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Removal of calcium containing inclusions during vacuum arc remelting Samuelsson, Eva 1983

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REMOVAL OF CALCIUM CONTAINING INCLUSIONS DURING VACUUM ARC REMELTING by EVA SAMUELSSON M.Sc,  Royal I n s t i t u t e Of Technology, Stockholm, 1981  A THESIS SUBMITTED  IN PARTIAL FULFILMENT OF  THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department Of M e t a l l u r g i c a l  Engineering  We accept t h i s t h e s i s as conforming to the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA November 1983  ©  Eva Samuelsson,  1983  In  presenting  this  thesis  in  partial  fulfilment  of  the  requirements for an advanced degree at the U n i v e r s i t y  of  British  Columbia,  I  it  freely  available  for  permission  agree  for  purposes may or  her  that  the  Library  shall  reference  and  study.  I  extensive  be granted by the Head of my It  of t h i s t h e s i s  allowed without my  Department of  written  for  is  1983  understood  permission.  Metallurgical  November  agree  Engineering  gain  that  that  scholarly  Department or  financial  The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V 6 T 1W5  Date: 15  further  copying of t h i s t h e s i s f o r  representatives.  publication  make  by  copying  shall  not  his or be  i i  Abstract The  mechanism  of removal of c a l c i u m c o n t a i n i n g i n c l u s i o n s  i n s t e e l d u r i n g Vacuum Arc Remelting Laboratory remelting the  Electron  electrodes  steels  were  Beam  and  has been i n v e s t i g a t e d .  and  industrial  Vacuum  i n g o t s were examined.  determined  with  the  aid  of  Arc  P r o p e r t i e s of chemical  and  m e t a l l o g r a p h i c methods. It  is  proposed  that  the  major  mechanism of removal i s  r e j e c t i o n of c a l c i u m aluminates to a f r e e s u r f a c e .  One  the c a l c i u m s u l p h i d e i s r e j e c t e d with the  aluminates.  The  remainder  reacts  with  aluminium  calcium  oxide i n the  t h i r d of  aluminates  a c c o r d i n g to the f o l l o w i n g r e a c t i o n :  CaS  + 1/3A1 0 = CaO 2  3  Subsequently, dissolved  the  + 2/3[Al] + [S]  calcium  sulphur  oxide  is  also  rejected  and  the  r e a c t s with s u l p h i d e forming elements d u r i n g  solidification. The 5-10  final  ppm,  was  calcium  content  of  the  of  the  calcium  content  study  are  not  agreement  independent  remelted  steels, of the  electrode. The previous  results work,  of  this  which  the c a l c i u m aluminates sulphur,  aluminium  attempts  with  to e s t a b l i s h the composition  as a f u n c t i o n of  and c a l c i u m .  in  the  steel  Specifically  content  of of  i t i s found that  iii  the  influence  sufficiently  of  oxygen  content  taken i n t o account.  has  not  previously  been  iv  Table of Contents Abstract L i s t of Tables L i s t of F i g u r e s Acknowledgements I. INTRODUCTION 1 .1 O b j e c t i v e s 1 .2 Methods II. LITERATURE REVIEW 2.1 Ladle Treatment Of S t e e l 2.1.1 L a d l e I n j e c t i o n 2.1.2 Wire I n j e c t i o n 2.1.3 Conventional A l l o y A d d i t i o n 2.2 Remelting Under Vacuum 2.2.1 Vacuum Arc Remelting 2.2.2 E l e c t r o n Beam Remelting 2.3 I n c l u s i o n Shape C o n t r o l 2.3.1 I n c l u s i o n M o d i f i c a t i o n With Calcium 2.4 Thermodynamic P r o p e r t i e s 2.4.1 Calcium Metal 2.4.2 Calcium In S t e e l 2.4.3 Calcium Aluminates 2.4.4 Calcium Sulphide 2.5 Evaporation Rate III. EXPERIMENTAL PROCEDURES .' 3.1 Samples •. 3.1.1 I n d u s t r i a l Samples 3.1.2 Laboratory Samples 3.2 A n a l y s i s 3.2.1 M e t a l l o g r a p h i c Examination 3.2.2 Bulk S t e e l Composition 3.2.3 I n c l u s i o n E x t r a c t i o n IV. RESULTS AND DISCUSSION 4.1 Thermodynamic C o n s i d e r a t i o n s 4.2 E l e c t r o n Beam Remelting 4.3 I n d u s t r i a l VAR Samples 4.4 General Observations Related To Calcium Treated Steels 4.4.1 Calcium Aluminate Composition 4.4.2 I n c l u s i o n s In The L i q u i d S t e e l V. CONCLUSIONS  i i v vi vii 1 3 3 4 4 5 6 6 7 8 10 11 12 18 18 18 20 22 22 24 24 24 24 27 27 28 29 30 30 34 35  BIBLIOGRAPHY APPENDIX A - NOTATION APPENDIX B - DETERMINATION OF CALCIUM IN STEEL BY ATOMIC ABSORPTION SPECTROPHOTOMETRY APPENDIX C - STEEL COMPOSITIONS APPENDIX D - UNCERTAINTY OF CHEMICAL ANALYSIS  40 41 42 45 47 51 52 53 54  V  List  1. 2. 3. 4.  5.  of  Tables  VAR m e l t i n g c o n d i t i o n s EB r e m e l t i n g c o n d i t i o n s D e s c r i p t i o n of the h y p o t h e t i c a l s t e e l Summary of a n a l y s i s . Vx marked s a m p l e s denotes e l e c t r o d e s t e e l s , and VxR marked samples a r e corresponding remelted ingots R e s u l t s of mass b a l a n c e s  24 l l 33  38 39  vi  List  1. 2.  of  Figures  S c h e m a t i c o u t l i n e o f t h e VAR p r o c e s s Crown r e g i o n of a VAR i n g o t w h i c h c o l l e c t s inclusion m a t e r i a l f l o a t e d to the ingot p e r i p h e r y S t a n d a r d f r e e e n e r g y o f f o r m a t i o n of some o x i d e s important in steelmaking S t a n d a r d f r e e e n e r g y of f o r m a t i o n o f some sulphides important in steelmaking S c h e m a t i c r e p r e s e n t a t i o n of m o d i f i c a t i o n of inclusions with Ca-treatment . ... The p s e u d o b i n a r y c a l c i u m o x i d e — a l u m i n i u m o x i d e phase d i a g r a m " C o m p o s i t i o n of c a l c i u m a l u m i n a t e s as a f u n c t i o n of steel calcium content. H i l t y and F a r e l l , --Haida e t . a l . The p s e u d o b i n a r y c a l c i u m s u l p h i d e — manganese sulphide phase d i a g r a m Diamond pyramid hardness versus temperature for some(Mn,Ca)S s o l i d s o l u t i o n s Schematic f i g u r e showing where samples and electrodes f o r EB m e l t i n g were c u t f r o m i n d u c t i o n f u r n a c e ingots. 8  8  3. 4. 5.  1  6.  4  7.  2  2  8.  2  2 5  9.  2  10.  5  8 9 13 13 14 16  1  16 17 17  26 11.. 12.  13. 14.  The E l e c t r o n Beam f u r n a c e a t UBC 26 Schematic d e s c r i p t i o n of the problems w i t h microprobe analysis. Note that a l l three i n c l u s i o n s give the same a p p e a r a n c e f r o m t h e s u r f a c e 28 E v a l u a t i o n of the thermodynamic d r i v i n g f o r c e . 34 "Bead" of c o a l e s c e d i n c l u s i o n s c o l l e c t e d from surface of E B - m e l t e d i n g o t . The b l a c k p a t c h e s a r e CaS and t h e bulk phase i s C A .36. X - r a y s p e c t r u m s showing the r e l a t i v e c o m p o s i t i o n of an i n c l u s i o n i n an e l e c t r o d e s t e e l and corresponding inclusion "bead" 36' C o a l e s c e d i n c l u s i o n s on an e l e c t r o d e t i p . Light m i c r o s c o p e a n d SEM X - r a y i m a g e s 37 C o m p o s i t i o n of c a l c i u m a l u m i n a t e s as a f u n c t i o n of steel calcium content. Experimental results, and r e s u l t s from H i l t y & F a r e l l and H a i d a 41* I n c l u s i o n in pinsample taken from the l i q u i d steel. L i g h t m i c r o s c o p e a n d SEM X - r a y i m a g e s ,43 x  15.  16.  y  r  17.  2  18.  1  2  2  vi i  Acknowledgement  I  would  like  to thank Dr Alec M i t c h e l l f o r h i s  guidance and time spent on many h e l p f u l d i s c u s s i o n s . The c o n t r i b u t i o n of  samples  from  my  colleagues  i n the  i n d u s t r y was e s s e n t i a l f o r the p r o j e c t and i s much a p p r e c i a t e d . The  assistance  of  the  t e c h n i c a l s t a f f at the M e t a l l u r g y  department, p a r t i c u l a r l y Gus S i d l a , Rudy Cardeno, Mary Mager and Laurie Frederick  i s g r a t e f u l l y acknowledged.  I would a l s o l i k e to thank my f e l l o w gratuate their  students  for  f r i e n d s h i p and many i n t e r e s t i n g d i s c u s s i o n s . Economic  a s s i s t a n c e from the N a t u r a l  Sciences  and Research  C o u n c i l of Canada i s g r a t e f u l l y acknowledged. Finally  I would l i k e to thank my husband, Fred Bradley, f o r  h i s encouragement and many h e l p f u l  suggestions.  1  I. The  production  INTRODUCTION of  quality  a p p l i c a t i o n s , such as a i r c r a f t  landing  control  of  metallic  i n c l u s i o n s , and m e t a l l u r g i c a l  ensure  hydrogen  steels  mechanical  Arc Remelting  and  Two  Electro  ESR  process  is  tight  in  non-  order  to  r e m e l t i n g processes, Vacuum Remelting  (ESR),  are  steels.  c h a r a c t e r i z e d by the r e m e l t i n g of an  e l e c t r o d e through a r e f i n i n g conditions.  