s also noteworthy  heats, that  making  Cremisio  w h e n Ce d e s u l p h u r i z i n g N i m o n i c 9 0 1 r e p o r t e d t h e " d e v e l o p m e n t o f an i n n o c u o u s  ' o x i d e - l i k e ' c o v e r on h e a t s  containing  which would c e r t a i n l y confirm our observations  on t h e  o f Ce i n t h e l i q u i d p h a s e o f t h e r e f r a c t o r y , e n h a n c i n g mechanical  break-up.  cerium" presence its  61  CHAPTER 5 CONCLUSIONS AND 5a. simulate  The  the  materials  tests  initial  (less  deoxidized.  In  be e s s e n t i a l l y  with  the  obvious  of  superalloys  the h e a t ,  in which  r e a c t i v e elements)  this  will  performed with  part  the  RECOMMENDATIONS  stage, the  however,  same as  differences  are  the a t t a c k  that  of the  t h a t the  in a s u p e r a l l o y  is  in  AISI  steel,  the p r o c e s s i n g  substantially  lower  Hence, observed melting  the  fact that melting  t o be more  aggressive  of N i c k e l - b a s e d operating  a t the  steel/refractory 5b.  presence  The e x t r e m e l y  in metals  low o x y g e n - l o w  silicon  as  in  a component  Unfortunately,  for  used f o r refractory  totally silica  refractory its  refractory  frustrates  f o r VIM as  make  it  of a r e f r a c t o r y .  used present  is  of  are  steels.  usually than to  the  attack  products  time. of  silica  or it  in  in  the  contact  a very  poor  with choice  applications.  excellent  difficult  most a t t e m p t s  that  an i m p u r i t y  fabrication, its  production design  makes  presence  carbon  related  absence  vacuum  superalloys  besides  f r o m the also  any  under  tests,  refractories  low s t a b i l i t y  carbon  mechanism  f o r most  steel  a t any  raw  temperatures  can be  and the  interface  than  than  of  to the  superalloys  temperature  of carbon  lower  for Ni-supera11oys  higher  ores  that  much  of  not  and  steel  amount  deoxidant  and  the  molten  as  1095  do  i n many properties  to e x c l u d e  The  it  low s t a b i l i t y  t o combine  it  in  of  a lower  62  a c t i v i t y f o r m - - s u c h as m u l 1 i t e - - t o elements. selects with be  From t h e s e  conclusions  a cement ( o r any  to i t s s i l i c a  furnace,  content,  by  reacti  i t i s c l e a r t h a t when  refractory that will  t h e m e t a l ) f o r a VIM  given  reduce i t s attack  be  in  contact  special attention  i f the  best  one  should  r e s u l t s are  to  be  achieved. A l t h o u g h the silica  containing  to the  reaction  observation  c o n t r o l l i n g step  c e m e n t s s e e m s t o be  of the  hope t h a t s t e e l  altered portion in t h i s context)  ' w a s h - h e a t s ' may  that there  of the b i n d i n g  the  properly  as a l i n i n g  silica  is hardly  to the m e t a l , during  the  the  layer.  The  fragile  and  that would  charging  any  any  l i n i n g by  phase r e s u l t s in a very adhering  physical  a c t u a l l y accomplish  o f a s i 1 i c a - d e p l e t e d , more s t a b l e  porous l a y e r , strongly function  (difusion)  of the medium-high  w a s h i n g , in the sense of c o n d i t i o n i n g  removal  its transport  of  i n t e r f a c e , i t i s a l s o c l e a r , from the  c e m e n t s ( 5 - 1 0 % S i 0^  production  in the c o r r o s i o n  not  o f the  next  heat. One  mi g h t  t o be u s e d , t h e y preferably with  the  should  be o f v e r y  of a Nickel-base  The  cement grains  and  i n any  stability.  use  Best  that i f firing low  heats  t h i s be  compatible  firing.  o f f l u o r i d e s to promote the  t h e i r reaction with  the  bonding  refractory  of the t e s t s , compromise the b a s i c r e s u l t s are  of elements which form oxides o f the m o r t a r o r the b r i c k .  are  r e a c t i v i t y , and  a l l o y , should  temperatures needed for 5c.  did not,  r e commen d t h e n ,  obtained  by s e l e c t i n g  that react with In some c a s e s  the  of  bricks grain  fluorides basic  as s h o w n i n  oxide the  63 tests of CaF2/Al20  3  of the b a s i c alumina and  improved  alloy.  and  M g F g / A ^ O ^ c e m e n t s , t h e same  was  observed  s t a b i l i t y was  The  stability  when i n c o n t a c t w i t h  steel  shown when i n c o n t a c t w i t h a  f a c t t h a t the f l u o r i d e - c o n t a i n i n g mixtures  w i t h Magnel b r i c k s enhances t h e i r cementing  superreact  properties.  It is  f e l t t h a t t h e u s e o f t h e A l 2 0 / M g F 2 / M g O c o m p o s i t i on  developed  i n t h i s work w i t h a more r e a c t i v e and b e t t e r s i z e d  alumina  3  powder and c o n t r o l l e d a d d i t i o n s o f l i g n i n  s u l p h i t e to  the b r i c k l a y i n g needs would present a d e f i n i t e the chemical analogous  s t a b i l i t y o f t h e VIM  composition,  present very promising  results.  i m p r o v e m e n t can p r o b a b l y ( A l F ^ o r MgF2) f o r s i l i c a MgO/40%Al20  3  5d.  improvement in  furnace linings.  u s i n g a b a s i c MgO  satisfy  g r a i n and  Also,  an  A l s h o u l d  As a c o r o l l a r y , c o n s i d e r a b l e  be a c h i e v e d by s u b s t i t u t i n g f l u o r i d e s i n ramming m i x t u r e s  such  as t h e  60%  previously described. The  p h y s i c a l c h a r a c t e r i s t i c s o f t h e r e f r a c t o r y can  h a v e a d e f i n i t e i n f l u e n c e on t h e k i n e t i c s o f a t t a c k , as s h o w n by t h e t e s t s w i t h f i r e d a n d u n f i r e d T a y l o r 320 c e m e n t . in a l l cases, f i r i n g to a temperature  This suggests that  as h i g h a s p o s s i b l e s h o u l d be  a t t e m p t e d , b e f o r e b r i n g i n g a new l i n i n g o r t u n d i s h i n s e r v i c e . T h i s w i l l a l s o h a v e f a v o u r a b l e e f f e c t s on t h o r o u g h l y d r y i n g t h e refractories.  One  should not expect,  however, dramatic  ments i n the c a s e o f m a t e r i a l s o f r e c o g n i z e d low 5e.  Since the presence  of comparatively  ages of aluminum (or other elements  with  stability. high  high a f f i n i t y  oxygen) s u b s t a n t i a l l y lowers  the a c t i v i t y c o e f f i c i e n t  oxygen in a s u p e r a l l o y melt,  the oxygen c o n t e n t  will  be g o v e r n e d  by t h e f o l l o w i n g f a c t o r s :  improve-  percentfor of  in these a l l o y s  64 1.  Phases (and compounds) p r e s e n t a t the metal/ refractory interface  2.  Time o f h o l d i n g i n the c r u c i b l e  3.  Physical c h a r a c t e r i s t i c s of the i n t e r f a c e .  