requires  structure  Slag  commonly used to manufacture these The  gears,  demanding  content, q u a n t i t y and composition of  soundness.  (VAR)  for  slag, generally  under  atmospheric  An advantage of the process i s that the content  and  nature of the n o n - m e t a l l i c i n c l u s i o n s can be c o n t r o l l e d , to some extent,  through  manipulation  of  the slag-metal r e a c t i o n s .  d e s i r a b l e m e t a l l u r g i c a l s t r u c t u r e can be a t t a i n e d by the  rate  mould.  of  ingot  solidification  S p e c i a l p r e c a u t i o n s must  monitoring  i n the water-cooled  be  taken  to  A  avoid  copper  hydrogen  pick-up d u r i n g r e f i n i n g . In North America, that  many  process. electrode  of  these  for h i s t o r i c a l steels  In c o n t r a s t to the ESR is  remelted  under  b e n e f i t of a r e f i n i n g s l a g . hydrogen c o n t e n t . ingot  must  be  produced  vacuum  conditions  Due  process without  VAR an the  The vacuum p r o c e s s i n g ensures a low to  the  ESR  process,  the  s t r u c t u r e can be c o n t r o l l e d , although the  r e m e l t i n g r a t e i s not as e a s i l y monitored instability.  u s i n g the  process, i n the VAR  In a s i m i l a r way  solidification  reasons, r e g u l a t i o n s s t a t e  to the lack of s l a g  due  to problems of arc  refining,  the  electrode  2  material  must  be  w e l l d e s u l p h u r i z e d p r i o r to r e m e l t i n g , s i n c e  vacuum r e a c t i o n s do not r e s u l t  to  in s i g n i f i c a n t desulphurization.  Many techniques  f o r the d e s u l p h u r i z a t i o n of  casting  VAR  the  electrode,  are  steels,  available.  t r a d i t i o n a l l y d e s u l p h u r i z a t i o n i n the e l e c t r i c a r c been  used  for this  purpose,  the  prior  recent  While  furnace  trend  has  i s to l a d l e  d e s u l p h u r i z e with calcium or c a l c i u m - c o n t a i n i n g compounds. advantages a s s o c i a t e d with l a d l e treatment production  at  lower  are i n c r e a s e d  furnace  provides  addition inclusion  Although lost  during  of  shape  remelting,  the  the  control  calcium  treatment  electrode  steel.  that much of the calcium i s  treatment  is  known  to  From the apparent  be  Almost  s t e e l as e i t h e r  contradiction  one  could  c o n c l u s i o n that d e l e t e r i o u s elements a r e removed with  calcium  explanation, mechanical  sulphide other  has  mechanisms  While been  stochiometric  evaporation  suggested  a  possible  operate,  for  instance  flow.  Finally,  from an  could  removal by buoyancy or f l u i d  economic p o i n t of view the q u e s t i o n a r i s e s content  pick-up.  c a l c i u m i s bound i n the s o l i d i f i e d  the c a l c i u m d u r i n g r e m e l t i n g . of  f o r the  accepted calcium  the  without  f o r the mechanical p r o p e r t i e s of the product.  s u l p h i d e or oxide. draw  desulphurization  i t i s commonly  beneficial all  to  levels  steelmaking  the dangers of phosphorus r e v e r s i o n or aluminium In  furnace  c o s t and d e s u l p h u r i z a t i o n to lower  than are p o s s i b l e i n e l e c t r i c arc  The  of  calcium  as  as  to  i n the e l e c t r o d e has a d i r e c t  the s t e e l q u a l i t y a f t e r r e m e l t i n g .  Since c a l c i u m  whether  the  i n f l u e n c e on treatment  is  3  an  expensive  process  extensive  precautions  casting,  i t  calcium,  i s  and  the  to prevent  advantageous  a n d i n what  presence  form,  of  reoxidation to  define  calcium requires during  precisely  electrode how  much  i s required i n the electrode.  1.1 O b j e c t i v e s  The removal study  major  mechanism the  final  study  are  to  determine  o f c a l c i u m d u r i n g Vacuum A r c R e m e l t i n g ,  influence  of  ingot composition,  composition 1.2  o b j e c t i v e s of t h i s  the  and t o  electrode calcium content  particularly  of calcium-containing  as  i t  relates  the  on t h e to  the  inclusions.  Methods  Industrial remelted steels  VAR  samples have have  metallographic  The reactions  been  samples been  and  laboratory  investigated.  determined  with  the  Electron  Properties aid  of  of  chemical  Beam the and  methods.  thermodynamic was d e t e r m i n e d  driving  force  to interpret  for  potential  chemical  the experimental  evidence.  4  II.  LITERATURE REVIEW  2.1 Ladle Treatment Of S t e e l The  increased  demand  for  high  quality  i n t r o d u c t i o n of the U l t r a High Power e l e c t r i c BOF  processes  secondary  steels,  furnaces  used in c o n j u n c t i o n with continuous  steelmaking  more  attractive  for  the  procedures  have  Here, only those processes w i l l be  the  steelmaking  As a r e s u l t , a l a r g e number of secondary developed  and  c a s t i n g make  companies.  been  the  steelmaking  d u r i n g the l a s t twenty y e a r s .  which are used f o r calcium  treatment  discussed.  The  two  major purposes of c a l c i u m treatment  desulphurization  and  desulphurization sulphur.  The  the s l a g .  is  inclusion due  resulting  to  control.  In a d d i t i o n ,  the  calcium The  The  high a f f i n i t y of c a l c i u m f o r  i n c l u s i o n s are l i g h t and  sulphur c a p a c i t y of the s l a g . treatment,  the  shape  of s t e e l s are  treatment  float easily increases  to the  second consequence of c a l c i u m  i n c l u s i o n shape c o n t r o l , w i l l be d i s c u s s e d i n s e c t i o n  2.3. The  physical  properties  vapour pressure at steelmaking simple  addition  methods  more e l a b o r a t e techniques injection calcium  have  been  of c a l c i u m , temperatures,  prevent  the use  of pure c a l c i u m to s t e e l . such  as  developed.  in the form of an  low d e n s i t y and  alloy.  powder  injection  Another a l t e r n a t i v e  high of  Therefore, and  wire  i s to add  5  The  low  solubility  of  calcium  in  steel  may  also  cause  problems.  With the more s o p h i s t i c a t e d a d d i t i o n techniques  possible  to  reach  d e s u l p h u r i z a t i o n and must  contents inclusion  high  enough  shape  for  control.  i t is  satisfactory However,  care  be taken not to r e o x i d i z e the s t e e l during teeming to such  an extent that the i n c l u s i o n shape c o n t r o l d i m i n i s h e s . 2.1.1 Ladle  Injection  Holappa injection  1  has  summarized the p u b l i s h e d work concerning  metallurgy.  Ladle i n j e c t i o n , which i s the developed  mainly  as  a  rapid  newest  ladle  desulphurization  process,  was  method.  The  process a l s o p r o v i d e s a means to i n t r o d u c e c a l c i u m i n the with subsequent d e o x i d a t i o n and  connected  to  a  lance  can  gas,  injected advantages  usually  deeply with  into  stirring  that  the  ladle  are given s u f f i c i e n t principal  argon.  the  steel.  but  it  also  with the l a d l e l i n i n g .  steel.  ladle  one  of  a  i s then  the  main  i s that l i g h t a l l o y a d d i t i o n s r e a c t with the s t e e l .  injection  causes.  advantage of c r e a t i n g a l a r g e c o n t a c t slag,  dispensers  i n the d i s p e n s e r by  Thus,  time to melt and  injection  powder  The powder — gas mixture  injection  f e a t u r e of  of  be immersed i n t o the  i n j e c t i o n , the powder i s f l u i d i z e d  carrier  second  that  steel,  i n c l u s i o n shape c o n t r o l .  The equipment f o r i n j e c t i o n c o n s i s t  During  ladle  The area  is  the  vigorous  stirring between  The  has  steel  the and  causes problems with r e o x i d a t i o n r e a c t i o n s Therefore  ladles  used  for  injection  6  treatment  are  lined  with  highly  stable refractories  dolomite, magnesite and high alumina. the  most  calcium  carbide  (~80%  of CaO,  Wire An  CaF  CaC )  and  2  2  and  different  to  2  wire  speed  with  a steel layer,  (80-300  steelmaking 1-3  2 ,  3>  m/min)  the  *.  into  the  The  Economically,  powder  wire  steel.  the  prevented i s fed  Less than  the b o i l i n g of  Since the s t e e l c l a d  system  i s wire  protecting  the c a l c i u m can be  at  1.5  m  calcium  wire w i l l  melt  permits l i q u i d c a l c i u m to r e a c t  with the s t e e l before e v a p o r a t i o n of remaining  wire  mixtures  technique  By  with a i r or s l a g .  temperatures.  seconds,  investment  Ca),  3  f e r r o s t a t i c head i s r e q u i r e d to suppress  in  slag  the powder i n j e c t i o n  from r e a c t i n g prematurely  at  (~30%  Al 0 .  " i n j e c t i o n " of c a l c i u m i n t o the l a d l e  high  treatment,  Injection  alternative  calcium  calcium  commonly used powders are c a l c i u m s i l i c i d e  consisting 2.1.2  For  such as  injection  demands  whereas the c o s t per added u n i t  calcium a  higher  occurs. initial  c a l c i u m i s higher f o r  "injection".  2.1.3  Conventional A l l o y A d d i t i o n Calcium has c o n s i d e r a b l y higher s o l u b i l i t y  nickel  than  in  iron.  in  silicon  and  T h i s f a c t a l l o w s the p r o d u c t i o n of high  c a l c i u m a l l o y s which are l a t e r used f o r adding c a l c i u m t o s t e e l . As the a c t i v i t y of c a l c i u m reactions  is  lowered  in  with s t e e l become l e s s v i o l e n t ,  i s obtained.  A s e r i o u s disadvantage  these  alloys,  and a higher  of t h i s kind  of  the  recovery treatment  7  i s the i n t r o d u c t i o n of a d d i t i o n a l elements, be  desirable.  Therefore,  m e t a l l i c calcium technique  is  covered  the  some by  violent  which may  companies  steel.  The  reaction  that  even add problem occurs  amounts of c a l c i u m come i n contact with the 2.2 Remelting  not always " l o g s " of with  this  when l a r g e r  steel.  Under Vacuum  At present, two processes are a v a i l a b l e f o r r e m e l t i n g under vacuum. (EB)  These are Vacuum Arc Remelting  melting.  then the VAR  and EB m e l t i n g processes are very s i m i l a r .  the molten metal  i m p u r i t i e s are removed by  is  vacuum a r c . generally input. VAR  the  heat  Krone,  5  processes.  alloying  materials. more d e t a i l .  structure.  pressure  the m e l t i n g speed  Kazakov  6  and W a h l s t e r  In both exposure  solidification  The  fundamental .  7  in  the  EB  process  independent  is  of the power  have compared the EB  and  The c o n c l u s i o n of t h e i r comparison i s that due  to the slower m e l t i n g speed more  Beam  sources, e i t h e r an e l e c t r o n beam or a  In a d d i t i o n the lower, and  the  to vacuum and the continuous  ensures a - c o n t r o l l e d s o l i d i f i c a t i o n difference  and E l e c t r o n  I f the EB furnace i s c o n s t r u c t e d f o r r e m e l t i n g ,  processes some chemical of  (VAR)  elements  The EB and VAR  the EB melted  and  impurities  materials  will  than  VAR  processes w i l l now  the be  lose melted  discussed  in  8  2.2.1 Vacuum Arc Remelting The  Vacuum  Arc  o u t l i n e d i n Figure  Remelting  process  a  8  DC power supply,  connected  i s given  by  to  a  vacuum  pumping  machinery to move the e l e c t r o d e and  control instrumentation.  the VAR process  i s schematically  1 . The equipment c o n s i s t s of a water-cooled  copper c r u c i b l e , an enclosure system,  (VAR) process  A more d e t a i l e d d e s c r i p t i o n of  Mitchell . 8  During  remelting  an  electric  a r c between ingot and e l e c t r o d e s u p p l i e s the heat f o r  melting.  Molten drops from the e l e c t r o d e t i p s u c c e s s i v e l y  i n t o the l i q u i d p o o l , and heat removal f o r s o l i d i f i c a t i o n through  the  solidified  i m p u r i t i e s by evaporation  ingot  and c r u c i b l e .  i s possible  e l e c t r o d e t i p and the molten p o o l .  from  occurs  Thus, removal of  two  surfaces,  the  In a d d i t i o n , s o l i d or l i q u i d  DC. Power Supply  Vacuum Pump  Water in  Figure  fall  1 - Schematic o u t l i n e of the VAR  process . 8  9  i m p u r i t i e s c a n be removed by t h e f l u i d f l o w a n d / o r the molten p o o l Krone discussed during  t o t h e s u r f a c e of t h e  et.al. ,  Povolotskii  5  the removal  of  non-metallic removed,  by  i n c l u s i o n s on t h e either  et.al. , 9  floating  containing  Povolotskii are  9  ingot  are  8  from that  9  have steel the  mechanically  t o t h e edge of t h e p o o l o r b e i n g  edge  VAR  inclusions  surface  of the i n g o t .  a  Mitchell  8  s p l a t t e r e d on t h e "crown" of  and  I t h a s been s u g g e s t e d ' pool  from  ingot.  non-metallic  Vacuum A r c R e m e l t i n g .  buoyancy  a l s o found t h a t u n s t a b l e  Figure  2 shows t h e  non-metallic inclusions  top  inclusions. such  as  Si0  2  r e d u c e d by c a r b o n b u t t h a t c o r u n d u m i s n o t a f f e c t e d . The  pressure  at  the  m o l t e n s u r f a c e s c o u l d be a s much a s  Figure 2 - Crown r e g i o n o f a VAR i n g o t w h i c h c o l l e c t s i n c l u s i o n m a t e r i a l f l o a t e d to the ingot p e r i p h e r y . 8  10  three orders of magnitude higher than that measured at the of  the  pumping  system .  T h i s i s reasonable, s i n c e the vapour  5  p r e s s u r e of i r o n alone  i s an order of magnitude higher at 1600°C  than the " o p e r a t i n g p r e s s u r e " of 1X10~  — 5X10"  3  torr.  3  a l s o known that Mn, which at r e m e l t i n g temperature s o l u t i o n , not as s u l p h i d e , does evaporate 2.2.2 E l e c t r o n Beam As  difference  1 0  .  which  furnace.  The  Apart  to a l a r g e extent.  The EB process has been d e s c r i b e d  from the the  two  lower  heat  10~  chamber the  source,  processes  i s around  s t a b l e o p e r a t i o n of 10""  source.  between  pressure,  i s present i n  the p r i n c i p a l d i f f e r e n c e between VAR and EB  i s the heat  by S c h i l l e r  It i s  Remelting  mentioned,  remelting  head  2  torr  the  other  i s the m e l t i n g chamber f o r an  industrial  pressure i s maintained  gun,  which  major  requires  a  EB  to assure  pressure  of  t o r r or lower. The  removal  of  d i s c u s s e d by Krone manganese  and  5  a l l o y i n g elements and i m p u r i t i e s has been  and D o e n e c k e . 11  sulphur  are  Doenecke  suggests  11  that  removed by e v a p o r a t i o n , and oxygen  a c c o r d i n g to the r e a c t i o n  [C] + [0] = CO(g).  However, he does not, by results, sulphur.  prove  the  either  mechanisms  calculations  or  experimental  of removal of e i t h e r oxygen or  11  The  removal mechanism of n o n - m e t a l l i c  d u r i n g EB melting has literature.  i n c l u s i o n s from  not been d i s c u s s e d in any  However, EB-melting  detail  steel  in  the  has been used f o r n o n - m e t a l l i c  i n c l u s i o n assessment of s u p e r a l l o y s 12  1 3  .  This  technique  is  based on the f a c t t h a t the l i g h t  i n c l u s i o n s f l o a t to the s u r f a c e  of  l a t e r be c o l l e c t e d .  the  ingot  where  they  can  c l a i m s that the alumina i n c l u s i o n s can be recovered last  1 — 2 ppm  Sutton down to  1 3  the  using t h i s method.  2 . 3 I n c l u s i o n Shape C o n t r o l The well  morphology and composition'of  as  their  influence  on  mechanical  d e s c r i b e d by s e v e r a l a u t h o r s " " . 1  steel  is  directly  grade  steels  Unfortunately,  are  related fully  the  indigenous  The  1 6  inclusions,  p r o p e r t i e s , has been  inclusion picture  of  to the deoxidati.on p r a c t i c e .  killed,  aluminium  u s u a l l y ' with oxide  i n c l u s i o n s which f r e q u e n t l y gather  as  forms  in c l u s t e r s .  a  High  aluminium. hard,  angular  These  alumina  c l u s t e r s can be d e l e t e r i o u s f o r the mechanical p r o p e r t i e s of  the  steel.  In  the  formation  of manganese s u l p h i d e type I I .  adverse  influence  addition,  of  aluminium  alumina  deoxidation  utilize  titanium.  However, i n a l l cases  usually  performed  a  clusters  a l t e r n a t i v e d e o x i d a t i o n p r a c t i c e s have practices  As  been  promotes result  and  with aluminium.  y i e l d of the expensive  elements which  modification.  only  Here,  the  type II  MnS  developed.  c a l c i u m , the rare e a r t h metals, initial  of  ladle  These  zirconium or  deoxidation  is  T h i s p r a c t i c e i n c r e a s e s the are  used  for  inclusion  i n c l u s i o n m o d i f i c a t i o n with  calcium  12  w i l l be d i s c u s s e d . 2.3.1  I n c l u s i o n M o d i f i c a t i o n With Calcium Calcium  i s among the s t r o n g e s t oxide and  of  the  elements  it  will  modify  formation  of  as can be seen existing  MnS  i n F i g u r e s 3 and  oxides  type I I .  sulphide  and  it  4.  also  formers  Therefore,  prevents  the  The change i n i n c l u s i o n morphology  and composition between an untreated and a c a l c i u m t r e a t e d is schematically i l l u s t r a t e d  steel  i n F i g u r e 5.  D i f f e r e n t e x p l a n a t i o n s have been given f o r the mechanism of formation MnS  of  type I  the  three  inclusions  types  are found  and are of a s p h e r i c a l shape. it  forms by a monotectic  during  of  solidification.  