The  first  factor will  c o n t r o l the e q u i l i b r i u m oxygen  c o n t e n t o f t h e a l l o y , by f i x i n g t h e o x i d e a c t i v i t i e s , the o t h e r two w i l l dissolution  determine  while  the kinetics o f the oxide  process.  It follows then, that the best s e l e c t i o n o f a r e f r a c t o r y f o r VIM ( f o r b o t h mixture  s t e e l s and s u p e r a l l o y s ) w i l l  be a  o f o x i d e s w i t h as h i g h as p o s s i b l e a s t a b i l i t y  r e s p e c t t o c a r b o n , high m e l t i n g p o i n t and good properties.  mechanical  A l s o , aluminum i s u s u a l l y present i n high  q u a n t i t i e s i n s u p e r a l l o y s t o be t h e e l e m e n t t h a t w i l l the oxygen p o t e n t i a l . low a l u m i n a  with  activity  enough control  I t i s t h e r e f o r e d e s i r a b l e t o have as as p o s s i b l e i n t h e r e f r a c t o r y i n o r d e r t o  drive the equi1ibriurn 2A1_ + 30 = A 1 0 2  3  (in the r e f r a c t o r y )  as m u c h a s p o s s i b l e t o t h e r i g h t . conforms almost  M a g n e s i urn -a Tumi n a t e  p e r f e c t l y to this description--apart, of  c o u r s e , from t h e mechanical  c h a r a c t e r i s t i c s p o i n t o f view,  w h i c h i s v e r y much a f u n c t i o n o f m a n u f a c t u r i n g Indeed,  technique.  t h e b e s t r e s u l t s w i t h s u p e r a l l o y s were o b t a i n e d  r e f r a c t o r i e s with high percentages The apparent  spinel  importance  by c o m p a r i s o n  w i t h T a y l o r 341  and,  of mechanical  with  of spinel. characteristics  o f the r e s i d u a l oxygen values  i s made obtained  Alundum 1139 i n t h e s u p e r a l l o y t e s t s .  65 Although  the former  c o n t a i n s some m o r e l o w e r s t a b i l i t y  the f a c t t h a t a dense complex allows the achievement Coralbond, stability  x  z  layer is  o x i d e s , e s p e c i a 1ly s i 1 i c a , hinders the  will,  any  possibility  c a s e , p r o m o t e e r o s i o n and  the b r i c k s p r e s e n t l y used  i n VIM,  i n t o the  In  when  kept  introduce  melt.  In o r d e r t o a c h i e v e will  de-S,  i t seems t h a t e i t h e r  be i n t r o d u c e d a n d  Earth treatments--or  with  lime mixtures  will  h a v e t o be u s e d .  such  accepted  by t h e  that less orthodox  users--  Volkov  I t i s e v i d e n t t h a t t h e use under  new  treatments,  as t h e one. d e s c r i b e d b y  r e f r a c t o r i e s w o u l d be i d e a l  of  (61)  lime  vacuum m e l t i n g c o n d i t i o n s ,  s i n c e t h e i r main m e t a l l u r g i c a l 1 i m i t a t i o n - - i n a b i 1 i t y to FeO  fluxing--is  problems time w i l l  removed under  before they w i l l  f u r n a c e on a r e g u l a r b a s i s . note tages  However, the and  be u s e d  in the p r o d u c t i o n  hydration  i n any  industrial  a s n o t i c e d by S c h l e g e l  VIM  I t i s e s p e c i a l l y i n t e r e s t i n g to p r e s e n t many  o f l i m e r e f r a c t o r i e s , a c t i n g as  b i n d i n g agent  resist  i t s e e m s t h a t some  t h a t t h e u s e o f c a l c i u m f l u o r i d e may  s i n t e r i n g and ance,  vacuum.  h a v e y e t t o be c i r c u m v e n t e d pass  in  degenera-  i n c l u s i o n s i n the melt.  in c o n t a c t with the a l l o y s in q u e s t i o n w i l l  techniques  lower  content.  lining, producing  a d d i t i o n , even  inclusions  of  of  use o f s i ags o r l i m e a d d i t i o n s t o the m e l t  in almost  t i o n o f the  formed,  In t h e c a s e  however, the c o n s i d e r a b l y higher content  5 f . :Jhe  as Rare  W  of very good r e s u l t s .  o f a c h i e v i n g a low o x y g e n  VIM  (Al CryTi )0  oxides,  and  improving  (78).  the h y d r a t i o n  advana resist-  66  Even  though  the chemical upgrading of the p r e s e n t l y  used r e f r a c t o r y b r i c k s would  be p o s s i b l e - - b y t h e u s e o f  (CaO + S i 0 ) p e r i c 1 a s e o r f u s e d MgO 2  grains i n s t e a d of the  p r e s e n t l y used p e r i c l a s e , f o r i n s t a n c e - - o n e would likely  t o f i n d e r o d e d g r a i n s and i n c l u s i o n s  still  in the  i.e.,  emphasis  s h o u l d be p l a c e d on p o u r i n g  of  concerned,  facilities,  the c o r r e c t s e l e c t i o n of p o u r i n g t e m p e r a t u r e s ,  d e s i g n and c o n s t r u c t i o n , time i n the l a d l e .  be  metal.  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R e f r a c t o r i e s ( 1 9 7 0 ) , 39  (Ogneupory)  O ' H a r a , M . H . , Duga, J . J . and S h e e t s , B u l l . , 5_i, No. 7 , ( 1972) , 590  J r . , H.D.,  No.l, Cer.  K h o r o s h a v i n , L . B . , D o l g i k h , G.V. and V.M. U s t y a n t s e v , R e f r a c t o r i e s ( O g n e u p o r y ) , N o . 8 , ( 1 9 7 0 ) , 509 M a s s , V . H . and A b r a t i s , H . , A r c h i v wesen , 4JD, ( 1969 ) , 153 Sveshkov, Y u . V . , K a l m i k o v , V.A. Me t a l l . , N o . 4 , ( 1972) , 29 K u l i k o v , I.S., "Deoxidation Moscow, (1975)  f u r das  and A g e y e v ,  of M e t a l s " ,  EisenhuttenP.Ya.,  Rus.  Metallurgya,  K a p p m e y e r , K.K. and H u b b l e , D.H., i n " H i g h T e m p e r a t u r e O x i d e s " , p a r t I, A l p e r , A . M . , (e d. ) , vAcademi c P r e s s , New Y o r k , ( 1 9 7 0 ) , 2. White,  J . , ibid,  Schlegel,  E.,  77  East  Ger.  Patent 59,500,  Jun 2 5 ,  1966  73  FIGURES  74  h/Miins.  boiling  surface tion  d e s o r p  free oxygen uptake  t(min)  Fig.  1 Theoretical  deoxidation  diagram  (8)  75  Fig. 2  Deoxidation  Curves  (II)  76  —  —  019  i  t 15  i  30 i  1 -*  Fig. 3  i  I4.5  Dimensions of the c r u c i b l e s  used in the t e s t s  (mm).  Different wetting  behaviours  78  Spot infrared pyrometer Pyrex glass Rubber cork Dismantable Pyrex extension  -Brass joint  Quartz tube High alumina cement ( applied over Zr 0 ) 2  Zirconia felt Molten metal Crucible Water cooled HF coil Alumina rod Brassjoint  Vacuum gauge Baffle to diffusion pump rotary pump 8  DETAIL  Fig. 5  Experimental  'A'  Apparatus  valve  6  V a r i a t i o n i n c a r b o n c o n t e n t o f A-ISI 1095 melted in Tasil-X crucibles  steel  80  C  Fig.  7  I n t e r f a c e AISI 1095/Tasi1-X. a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) S i l i c o n X - R a y map  X2400  81  Fig. 8  M i c r o s t r u c t u r e o f T a y l o r 320. Secondary Electrons a) D r i e d a t 6 0 0 ° C b) F i r e d a t 1 0 0 0 ° C  X120,  82  phi  Fig. 9  I n t e r f a c e AISI 1095/Alundum 1162. x48 a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) S i l i c o n X - R a y map  Melt time 5 min.  83  Fig.  10  T y p i c a l m i c r o s t r u c t u r e o f a c e m e n t made Al 0 and CaF (CAF). X300. 