MnS  in  r e a c t i o n i n the  interdendritic  the  metal  the  mechanical  formed indicate MnS  by  an that  type I I I  promoted  it  p r o e u t e c t o i d phase.  inclusions  form  but  later  region and When almost  are  that the  angular  reaction. is  such as C, Cr, Ca and excess A l .  It  elements  being that MnS  the  assumed  formation  alloy  and  for  investigations  forms by a c o o p e r a t i v e monotectic  result  that  steels.  T r a d i t i o n a l l y , type II was  reaction,  by a l l o y elements  the  type II  change  the  phase  i s p r e c i p i t a t e d as a s o l i d  In that case the i n c l u s i o n s would f l o a t  of the melt l i k e other l i g h t  .  steels  which are p a r t i c u l a r l y d e l e t e r i o u s  inclusions  has been suggested diagram,  the  properties. eutectic  1 9  i n c l u s i o n s are r o d l i k e  i n c o l o n i e s as "fences" or "fans" i n k i l l e d  continuous sheets of MnS  ~  1 7  I t i s reasonably w e l l agreed  Type II MnS  worked  1  i n rimmed or s e m i k i l l e d  found  is  steel "'  inclusions.  Since t h i s  out  phenomenon  1 3  Figure  3 - Standard f r e e energy of formation of some oxides important i n steelmaking.  TEMPERATURE, ' C  0  500  1000  1500  2000  >  Figure  4 - Standard f r e e energy of formation of some s u l p h i d e s important i n steelmaking.  14  Figure  5 - Schematic r e p r e s e n t a t i o n of m o d i f i c a t i o n of i n c l u s i o n s with Ca-treatment 1  has  not  been  observed  the mechanism of formation i s probably  di f f e r e n t . Salter  and  investigated  Pickering  the  2 0  and  of  these  seen at  Calcium  temperatures  oxide phase i s between 36 and  have  2 1  solution the  reacts  composition  formed w i l l  68 weight %.  2 0  liquid  However, even  content can produce round hard i n c l u s i o n s ,  the i n c l u s i o n .  be  As  i f the c a l c i u m oxide content of the  content of aluminium f r e q u e n t l y decreases of  Farell  being dependent on s e v e r a l elements i n the s t e e l .  steelmaking  CaO  in  present to form calcium aluminates,  i n F i g u r e 6, the c a l c i u m aluminates  total  and  t r a n s f o r m a t i o n of indigenous i n c l u s i o n s a f t e r  a d d i t i o n of calcium to the s t e e l . with alumina  Hilty  H i l t y and F a r e l l  2 1  toward  the  lower  s i n c e the periphery  and Haida e t . a l .  2 2  have  15  suggested steel  that the composition  composition  composition content  of aluminates  according  to  is related  F i g u r e 7.  The  to  aluminate  would then be dependent on only sulphur and  at  constant  aluminium  content.  However,  calcium s i n c e the  content of oxygen a l s o changes i n the same d i r e c t i o n as in these i n v e s t i g a t i o n s , more  complex.  i t i s probable  Faulring  and  will  form.  sulphur  that the r e l a t i o n s h i p i s  Ramalingam  have  23  i n c l u s i o n p r e c i p i t a t i o n diagram as an a i d i n aluminates  the  Unfortunately,  proposed  determining  due  to  the  an  which  lack  of  thermodynamic data f o r c a l c i u m i n s t e e l s o l u t i o n s the diagram i s given i n  terms  applied appears  Henrian  thermodynamic to be  Calcium around  of  activities.  data  for  sulphide i s  usually  aluminates  solubility  of MnS  of  solubility  of about  is  calcium aluminate  system  about  found  with  As can be seen  2  type II  their  2  calcium  calcium  addition,  erroneous ".  higher than CA .  in  the  In  as  calcium  a  peripheral  content  equal to or  i n F i g u r e 8 the CaS  10 mole %,  14 mole- % CaS.  Any  and  MnS  rim  has a s o l i d  has  a  solid  "high content MnS"  found  t r e a t e d s t e e l s are of type I I I , and the d e l e t e r i o u s entirely  eliminated.  In  addition  to  the  more  advantageous shape, the s u l p h i d e s f o r c a l c i u m - t r e a t e d s t e e l s are also  harder  Figure 9 . 2 5  than  those  in  untreated  steels,  as  seen  However, the t r a n s f o r m a t i o n of s u l p h i d e s may  only advantageous.  I t has been suggested  not  in be  that c a l c i u m s u l p h i d e s  are d e t r i m e n t a l to the c o r r o s i o n r e s i s t a n c e of s t e e l ' 2 6  2 7  .  16 2100  1  1  •  —  I  1  — i  1  i  2000 To CaO MP  1900  / Liquid  \  1800 TEMP °C 1700  /Liq. .  Liquid  —\  / Liquid  \—|  1  2  10  20  CA -  2  6  •  CA Al 0 90 100  3  2  Figure  3  3  1  CQO  0  Al,0  CaO UqUid + C A Liquid C A + CA 1 • CA CA CAj 30 40 50 60 70 80 Weight % Al 0  V  1300  > CA  C  CA + CA  1500 1400  -  /XA,  CaO + Liquid  1600  -  6  6  2  3  3  6 - The pseudo b i n a r y calcium oxide - aluminium oxide phase diagram"".  12Ca0 7AI 0 2  CaO Al 0 2  3  3  Ca0-2AI 0 2  Ca06Al 0 2  0  10  20  30  40  50  j  60  i  70  i  80  3  3  i_  90  CALCIUM content of steel, ppm.  Figure 7 - Composition of c a l c i u m aluminates as a f u n c t i o n of s t e e l c a l c i u m content. H i l t y and F a r e l l , Haida e t . a l . . 2 1  2 2  1 7  1 1 r-  T  \  2400 K 2200 2000  LIQUID  1800 TEMP o 1600  161C  C  1400  (Co, M n ) S  0  20  40  60  80  100  CaS  MnS Mole  Figure  % MnS  8 - The pseudo binary c a l c i u m s u l p h i d e — manganese sulphide phase d i a g r a m . 25  I  I  '  1  '  I  I  1  '  ^"^^-^g^oCoS  200 HARDNESS  kg./mm.  2  - \  100  >w  — \  ^^^0  X.  m  / CaSo  ^ • ^ ^ C a S ^ ^ ^ 2  %CQS_  ^ ^ - ^ . . P u r e MnS i  0 0  200  .  I  400  .  I  600  TEMPERATURE ,  Figure  .  I  .  800 °C  9 -Diamond pyramid hardness versus temperature f o r some(Mn,Ca)S s o l i d s o l u t i o n s . 2 5  18  2.4 Thermodynamic P r o p e r t i e s 2.4.1  Calcium The  Metal  thermodynamic  established  and  data  for  pure  have been compiled Vapour pressure data  Schurmann  a  at  30  later  date.  are  by K u b a s h e w s k i  JANAF t a b l e s . 2 9  calcium  have  been  28  well  and i n the  evaluated  by  Calcium has a melting p o i n t of  839°C and a b o i l i n g p o i n t of 1 4 9 4 ° C .  The vapour  given by the f o l l o w i n g equation between  1200 and 1700°C °:  29  pressure  is  3  18482 l n p°= 10.48 -  (p i n atm, T i n K)  ... (2.1)  T  2.4.2  Calcium Numerous  thermodynamic addition, exist  3 8  In S t e e l attempts  have  been  made  to  establish  p r o p e r t i e s of c a l c i u m i n i r o n s o l u t i o n s  several  compilations  or  comparisons  3 1  "  of  3 7  the .  In data  -" . 1  The r e a c t i o n s of i n t e r e s t a r e :  CaO(s) = [Ca] + [0]  ... (2.2)  CaS(s) = [Ca] + [S]  ... (2.3)  These  reactions  reactions:  can  be  obtained  by  combining the f o l l o w i n g  19  CaO(s) = C a ( l ) +  1/20  2  (2.4)  CaS(s) = C a ( l ) +  1/2S  2  (2.5)  l / 2 0 ( g ) = [0]  (2.6)  l / 2 S ( g ) = [S]  (2.7)  C a ( l ) = [Ca]  (2.8)  2  2  The  equilibrium  reasonably  constants  well-known 2  s o l u b i l i t y of calcium pure  calcium.  8  2 9  i  3 9  .  reactions  Sponseller  in l i q u i d  Based  for  on  steel  The  data  of  this  maximum  a  solution. sulphur  yield  calcium  than  the  value  given  of be  a Raultian  in  3  pure  iron  the oxygen and  Thus, part of the calcium  bound as sulphide or oxide.  would mean that the a c t u a l s o l u b i l i t y lower  also  for  in the "pure" i r o n s o l u t i o n .  liquid  solubility  However, S p o n s e l l e r ' d i d not c o n s i d e r  " s o l u b l e " in i r o n was probably  the  f o r r e a c t i o n 2.8 can  Sponseller  a c t i v i t y c o e f f i c i e n t , ii£ , of 2270  measured  3 1  in e q u i l i b r i u m with  0.032 weight %, an e q u i l i b r i u m constant calculated.  2.4 to 2.7 are  of  calcium  by S p o n s e l l e r .  in  This  iron  is  However, as other  data are l a c k i n g i t w i l l be a p p l i e d t o c a l c u l a t e the e q u i l i b r i u m constant  f o r r e a c t i o n s 2.2 and 2.3.  K.  = 5.3 x 10 1 1  K.  = 1.6 x 10"  2  2  2  3  At 1600°C t h i s  ...  9  ...  Corresponding i n t e r a c t i o n c o e f f i c i e n t s have been the  calcium  yields:  oxygen  interaction coefficient  interaction for  calcium  assuming is  zero,  (2.9) (2.10)  suggested that  the  eo = -535 Q  for selfand  20  e ° = -1330. c  Q  A  different  workers " . 3 3  approach  has  been  taken  by  They assume that a l l n o n - m e t a l l i c  3 7  s e v e r a l other i n c l u s i o n s have  been removed from a s t e e l melt i n contact with CaO a  certain  calcium  time.  in the quenched  solution.  This  constant",  2  K* .3 2  2.4.3  =  4.5  =  3.2  2  One  steel  assumed  equal  yields  "an  apparent  x  B  x  to  Ca  10" ; 7  the  equilibrium interaction  Gustafsson  3fl  .  (2.11)  ef = -110  ...  (2.12)  importance geology  =  of  the  c a l c i a alumina system i n  and m e t a l l u r g y ,  s e v e r a l authors  thermodynamic p r o p e r t i e s " " . 2  For  2580°C  and  5 1  not  recent l i t e r a t u r e v a l u e s ' 2 9  melting  2950°C. the  melting  temperature  Thus, point  have  In s p i t e of  for the system are s t i l l  instance,  c a l c u l a t i o n s connected to errors.  in  - ...  0  the seemingly simple property of between  that  Aluminates  its  established.  to  of  -150  e  10" ;  i s given by  after  content  with  3  f a c t , the thermodynamic data  vary  analysed  is  such set of values  cement technology, discussed  chemically  approach  2  Calcium Due  the  K* .2 or K* . , which i s c o o r d i n a t e d  parameters.  K* .2  Thus,  or CaS  all  this well  5 2  of  for CaO,  thermodynamic  could  introduce  21  An  effort  has  been  made  a v a i l a b l e thermodynamic data. b i n a r y CaO  -  Nurse e t . a l . ,  water or halogens""' "  Eliezer e t . a l .  5 0  Redlish-Kister  5 3  the most recent  The phase diagram  1 2  A  and  9  7  f o r the pseudo-  i s not  coefficients  i n t e g r a l enthalpy of mixing  determined  i s s t a b l e only i n the  for  by  presence  i n c l u d e d i n t h i s diagram.  have e v a l u a t e d l i t e r a t u r e  l i q u i d c a l c i u m aluminates and  given  determine  as given i n F i g u r e 6 was  The phase C  u  of  system  AI3O3  to  data  the  and  suggested  enthalpy of mixing f o r  f o r the a c t i v i t y c o e f f i c i e n t .  f o r the l i q u i d CaO-AlOLs  system  The is  by  H = X X [-123.16 + 41.79(X,- X ) 1  2  2  + 30.80(X 1  X )  2  2  - 27 . 06(X,-X ) ] ,  ...  3  2  where X,  (or  coefficient  X )  is  for  the  2  X  either same  or  C q Q  system  x  at  AIO  15  *  T  ^  (2.13)  activity  e  1000K, with l i q u i d  pure  oxides as standard s t a t e i s given by  loqf,=  X [-5.885 + 1 . 1 45 ( 3X, - X ) +.723(X,+ X ) ( 5 X - X ) 2  2  -.610(X,- X ) ( 7 X , - X ) 2  2  This  activity  standard  2  coefficient,  state  will  c a l c i u m aluminates The most system  are  be  1  +.493(X,- X ) ( 9 X , - X ) ]  ...  (2.14)  temperature  and  3  2  corrected  used  in  the  2  for  2  calculations  involving  together with f u s i o n data from JANAF . 2 9  recently those  a c t i v i t i e s of CaO  2  published of  and A l 0 2  Lourtau 3  experimental et.al." . 9  data They  of  this  determined  i n order to o b t a i n the f r e e e n e r g i e s  22  of formation of  the  inter-oxide  compounds,  and  presented  a  r e l a t i v e l y complete set of data f o r the system. 2.4.4 Calcium The  Sulphide  thermodynamic data f o r CaS have been taken  from JANAF .  S i m i l a r l y , as  29  melting  of  CaS  may  not  with be  CaO,  data  exclusively  related  to  the  r e l i a b l e due to the high m e l t i n g  point. 2.5 Evaporation Rate In a good vacuum (p < 10" the  surface  of  a  metal  atm) the e v a p o r a t i o n  3  melt  is  described  rate  from  by the Langmuir  equat ion " : 54  58  m = 44.33St /M/T  This  YxpV '  ... (2.15)  equation shows that the evaporation r a t e i s independent  t o t a l pressure exposure and If  but  dependent  on  evaporation  melting  time  almost  a l l calcium  is  bound  as e i t h e r CaS or C A , x  A sample c a l c u l a t i o n conditions,  shows  (A = 3700 cm , 2  that  that the Henrian limiting  activity  for  T = 1600°C)  step  will  i n the s t e e l not  s o l u t i o n , but rather the r e a c t i o n  be  realistic an  amount  in  assuming the  evaporation of c a l c i u m  from  the  0.1 ppm.  VAR  Thus,  of  is  y  from a very d i l u t e  excess of 1 ppm calcium would h y p o t h e t i c a l l y evaporate,  rate  of  temperature.  e v a p o r a t i o n of c a l c i u m i n s o l u t i o n w i l l occur solution.  area,  of  inclusion  compounds  23  p r e s e n t on the s u r f a c e g i v i n g r i s e t o the c a l c i u m i n s o l u t i o n .  24  III.  EXPERIMENTAL  PROCEDURES  3.1 Samples Two  types  corresponding  of  samples  were  e l e c t r o d e and VAR  d i f f e r e n t companies.  To  investigated.  Samples from  i n g o t s were o b t a i n e d from  supply  additional  data,  three  laboratory  samples produced with the a i d of the i n d u c t i o n and e l e c t r o n beam furnaces at UBC were 3.1.1  prepared.  I n d u s t r i a l Samples The  i n d u s t r i a l l y produced s t e e l s were of the h i g h - s t r e n g t h  l o w - a l l o y type.  In a l l c a s e s , the e l e c t r o d e s t e e l s  treated  calcium,  with  either  by  " F e r r o c a l c i u m " or by wire a d d i t i o n . Remelted under approximately  direct  were  ladle  addition  of  The s t e e l s were Va,cuum  Arc  the c o n d i t i o n s given i n Table 1.  3.1.2 Laboratory Samples The  l a b o r a t o r y e l e c t r o d e s were prepared  i n d u c t i o n furn-ace. of i m p u r i t i e s .  kilogram  Magnesia c r u c i b l e s were used t o a v o i d p i c k u p  The i n i t i a l  Table  in a five  charges  of "Armco i r o n " were  melted  1 - VAR m e l t i n g c o n d i t i o n s  E l e c t r o d e diameter: 470 mm Ingot diameter: 500 mm Melting rate: 300 kg/hr Pool temperature: 1500 - 1680°C Operating p r e s s u r e :  10"  3  - 5X10"  3  torr  Note: P a r a b o l i c distribution.  25  under  a  shield  of  argon.  p r e l i m i n a r y d e o x i d a t i o n was graphite  rods.  When the e n t i r e charge was performed by s t i r r i n g  Appropriate  amounts  of  the melt  was  i n t o the melt. crucible.  In  added by plunging p e l l e t s wrapped i n i r o n  Unfortunately,  inclusions. some  did  not  melts  poured  contain  cases,  into  the  T h i s c o u l d have been due  from the bath,  Finally  The melts were then allowed to s o l i d i f y  solidification  with  the a l l o y a d d i t i o n s ,  ferromanganese, i r o n sulphide and aluminium were added. c a l c i u m metal  molten,  a  in  foil the  mould before  desirable  types  of  to e x c e s s i v e r e o x i d a t i o n .  p i n samples of a diameter  of 4.2  i n order to study the i n c l u s i o n s  mm  in  were taken the  liquid  melt. The  melting  procedure  produced  a  cylindrical  Samples- for a n a l y s i s were cut from the middle such  of  the  ingot. ingot  in  a manner as to a v o i d the areas a s s o c i a t e d with the o u t s i d e  s u r f a c e and several  solidification  electrodes  shrinkage  (see  F i g u r e 10).  One  or  f o r subsequent E l e c t r o n Beam r e m e l t i n g were  cut along the c y l i n d e r . The  e l e c t r o d e s were remelted  i n a 15 kW  beam furnace u t i l i z i n g a gun manufactured Ardenne Figure An  Research 11.  Institute .  the  furnace  Manfred is  shown  The c o n d i t i o n s for r e m e l t i n g are given i n  Table  1 0  The  by  laboratory electron von in 2.  arrangement of m i r r o r s made i t p o s s i b l e to watch the melt i n  progress.  26  Figure  11 - The E l e c t r o n Beam furnace at UBC.  27  Table  2 - EB remelting  Electrode crossection: Melting rate: Melt s i z e : Operating p r e s s u r e :  conditions  2.2 - 4 cm 0 . 7 - 1 kg/hr 200 g 10-* t o r r 2  3.2 A n a l y s i s 3.2.1 M e t a l l o g r a p h i c Sections and  of both e l e c t r o d e and ingot m a t e r i a l s were  polished.  contact  Examination  To  prevent o x i d a t i o n of the c a l c i u m  with water was avoided  the samples were s t o r e d General  some  of  stage  and  1 5  examination  i n s i t u was obtained  - EDX a n a l y s i s . for  the p r e p a r a t i o n  was done with  Q u a l i t a t i v e and s e m i q u a n t i t a t i v e  inclusions  sulphides,  in a d e s s i c a t o r .  metallographic  microscopy.  during  ground  Quantitative  optical  analysis  of  the  by Scanning E l e c t r o n Microscopy  inclusion analysis  was  performed  the samples by e l e c t r o n microprobe a n a l y s i s .  The  standards f o r microprobe a n a y l s i s were: Pure Mn, pure Fe, A l 0 , 2  CaC0  3  and ZnS.  IV program. during  The raw i n t e n s i t i e s were c o r r e c t e d using a Magic  The phases f r e q u e n t l y  microprobe  interfere  a n a l y s i s , as the c a l c i u m  as a p e r i p h e r a l rim around schematically  described  the in  Figure  analyse  Unfortunately,  with  12. S,  The and  each  sulphide  aluminates.  overcome i f 5 elements (Fe, Mn, Ca, simultaneously.  3  This  i s present problem  problem Al)  other  are  can  is be  analysed  the microprobe at UBC can only  two elements simultaneously.  