2  a) b) c) d)  3  2  Backscattered Electrons O x y g e n X - R a y map A l u m i n u m X - R a y map C a l c i u m X - R a y map  from  d  c Fig.  11  Adherence t e s t .  I n t e r f a c e Magnel/CAF.  a) S e c o n d a r y E l e c t r o n s b) Magnesium X-Ray map c ) Aluminum X-Ray map d) C a l c i u m X-Ray map  X240  F i g . 12  V a r i a t i o n i n carbon c o n t e n t of AISI m e l t e d i n CAF c r u c i b l e s  1095  steel  Fig.  13  V a r i a t i o n i n carbon c o n t e n t of AISI m e l t e d i n A l u n d u m 1139 c r u c i b l e s  1095  steel  c Fig.14  T y p i c a l m i c r o s t r u c t u r e o f a c e m e n t made A l 0 and MgF ( S P 2 ) . X240 2  3  2  a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) M a g n e s i u m X - R a y map  from  Fig.  15  V a r i a t i o n i n carbon c o n t e n t of AISI m e l t e d i n SP2 c r u c i b l e s  1095  steel  89  C  Fig.  16  Adherence test. Interface Magnel/SP2 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map  X240  Fig.  17  V a r i a t i o n i n carbon c o n t e n t of AISI m e l t e d i n T a y l o r 341 c r u c i b l e s  1095  steel  Fig.  18  I n t e r f a c e AISI 1 0 9 5 / T a y l o r 341. X 40, S e c o n d a r y E l e c t r o n s  M e l t t i m e 15  min.  F i g . 19  V a r i a t i o n i n c a r b o n c o n t e n t o f A I S I 1095 s t e e l m e l t e d i n C o r a l b o n d o r T a s i l - X c r u c i b l e , as a f u n c t i o n o f th  c F i g . 20  I n t e r f a c e AISI 1095/Coralbond. X24 a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) S i l i c o n X - R a y map d) P h o s p h o r o u s X - R a y map  d  M e l t t i m e 15 m i n .  F i g . 21  Detail of altered Coralbond (Fig.20). a) S e c o n d a r y E l e c t r o n s b ) S i l i c o n X - R a y map c ) P h o s p h o r o u s X - R a y map  X60  95  F i g . 22  Alumina i n c l u s i o n s from Coralbond. Interface AISI 1095/Coral bond. X1000, Secondary E l e c t r o n s  F i g . 23  Equilibrium  A1 (K=2AJ_+ ?  30,  in Nickel  F i g . 24  I n t e r f a c e X-750/Magne1. X240 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map  M e l t t i m e 15 m i n .  b  c Fig.  25  Interface  X-750/Magne1, metal  a) S e c o n d a r y E l e c t r o n s b) Magnesium X-Ray map c) A l u m i n u m X-Ray map  removed.  X17  99  F i g . 26  Deoxidation  equilibria  i n a N i - 1 % A1  Alloy  100  F i g . 27  Dense l a y e r formed a t i n t e r f a c e X-750/Taylor X1000, B a c k s c a t t e r e d E l e c t r o n s  341  101  F i g . 28  M i c r o s t r u c t u r e of s l a g from d e s u l p h u r i z a t i o n treatment. X60, S e c o n d a r y E l e c t r o n s  102  C  F i g . 29  M i c r o s t r u c t u r e o f slag from d e s u l p h u r i z a t i o n X120 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i nurn X - R a y map  treatment.  e  F i g . 31  Cross s e c t i o n o f working face o f Magnel b r i c k ( F i g . 3 0 ) . X60 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map d) C a l c i u m X - R a y map e ) N i c k e l X - R a y map  b  c Fig.  32  Metal p e n e t r a t i o n i n Magnel b r i c k v i a CalciumAluminates. X480 a) S e c o n d a r y E l e c t r o n s b) N i c k e l X - R a y map c ) C a l c i u m X - R a y map  106  F i g . 