Therefore,  most  of  the  microprobe a n a l y s i s was done on e l e c t r o d e m a t e r i a l s where l a r g e r  28  POLISHED  ELECTRON  F i g u r e 12 - Schematic d e s c r i p t i o n of the problems with microprobe a n a l y s i s . Note that a l l three i n c l u s i o n s g i v e the same appearance from the s u r f a c e . a) Ca, A l , S, Fe, (and sometimes Mn) must be analysed simultaneous to determine the C/A r a t i o . b) Ca, A l , S, (and sometimes Mn) must be a n a l y s e d . c) Only i n t h i s case can an a c c u r a t e C/A r a t i o be o b t a i n e d by a n a l y s i n g only two elements. i n c l u s i o n s c o u l d be 3.2.2  Bulk S t e e l Bulk  found.  Composition  analysis  of  spectrographic a n a l y s i s . the  vacuum  combustion The  fusion  most  elements  was  The oxygen content was  method  and  the  sulphur  contents  spectrophotometry  using  were a  determined modified  d e s c r i b e d by H i l t y and F a r e l l  2 1  by  determined  by  content  iodometric method a c c o r d i n g t o standard  calcium  obtained  by  the  procedures.  with atomic a b s o r p t i o n  version  of  the  , as d e s c r i b e d i n Appendix  method B.  29  3.2.3  Inclusion Extraction In order to confirm the e l e c t r o n microprobe a n a y l s i s and to  determine  the  inclusion  composition  f o r the  m a t e r i a l s with  i n c l u s i o n s too small for microprobe a n a l y s i s , chemical e x t r a c t i o n was performed.  Methanol bromine e x t r a c t i o n under dry  c o n d i t i o n s was a p p l i e d according t o the technique Reyes-Carmona .  By  59  inclusion  subjecting  artificial  described  calcium  by  aluminates  and calcium s u l p h i d e to the e x t r a c t i o n , i t was determined that a mixture  of C A and CA or pure CA do  does d i s s o l v e . to  determine  or oxide  the  quantity  i n the s o l i d  The  collected  solution atomic  by  the  of  calcium  c a l c i u m aluminate  inclusions  were  analysis.  sulphide. calcium  assuming  contamination prevented very  60  analysing  either  of  that  the  to  aqueous  f o r subsequent  calcium  a l l oxygen  i n the  aluminates was bound as  i n the s t e e l . the calcium i n s o l u t i o n  T h i s calcium r e p r e s e n t s the  the  calcium  apparatus.  Another  of the e x t r a c t e d p r e c i p i t a t e s by  bound  from as  due to p i c k up of problem  was the  carbides.  weighing of the oxide phase and made x-ray  difficult.  sulphide  f o r Ca  U n f o r t u n a t e l y , t h i s f a i l e d probably from  made i t p o s s i b l e  transferred method  By  An attempt was made to analyse the e x t r a c t i o n .  CaS  steel.  i n c l u s i o n s , the average composition determined  whereas  bound as oxide and as  i s bound as  lithium-metaborate  absorption  be  dissolve  Thus, t h i s s e p a r a t i o n technique  s u l p h i d e assuming that a l l calcium  could  not  3  This  diffraction  30  IV. 4.1  Thermodynamic Calcium  phase. gas at  be present  in four phases d u r i n g  s o l i d s u l p h i d e , l i q u i d or  Consider  solid  remelting,  oxide,  and  the e q u i l i b r i u m between d i s s o l v e d c a l c i u m  gas and  1600°C:  [Ca] = Ca(g)  As  DISCUSSION  Considerations  could  l i q u i d metal,  RESULTS AND  the  K=57.5 (30,31)*  total  r e m e l t i n g , and higher,  it  according Therefore,  pressure the  follows  to  partial that  reaction  calcium  does  not exceed  pressure the  4.1,  of  be  atm  3  calcium  activity will  10"  ...  (4.1)  during  can  not  VAR be  of c a l c i u m i n the melt lower  than  i n the metal phase w i l l not be  0.2  ppm.  considered.  However, i t i s p o s s i b l e that d i s s o l v e d c a l c i u m takes p a r t i n the r e a c t i o n s as an for  reaction  intermediate 4.1  species.  i s probably  equilibrium  review.  a n t i c i p a t e d lower s o l u b i l i t y of  in  would y i e l d an even higher K., .  would be v a l i d a l s o i n that  constant  i n a c c u r a t e as p o i n t e d out  literature steel  The  The  u  i n the calcium  Thus, the assumption  case.  * The standard s t a t e f o r s u l p h i d e s and oxides i s pure s o l i d compounds. The standard s t a t e f o r elements d i s s o l v e d i n iron solution i s Henrian i n f i n i t e l y d i l u t e s o l u t i o n . References are given i n p a r e n t h e s i s where new e q u i l i b r i u m data have been applied.  31  Calcium sulphide during  vacuum  could take part  + [S](in C A ) x  CaS(s) = CaS(g) + 1/2S  CaS(s) = Ca(g)  + [S]  CaS(s) + 1/3A1 0 2  3  =  . . . (4.2)  y  •  CaS(s) = Ca(g)  2  K= 6.4  X  1 0- (29)  . . . (4.3)  K= 2.2  X  10" ( 2 9 , 3 0 )  ... (4. 4)  K= 9.3  X  10- (39)  ... (4. 5)  +  2/3[Al] + [S]  CaO(l, in C A ) x  y  K= 1 .3 X  has been shown*  a C A x  average  place  equilibrium  not  be  constants  standard  reactions the  of  lower s o l u b i l i t y i t will  under  50 weight %  4.5  species.  conjunction  10"  ... (4. 6)  3  is  of sulphur i n  1.4 weight %.  The  side.  of  show  Since  these  even i f r e a c t i o n 4.2 takes  quantitative that  aluminates  4.5  However,  importance.  i s most l i k e l y the  The  to occur  probability  that  4.6 w i l l occur depends on the a c t i v i t i e s of  These  with other  Possible  8  CaO  of sulphur,  conditions. and  1o  the aluminate i n c l u s i o n s i n a s t e e l i s  to be on the alumina r i c h a  9  that the maxiumum s o l u b i t i l i y  composition  likely have  7  melt c o n t a i n i n g  y  reactions  remelting:  CaS(s) = Ca(g)  It  i n the f o l l o w i n g  reactions possible  will  be  discussed  later  in  reactions.  r e a c t i o n s that the oxide phase c o u l d  take part i n  are:  CaO(l,  i n C A ) = CaO(g) x  y  K= 6.4 x 10" (24) 11  CaO(l,  i n C A ) + [C] = Ca(g) x  y  + CO(g)  ...  (4.7)  32  K= 1.5 x 10"  5  ...  (4.8)  ...  (4.9)  1/3A1 0 (1, i n C A ) + [C] = 2/3[Al] + CO(g) 2  3  x  y  R= 2.1 x 10"'  Of  these r e a c t i o n s , 4.8 and 4.9 appear most l i k e l y Further  4.6,  to occur.  i n v e s t i g a t i o n of the f e a s i b i l i t y of r e a c t i o n s 4.5,  4.8 and 4.9 i n an i n d u s t r i a l  s t e e l r e q u i r e s a knowledge  of  the thermodynamic p r o p e r t i e s of the elements i n s t e e l s o l u t i o n . However,  as  mentioned  thermodynamic  data  in  the  f o r calcium  in  parameters  established.  Because of t h i s , a h y p o t h e t i c a l  aluminum  discussed.  and  composition  has  data '  9  29  ' ' " - '  Table 3.  sulphur  in  solution  elements  the  review,  are  steel  the  and i t s not with  well only  s t e e l s o l u t i o n w i l l be  The Henrian a c t i v i t i e s of the d i s s o l v e d elements and  the a c t i v i t i e s of CaO  28  other  steel  interaction  carbon,  with  literature  3 9  5 1  The  and  Al 0 2  in  3  been determined using 5 3  .  The h y p o t h e t i c a l  activities  in  C A x  y  f o r the  the mentioned steel  interesting reactions:  R4.5  = 2.7 x  10-  6  R«.6  = 4.9 x  10"  5  R«.8  = 2.5 x  10"  5  R4.9  = 4.6 x  10-"  As  can be seen, there  (K  the h y p o t h e t i c a l  in  s t e e l y i e l d the ("=R") f o r  = 9.3 x 1 0 - ) 8  ft5  (K, (K  literature  i s described  f o l l o w i n g r a t i o s of r e a c t i o n products over r e a c t a n t s the  "example"  s  =  1.3  x  10" )  a 8  =  1.5  x  10- )  =  2.1  x  10" )  (K„  9  3  5  1  i s a thermodynamic d r i v i n g f o r c e f o r both  33 Table  3 - D e s c r i p t i o n of the h y p o t h e t i c a l ASSUMED PROPERTY  METAL PHASE: Sulphur Aluminium Carbon  c c c  INCLUSIONS: CaS(s) C A X  X  =.0025wt%* =.025 wt%* =.30 wt%*  s A| c  CQS  C  y  VALUE USED IN CALCULATIONS  =  1  „'  a  CcS  a  =  =  C a 0  I  ^  0.12**  Al 0 = 2  P = 10p = 10-  39 39 39  s  A|  a  GAS PHASE: Calc ium CO  REFERENCES  h =.0027 h =.027 hQ =.33  = 40 wt%  C q 0  steel  °'  3  2 1  29, 28,  49, 50 49, 50  **  3  r  C o  3  P n " * S, A l and C are the only elements assumed present *co= " ** a = .13,.11 at 1550°C and 1650°C and a = .23,.l9. =  CO  1 0  3  C  1 0  c  in solution.  3  A  r e a c t i o n s 4.6 and 4.9 to occur. The average  temperature of 1600°C has been adopted as a temperature  the pool  during  temperature  VAR  does  4.6, 4.8, and 4.9 results  of  i n the l i q u i d melting.  not were  of  f i l m on the e l e c t r o d e and i n  To  ensure  reaction  evaluated  at  1550  However,  r e a c t i o n s 4.6 and 4.9 are s t i l l  higher  and  in Figure  i n temperature w i l l 4.8.  that  reactions  These a r e :  are  most  shift  the  likely  1650°C. 13.  increase driving  in  The  The f i g u r e  the  driving  forces  for  at a l l temperatures.  