33  Metal p e n e t r a t i o n i n Magnel b r i c k - - C a 1 c i u m - A l u m i n a t e c o n t a i n i n g T i t a n i u m and Z i r c o n i u m . X600 a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map  107  F i g . 34  Detail brick.  of a P e r i c l a s e grain i n Unused X1000, S e c o n d a r y E l e c t r o n s  Magnel  b  F i g . 35  P e r i c l a s e g r a i n i n U s e d M a g n e l b r i c k , 15mm working face. Secondary electrons. a) X60 b) X 6 0 0  from  109  b F i g . 36  C a l c i u m - a l u m i n a t e s on t h e w o r k i n g X480 a) S e c o n d a r y E l e c t r o n s b) C a l c i um X - R a y map  face of  Magnel  Fig.  37  S p i n e l l a y e r on t h e w o r k i n g f a c e a) S e c o n d a r y E l e c t r o n s b) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map  of Magnel  X60  Fig.  38  Macroinc1 usions i n p a r t i a l l y Superalloy. X200, Secondary  forged N i c k e l - b a s e d Electrons  112  b Fig.  39  Microstructure X1200.  o f Calcium-aluminate  a) S e c o n d a r y e l e c t r o n s b) T i t a n i u m X - R a y map  inclusion (Fi  c F i g . 40  Microstructure of spinel a) S e c o n d a r y E l e c t r o n s b) A l u m i n u m X - R a y map c ) M a g n e s i u m X - R a y map d) T i t a n i u m X - R a y map  d inclusion.  X600  114  F i g . 41  P i e c e o f u s e d Rammed l i n i n g .  XI  115  Fig.  42  T y p i c a l m i c r o s t r u c t u r e o f t h e r a m m e d l i n i n g 6cm f r o m t h e w o r k i n g f a c e . X20, Secondary electrons  116  F i g . 43  C r o s s s e c t i o n o f w o r k i n g f a c e o f rammed l i n i n g . X24 a) S e c o n d a r y E l e c t r o n s b ) M a g n e s i u m X - R a y map c ) A l u m i n u m X - R a y map d) T i t a n i u m X - R a y map e) N i c k e l X - R a y map  117  Fig.  44  I n c l u s i o n s f r o m rammed l i n i n g , I n t e r f a c e N i m o n i c 9 0 1 / rammed l i n i n g , X 8 0 , S e c o n d a r y E l e c t r o n s  118  F i g . 45  A l t e r e d r a m m e d l i n i n g (5mm f r o m i n t e r f a c e ) . Dark phase: s p i n e l ; gray phase: titanium rich; l i g h t phase: t i t a n i u m and c e r i u m r i c h . X400, Secondary Electrons  119  F i g . 46  U n a l t e r e d MgO g r a i n c l o s e t o w o r k i n g f a c e l i n i n g . X40, S e c o n d a r y E l e c t r o n s .  o f rammed  120  TABLES  OXIDE A1 0 2  C r  (h|  3  2°3  IN IRON 4. 3 X l O "  n  1. 1 X l O "  < Cr h  sio  2  (h  Ti0  2  (h .  s 1  !IN NICKEL  •  1. 5 X 1 0 "  4  1 4  8  ft  2. 2 X 10  •  2  h )  T ]  2. 2 X l O "  1 4  _5  1. 6 X 1 0  0  2. 8 X 1 0 '  - 6  6  2. 5 X 1 0 ~  6  3. 1 X l O "  8  0'  Mgo ( h  H g  3. 2 X 1 0 "  h ) o  TABLE I. S o l u b i l i t y p r o d u c t s and N i c k e l ( 3 )  of oxides  in iron  7  (2)  OXIDE  STEEL COMPOSITION OR ASSUMPTIONS  MgO  %C == 0.4%  P  %C == 0.4%  %Zr == 0 . 1 %  4.11 mm Hg  %c --= 0.4%  %A1 == 0 . 1 %  16.9  %Si == 0 . 2 5 %  1.95 a tm  Zr0  2  A1 0 2  Si 0  3  2  CaO  TABLE  = 0.4%  %c == 0.4%  CO  P  co •  Mg  Ca  PcO 3.86 mm Hg  mm Hg  0.68 mm Hg  2. P r e s s u r e s o f CO i n e q u i l i b r i u m w i t h d i f f e r e n t o x i d e s and s t e e l m e l t s a t 1600°C (From S c h a f f e r (10))  Ni  Al l o y  Si  Fe  Mn  Cr  Ti  Al  Co  Mo  B  Inconel  718  52.5  max. 0.06  max. 0.35  bal .  max. 0.35  19.  