From t h i s simple thermodynamic d i s c u s s i o n two  a  the r e l a t i o n s h i p , r e a c t i o n s 4.5,  t h i s e v a l u a t i o n are given  shows that an i n c r e a s e force  change  reasonable  i t appears  to occur d u r i n g VAR  that  melting.  34 TEMP., °C 1600  1550  Figure  1650  13 - E v a l u a t i o n of the thermodynamic d r i v i n g force,  CaS(s) + 1/3A1 0 (1, i n C A ) = CaO(l, 2  3  x  y  i n C A ) + [S] + 2/3[Al] x  y  1/3A1 0 (1, i n C A ) + [C] = 2/3[Al] + CO(g) 2  3  x  y  4.2 E l e c t r o n Beam Remelting The  e l e c t r o n beam remelting  q u a l i t a t i v e manner the e f f e c t of  experiments served vacuum  remelting  to show i n a on  calcium  containing inclusions. During  remelting,  i n c l u s i o n s c o u l d be observed both on the  e l e c t r o d e t i p and on the pool s u r f a c e .  These i n c l u s i o n s s t a r t e d  c o a l e s c i n g on the e l e c t r o d e and formed "beads" of i n c l u s i o n s the  pool  surface.  The  beads  had a tendency to f l o a t  on  to the  35  edges of the Figure  i n g o t , where they would f r e e z e to the s o l i d  14 shows an i n c l u s i o n bead which was  surface  of  a  frozen  c a l c i u m aluminate together. was  and  However,  .ingot.  the  phase  calcium  than  f i g u r e shows, both  Microprobe and  in  the  the  coalesced  calcium  s t e e l , as can be seen i n F i g u r e  the out  SEM-EDX a n a l y s i s show beads  aluminates  15.  contains  that  p o s s i b l y take p l a c e during r e m e l t i n g .  give enrichment of c a l c i u m oxide  more  i n the e l e c t r o d e  These o b s e r v a t i o n s  with the thermodynamic d i s c u s s i o n i n d i c a t e  explains  the  the amount of c a l c i u m s u l p h i d e in the bead  that the oxide  and/or 4.9  from  the c a l c i u m s u l p h i d e i n c l u s i o n s f l o a t  smaller than expected.  oxide  As  collected  shell.  together  reactions  4.6  Both r e a c t i o n s  i n the oxide phase but only  4.6  the small amounts of c a l c i u m s u l p h i d e which remains i n  the c o a l e s c e d beads. Metallographic analysis that  example of c o a l e s c e d 4 . 3 I n d u s t r i a l VAR The  is  content  on  an  electrode  electrodes Figure  tip  confirm 16 shows  containing  an  inclusions. Samples bulk a n a l y s i s of the  ingot samples are given  interesting  to  note  that  i n Table  4.  industrial  In t h i s t a b l e  r e g a r d l e s s of the e l e c t r o d e  of c a l c i u m , the ingot w i l l c o n t a i n only between 5 and  Another  sulphur  film  r e s u l t s of the chemical  e l e c t r o d e and  ppm.  sectioned  the i n c l u s i o n s c o a l e s c e during r e m e l t i n g .  the e a r l i e r molten  it  of  interesting  observation  i s g e n e r a l l y l e s s than  10  ppm.  is  that  the  loss  10 of  36  F i g u r e 14 - "Bead" o f c o a l e s c e d i n c l u s i o n s c o l l e c t e d f r o m s u r f a c e of EB-melted i n g o t . The b l a c k p a t c h e s a r e CaS a n d t h e b u l k phase i s C A . (The bead h a s been g l u e d t o t h e s u b s t r a t e . ) SEM image x 2 8 . x  y  INCLUSION  •A.  BEAD Mg  Co  Ca  ENERGY  F i g u r e 15 - X - r a y s p e c t r u m s s h o w i n g t h e r e l a t i v e c o m p o s i t i o n o f an i n c l u s i o n i n a n e l e c t r o d e s t e e l a n d c o r r e s p o n d i n g i n c l u s i o n "bead".  37  F i g u r e 16 - Coalesced i n c l u s i o n s on an e l e c t r o d e t i p . L i g h t microscope and SEM X-ray images.  38  Table 4 - Summary of a n a l y s i s . Vx marked s a m p l e s denotes e l e c t r o d e s t e e l s , and VxR marked samples a r e corresponding • remelted ingots.  Total content s t e e l (wt%)  Steel Ca  in  Content aluminate  Al  0  S  in (wt%)  Ca  Ca/Al  Al  V1 V1R  .0029 .0006  .030 .017  .0066 .0022  .0050 .001 5  .001 4 .0003  .013 .0024  .16 .08  V2 V2R  .0063 .0005  .030 .024  .0068 .001 4  .006 .0052  .0025 .0002  .008 .0042  .26 .10  V3 V3R  .0060 .0007  .026 .022  .0060 .0021  .0070 .0060  .0018 .0004  .011 .010  .20 . 1 3  V4 V4R  .0062 .0006  .053 .034  .0069 .0014  .0037 .0031  .0035 .0005  .027 .0064  .38 .25  V5 V5R  .0030 .0008  .023 .021  .0054 .001 6  .001 5 .0012  .0015 .0001  _  -  .18 .05  V6 V6R  .0020 .0002  .024 • .024  .0032 .0025  .0023 .0021  .001 1 .0003  .0035 .011  .26 .02  *Based  on  Table VAR  5  either  The  was  or  phase,  the  and  oxygen  agrees  hand,  the  the  was  distribution  electrode  of  of  the well  the  that  interest  oxygen  a l l  is  calcium and  rejection  that  to  a  on  the  loss  composition  of  the  calcium  ingot.  between As  the  loss  aluminium  can  actual  of  sulphide  be  seen,  oxygen  aluminium  loss.  This  is  during  aluminium,  electrode is  of  based  calcium  analysed  predicted  in  elements of  assuming  further  with  the  loss  inclusions  known  aluminates.  of  predicted  sulphide  mechanism  tiie  loss  calculated  prediction  oxide  for  the  The  oxide  removal  balance  shows  melting.  sulphur  the  Ca/O  of  and  the  bound the  free  as  sole  surface.  calcium  in  the  aluminates  and  oxide  the  in  predicted  loss.  On  erratic  as  is  and  probably  loss  the  other  compared due  of  to to  39 Table  5 - R e s u l t s of mass  Atom% l o s t during  Steels  Ca  Al  balances  remelting  0  S  Al  VI : In i n c l . .0016 Total .0033  .022 .027  .013  .0062  V2: In i n c l . .0032 Total .0081  .007 .012  .019  .0019  V3:  In i n c l . .0021 .0074 Total  .002 .008  .014  .0020  V4: In i n c l . .0034 Total .0073  .043 .040  .019  .001 1  V5: In i n c l . .0020 Total .0031  .002  .013  .0003  V6: In i n c l . .0011 Total .0025  .0  .002  .0003  *Assumption: The i n c l u s i o n s f l o a t out. based on c a l c i u m l o s s . interference  from  aluminium  Predicted 0  to  S  .010  .017  .001 7  .012  .022  .0049  .010  .018  .0053  .009  .017  .0039  .011  .018  .001 1  .004  .007  .0006  The mass balance i s  nitrides.  Firstly,  the aluminium  n i t r i d e s would f o l l o w a s i m i l a r removal p a t t e r n d u r i n g as the oxides, and secondly  loss*  remelting  the aluminium n i t r i d e s are r e s i s t a n t  bromine-methanol d i s s o l u t i o n .  However,  6 1  i t appears  that  r e j e c t i o n to a f r e e s u r f a c e i s the major mechanism of removal of calcium  aluminates.  The times  p r e d i c t e d l o s s of sulphur  higher  than  the  actual  i s , except loss.  mechanism takes p a r t i n the removal while  the  sulphur  of  i n one case,  Evidently, calcium  remains i n the s t e e l .  from  three  some other sulphide  C o n s i d e r a t i o n of the  thermodynamic c a l c u l a t i o n s and the EB experiments suggests  that  the l i k e l y a d d i t i o n a l removal mechanism i s that of r e a c t i o n 4.6:  40  CaS(s) + 1/3A1 0 (1, i n C A ) = CaO(l, 2  This  agrees  sulphur  3  x  well  with  y  i n C A ) + [S] + 2/3[AL] x  y  the f a c t that calcium  i s removed while  remains i n the s t e e l .  To  summarize,  rejection  the  calcium  to a f r e e s u r f a c e .  i s a l s o removed by r e j e c t i o n .  aluminates  are  removed  One t h i r d of the calcium  by  sulphide  The remainder r e a c t s a c c o r d i n g to  e q u i l i b r i u m 4.6 t o form c a l c i u m oxide  and  dissolved  sulphur.  Subsequently, the formed oxide w i l l be removed with the o r i g i n a l oxide  phase  sulphide,  by iron-  solidification Reaction oxide  r e j e c t i o n , and the sulphur w i l l sulphide  or  depending on the s t e e l  during  composition.  However, i t does not account f o r  the l o s s of c a l c i u m while sulphur  4.9  sulphide  4.9 could c o n t r i b u t e to t h e i n c r e a s e of CaO i n the  phase d u r i n g r e m e l t i n g .  fact,  chromium  form manganese  in addition  remains i n  to l i t e r a t u r e d a t a , 9  the  suggests  i s i n h i b i t e d or slowed down, while r e c t i o n 4.6  steel.  This  that r e a c t i o n occurs  more  readily. 4•4 General During  Observations the course  R e l a t e d To Calcium  Treated S t e e l s  of t h i s work some o b s e r v a t i o n s were made  which are not d i r e c t l y connected  to  calcium  These o b s e r v a t i o n s w i l l now be  in  discussed.  steel  in general.  vacuum  remelting  but to  41  4.4.1  Calcium Aluminate  Composition  As d i s c u s s e d in the l i t e r a t u r e has  been  suggested  that  review,  the c a l c i u m aluminate  dependent on calcium and sulphur content at content  according  to  Figure 7.  