0.9  max. 0.6  max. 1.0  3.0  Inconel  X-750  bal.  0.04  0.3  7.0  0.7  15  2.5  0.9  0.5  0.3  limonic  Pk50*  bal.  0.03  max. 0.15  max. 2.0  max 0.1  19.5  3.0  1.4  13.5  4.2  0.007  901  bal  0.02 0.06  max. 0.4  bal  max 0.5  11.0 14.0  2.8 3.1  0.15 0.3  max. 1.0  5.0 6.5  0.01 0.02  bal  0.15 0. 20  max. 0.2  max 1.0  max 0.2  8.0 11.0  4.5 5.0  5.0 6.0  13, 17,  2 4,  0.01 0.02  Nimonic  l i m o c a s t Pk24 (IN 100)  *Simi1ar TABLE  3.  t o Was pa H o y Nominal  compositions  o f some Vacuum M e l t e d  Superalloys.  Zr  max. 0.003 0.03  max. 0.05  0.03 0.09  TABLE  4.  MATERIAL (REFRACT.)  Refractory SIZE OF FURN  ZIRCONIA or ALUMINA SILICA (KORUNDAL XD) or MAGNESITE -CHROME (GUIDON)  5. 2kg LAB.  MAGNEL or KORUNDAL XD  Practices  TYPE OF LINING  PRODUCTS  PRE-FIRED TO TEMP. OF BRICK MAKING OPERATION  D-979 A I S I 4340 A I S I 52100  27 ton PROD.  BRICK & MORTAR  LATROBE STEEL  MAGNESIA + ALUMINA (2%SiOj d.  200kg  RAMMED SINTERED (31600°C  Ni-base s uperal1oys Heat r e s . steels Aust n i ti c stee1s  ALUMINA -SILICA 95,60,42% A1 0  12kg  PRE-FIRED  %0.2C  2  3  n  II  LIFE AND/OR RESULTS  COMMENTS  A l l showed substanti al and c o m p a r able C losses both i n 1 s t & 2nd h e a t s . Oxygen c o n t e n t constant f o r each a l l o y .  Did not t r y K o r u n d a l XD w i t h 52100.  25-45  Backup l i n i n g : K o r u n d a l XD Working l i n i n g : K o r u n d a l XD Magnel  heats  heats  .".4 3  Decreasing Si pickup f o r d e c r e a s i ng Si 0 i n t h e 2  c r u c i b l e (and C cons.)  REFERENCE (28)  Some d e c r e a s e in C composition a f t e r 1st heat  MgO d e p l e t i o n i n t h e s u r f a c e and formation of sulphur r i c h 1 ayer  (29) ( 3 0 ) (31)  (22)  (24)  TABLE  4.  MATERIAL (REFRACT.)  (Cont'd) SIZE OF ' FURN.  TYPE OF LINING  PRODUCTS  MAGNESIA +ALUMINA (70/30)  7 ton  RAMMED WET/ GRAPHITE  Nickel alloys Stee1s (Carpenter Steel)  MAGNESIA  12kg  PROBABLY PRE-FlRE D  0.2%  ZIRCONIA (5% CaO)  15kg  ?  MAGNESIA  Also 100kg  LIFE AND/OR RESULTS 30 h e a t s  Steel  NiMo 1.5 Alloy  COMMENTS  REFERENCE (33)  STEADY STATE 0_ 5 ppm 10 ppm Zr + Si p i ckup  (6)  (34)  Mg + Fe + S i pickup Al + S i pickup  ALUMINA FUSED LIME  20kg  RAMMED SINTERED @2000°C  N i - Fe Alloys  MAGNESIA + ALUMINA 65/25 6%S i 0  50/150 kg  RAMMED  Fe-C m e l t s  44 h e a t s o r mo re 8 cycles to room temp.  Very e f f e c t i v e S i d e - O x . and de-S  (35)  S t e a d y S t a t e 0^ 12 ppm  (11)  2  (NORTON RM 1170)  ./cont'd  TABLE 4.  Cont'd SIZE OF FURN  TYPE OF LINING  MAGNESIA + ALUMINA Termax B3 Termax MG 10 ~75/20 5S i 0  350kg  RAMMED  SPINEL o r MAGNESIA or ALUMINA  10kg  MATERIAL (REFRACT.)  LIFE AND/OR RESULTS  PRODUCTS  COMMENTS  REFERENCE  Nickel Alloys (Mg/W) C deoxidation  (36)  0  Fe = Ni Ni-Fe-Mo Ni  For Pure I r o n b e s t de-Ox i n Alumina (3.6x 10-5 CxOJthen S p i n e l and then M a g n e s i a ( 1 6 x l O - C x 0)  (37)  5  Stee1s Superal1oys (Cameron I r o n )  MAGNEL  60t  BRICK & MORTAR  MAGNESIA  1 ton  RAMMED 20% Mo-Ni (PROBABLY) A l l o y Dai do Steel  MAGNESIA  250kg 5-10t  (38)  ::  (39)  Hastel1oy R-235 RAMMED  FIRTH-BROWN  (40) F i r i n g with  template  (41)  TABLE 4.  Cont'd  MATERIAL (REFRACT.)  SIZE OF FURN  MAGNESIA or MAGNESIAALUMINA or ALUMINA  TYPE OF LINING  PRODUCTS  RAMMED  Fe,Ni  alloys  1501000 kg  RAMMED (?)  MAGNESIA  6t  RAMMED  MAGNESIA  300kg  RAMMED  Ni a l l o y s Steels (Jessop & Sons)  500kg  RAMMED  Steels (Ke1seyHayes C o . )  RAMMED  Steels Ni-Alloys  MAGNESIA ALUMINA (70/30)  MAGNESIA or MAGNESIAALUMINA (66/25)  COMMENTS  Spinel ~3 5 heats 250-1000kg Magnesi a h a l f of the 1i fe of S p i n e l  ZIRCONIA or MAGNESIA  MAGNESIA , ALUMINA (70/30)  L I F E AND/OR RESULTS  REFERENCE  F i r i n g with template or g r a p h i t e c o r e - S t r e s s e s i n MgO a r e large  N i a 11 oy s , Steels (Special M e t a l s , 1957)  (5)  (42)  12 h o u r d ry i n g  vacuum  Firing with graphite @. 2000°C i s p r e f e r r e d since i t allows the r e f r a c t o r y t o be checked before use.  (43) (44)  (45)  ,  F i r i n g with template or g r a p h i t e c o r e . M a g n e s i a bonded by CaO + S i 0  (46)  2  M a g n e s i a - A l u m i n a by CaO + S i 0 + FeO 2  /conf d  TABLE 4. MATERIAL (REFRACT.)  Cont'd SIZE OF FURN.  TYPE OF LINING  KORUNDAL XD CORALBOND  BRICK and MORTAR  MAGNEL CORALBOND  BRICK and MORTAR  PRODUCTS  L I F E AND/OR RESULTS  REFERENCE  COMMENTS  7 heats of Ni-superal1oy Severe e r o s i o n i n the j o i n t s Better results than w i t h KORUNDAL XD CORALBOND  (47)  (47)  MAGNEL PE RIBON D  lot  BRICK and MORTAR  Stee1s (Armco Research)  15-20 h e a t s (Cyclic ope r a t i on)  Fai1ure occurs in the bottomTop l a y e r o f b r i c k s b u l g e s up. B a c k u p i s KORUNDAL XD  (48)  SPINEL BRICK or MAGNESITECHROMITE BRICK or ALUMINA BRICK  10 to 30t  BRICK and MORTAR  Stee1s,  20-45 h e a t s  MAG-CHROMITE b r i c k has 65%MgO/13% CrO /8%Al 0  (49)  ALUMINA or SPINEL  <2.5 t  Stai nless Tool Supe r a 1 1 o y s  Q  9  q  Alumina b r i c k 10% S i 0  has  2  Importance of mortar j o i n t s RAMMED  Ni , Co, Fe , AlToys  Spinel is to l O t  used up  (50)  .../cont'd  ™  TABLE 4. MATERIAL (REFRACT. ) ALUMINA or SPINEL  Cont'd SIZE OF FURN >2.5t lOt 25t 60t  TYPE OF LINING BRICK and MORTAR  PRODUCTS  L I F E AND/OR RESULTS Good  COMMENTS  REFERENCE  Cement T a y l o r 3 4 1 * Back L i n i n g MULLITE BRICK w i t h N a S i 0 3  bonded s i l i m a n i t e (TAYLOR 320)  (50)  MATERIAL  C  Mn  Si  Cr  N i c k e l vac X - 7 5 0 *  0.067  0.08  0.04  13.55  A I S I 1095 (nomi na1)  0.96**  0.40  0.30  -  * Analysis **Analysed TABLE  5.  by T e 1 e d y n e - A l 1 vac a t UBC Composition  of metals  used i n the  tests  Ti  Al  Fe  Ni+Co  2.58  0.71  7.75  71.35  bal.  MATERIAL  MgO  Magne1  89..8  A 1  2°3 8. 3  Alundum 1139  99.  Alundum 1163  81.  Cora 1 bond P e r i bond 320  Taylor  341  Tasil  X  TABLE  6.  2  0. 7  P  2°5  -  0., 7 12.  C  a  0  F e  2°3  Others  -  0.,9  0.. 3  0., 1  0.. 1  Na 0--  0., 3  0.,4  1.. 3  Ti0 --  5. 3. 1  2  2  0., 1  79. 3  6., 7  9.1  0., 1  1.. 5  Ti0 --  78..8  2. 4  14., 7  -  0.. 1  0..8  A l k a l i e s - -2. 2  10.  -  0., 10  0.,10  A l k a l i e s - - 2 . 30  0..02  Taylor  S i 0  87. 95 .  0.. 1  55.  Typical chemical a n a l y s i s materials tested.  0..02 40.  0..03  4.5  -  2  0., 1  A l k a l i e s - - 2 ., 7  •1.0.  {% , a c c o r d i n g t o s u p p l i e r s )  of  refractory  OXYGEN CONTENT  MATERIAL SP2  17  MAGNEL  22  TAYLOR 341  28  PERIBOND  37  CAF  41  ALUNDUM 1139  46  CORALBOND  60  X-750 as  TABLE 7.  received  (PPM)  7  Oxygen c o n t e n t o f X-750 a f t e r 15 m i n . h o l d i n g t i m e a t 1500°C i n d i f f e r e n t refractory materials.  

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