found that the e l e c t r o d e s t e e l s , 60  —  Figure  7 0 ppm,  1 5 0 ppm content  but only 5 0 ppm  constant  aluminium  However, i n t h i s work i t was with  an  oxygen  content  steels  of  Hilty  and  4 3 ppm  oxygen i t appears  i n f l u e n c e s the composition  of  given i n  and  Farell  sulphur and 3 0 ppm oxygen and f o r the other  sulphur  it  composition i s  sulphur, y i e l d the graph  1 7 . C o n s i d e r i n g that the  c o n t a i n 5 0 ppm  (section 2 . 3 . 1 . )  graph  that the oxygen  of the aluminates more than  INFLUENCE OF Ca IN STEEL ON COMPOSITION OF CALCIUM ALUMINATES  12Ca07AI0 2  CaO Al 0 2  3  3  CaO-2AI0 2  3  Ca0-6AI0 2  0  10  20 30 40 50 60 70 80 CALCIUM CONTENT OF STEEL . ppm.  90  3  100  F i g u r e 17 - Composition of c a l c i u m aluminates as a f u n c t i o n of s t e e l c a l c i u m content. Experimental r e s u l t s , and r e s u l t s from H i l t y & F a r e l l and H a i d a *marked s t e e l s have lower oxygen contents than the other s t e e l s 2 1  2 2  42  the  sulphur  content.  composition content  will  but  relatively  be  also  the  resulting  aluminate  dependent not only on sulphur and c a l c i u m  on  complex  Probably  aluminium  subject  and  oxygen  content.  This  can only be r e s o l v e d a f t e r  further  i n v e s t igat i o n . 4.4.2  I n c l u s i o n s In The L i q u i d During  the  investigation  m e t a l l o g r a p h i c s e c t i o n s taken pure  CaS  Steel it  was  observed  from small l a d l e samples c o n t a i n e d  in rims around the aluminates  and pure MnS  type I I I .  On the other hand, samples from l a r g e i n g o t s r e v e a l e d containing  some  MnS  the s o l i d s o l u t i o n enough  time  to  and pure MnS  type I I I .  (Ca,Mn)S only develops  The presence  MnS'  of pure MnS  i n v e s t i g a t i o n of the i n c l u s i o n s  liquid  steel  has  been  c o n t a i n i n g s t e e l was samples taken samples  is  immediately inclusion pure CaS is  published.  prepared  when  in they  An  F i g u r e 18. are  clearly existed  drawn  that  the  a  i n the  calcium  is  bath.  treated  a  calcium and  pin  i n c l u s i o n from one of the p i n As the p i n samples from  the  bath,  i n the l i q u i d s t e e l .  CaS  given  c o u l d be e x p l a i n e d  Therefore,  although the s t e e l c o n t a i n e d roughly  interesting  is  i n the i n d u c t i o n furnace  from the l i q u i d . shown  in  rims  (see a l s o the phase  i f a l l c a l c i u m r e a c t s with e i t h e r oxygen or sulphur No  CaS  T h i s suggests that  i f the  form d u r i n g s o l i d i f i c a t i o n  diagram, F i g u r e 8).  that  The  solidify  the  20  sulphide i s  1% weight Mn.  present as " i s l a n d s "  aluminate,  and not as a p e r i p h e r a l rim as expected  solidified  steel.  nm  It  i n the  i n a normally  43  F i g u r e 18 - I n c l u s i o n i n p i n s a m p l e t a k e n f r o m t h e l i q u i d steel. L i g h t m i c r o s c o p e a n d SEM X - r a y images.  44  Although  the evidence  i s scanty, a  possible  sequence f o r the s u l p h i d e s can be suggested. calcium  precipitation  In the l i q u i d  s u l p h i d e p r e c i p i t a t e s i n or on the c a l c i u m aluminates.  As s o l i d i f i c a t i o n of the s t e e l proceeds, Mn reach  such  either  form a s o l i d s o l u t i o n with e x i s t i n g  individual  a  l e v e l that MnS  MnS  will  segregate  start precipitating.  type III s u l p h i d e s .  solid  The MnS CaS  or  or  sulphur  w i l l be l e f t to form h i g h content manganese (Mn,Ca)S.  no  total  approximately  content  of  sulphur  This w i l l  + [Mn]  It  appears  h i g h MnS  2.5  h a l f the c a l c i u m i s bound as s u l p h i d e . data,  i n the f o l l o w i n g r e a c t i o n , where K i s c a l c u l a t e d at  CaS  form  in weight percent, s i n c e  The h y p o t h e s i s i s supported by the thermodynamic seen  can  calcium  happen i f the t o t a l s t e e l content of c a l c i u m i s s m a l l e r than the  and  If a l l c a l c i u m i n s o l u t i o n  has a l r e a d y r e a c t e d with e i t h e r oxygen  times  bath  = MnS  + [Ca]  unlikely  K = 5.2  x  as  1600°C:  10" ° 1  that the e q u i l i b r i u m can be approached at  a c t i v i t y , while low MnS  a c t i v i t y and corresponding h i g h  CaS a c t i v i t y c o u l d lead to e q u i l i b r i u m c o n d i t i o n s . In an i n d u s t r i a l s t e e l ,  i t i s t h e r e f o r e not s u r p r i s i n g that  no high content manganese (Mn,Ca)S i n c l u s i o n s can be found.  The  b e n e f i c i a l e f f e c t s of s o l i d s o l u t i o n hardening of MnS  inclusions  (see F i g u r e 9) can  very  thus  not  be  contents of c a l c i u m are p r e s e n t .  expected,  unless  high  45  V.  CONCLUSIONS  The c o n c l u s i o n s of t h i s i n v e s t i g a t i o n a r e :  1) The p r i n c i p a l mechanism of removal of c a l c i u m  aluminates  d u r i n g VAR r e m e l t i n g i s r e j e c t i o n to a f r e e s u r f a c e . aluminates  The  are hence c o l l e c t e d on the p e r i p h e r y of the  ingot.  2) Approximately  one t h i r d of the c a l c i u m s u l p h i d e i s removed  together with the aluminates  by r e j e c t i o n t o a f r e e s u r f a c e .  3) Two t h i r d s of the c a l c i u m s u l p h i d e r e a c t s t o form c a l c i u m oxide a c c o r d i n g t o the the f o l l o w i n g r e a c t i o n :  CaS(s) + 1 / 3 A l 0 ( i n 2  3  C A ) = CaO(in x  y  with the c a l c i u m oxide being oxide phases, and the sulphur s u l p h i d e formers,  C A ) + 2/3[Al] + [ S ] , x  y  r e j e c t e d with the o r i g i n a l r e a c t i n g with a v a i l a b l e  f o r i n s t a n c e Mn, during  ingot  solidification.  4) The content 5-10  of c a l c i u m i n the remelted  ingot w i l l be  ppm r e g a r d l e s s of the e l e c t r o d e c a l c i u m  Therefore,  the c a l c i u m treatment  d e s u l p h u r i z a t i o n than  content.  i s more important f o r  f o r i n c l u s i o n shape c o n t r o l .  46  The  results  of t h i s study are not i n agreement with p r e v i o u s  work which attempts  to e s t a b l i s h  the composition of the  c a l c i u m aluminates as a f u n c t i o n of the s t e e l content of sulphur, aluminium  and c a l c i u m .  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Headridge:  1913, pp  v.  52, 1970, pp.  A n a l y s t , v.  106, F e b  51  APPENDIX A - NOTATION oC =  condensation  Y=  activity  a =  activity  A =  A1 0  c =  concentration  C =  CaO  2  C A = x  coefficient  3  xCaO-yAl 0  y  coefficient  2  3  f =  Henrian a c t i v i t y  h =  Henrian a c t i v i t y  H =  integral  K =  e q u i l i b r i u m constant  m =  evaporated mass  M =  molecular weight  p =  vapour  pressure  p°=  vapour  pressure of pure  S =  e v a p o r a t i o n area  t =  time  T =  temperature  X =  atomic  In chemical  coefficient  enthalpy of mixing  of evaporated s p e c i e s  fraction  reactions:  [ ] =  in metallic  (s) =  solid  (1) =  liquid  (g) =  gaseous  solution  element  52  APPENDIX  B  -  D E T E R M I N A T I O N OF C A L C I U M I N S T E E L ABSORPTION SPECTROPHOTOMETRY  BY  ATOMIC  T h i s m e t h o d was a p p l i e d u s i n g a P e r k i n a n d E l m e r M o d e l 306 Atomic Absorption Spectrophotometer (AAS). The method i s a m o d i f i c a t i o n of t h e p r o c e d u r e d e s c r i b e d by H i l t y and F a r e l l . 2  1  A l l g l a s s w a r e w a s c l e a n e d b y i m m e r s i o n i n 5% H N 0 overnight p r i o r to the f i n a l r i n s e in d e - i o n i z e d H 0. The number of p i e c e s of g l a s s w a r e u s e d was m i n i m i z e d and f i l t r a t i o n procedures e l i m i n a t e d to a v o i d c o n t a m i n a t i o n of the samples. 3  2  0 . 5 0 0 g o f c l e a n d r i l l i n g s f r o m e a c h s t e e l was w e i g h e d and t r a n f e r r e d t o a 50ml v o l u m e t r i c f l a s k . F i v e p o r t i o n s of 0.5 g c a l c i u m f r e e i r o n w i r e w e r e p r e p a r e d a n d t r a n s f e r r e d i n t o 50 m l volumetric flasks. Samples and s t a n d a r d s were d i s s o l v e d with 7 ml c o n c e n t r a t e d HN0 a n d 5 d r o p s c o n c e n t r a t e d HC1 p l u s 1 t o 10 m l H 0 a s n e e d e d t o s p e e d u p t h e d i s s o l u t i o n . I n some c a s e s c a u t i o u s h e a t i n g of t h e f l a s k s was r e q u i r e d t o d i s s o l v e the sample. To b o t h s a m p l e s a n d s t a n d a r d s 5 ml of a l a n t h a n u m chloride solution (29 g L a 0 + 200 ml HC1 d i l u t e d t o 1000 m l ) and 5 ml of a p o t a s s i u m s o l u t i o n (52 g K N 0 + 100 m l H N 0 d i l u t e d t o 1000 m l ) were a d d e d t o c o u n t e r a c t t h e depressing e f f e c t s of aluminum and phosphorus and t o c o u n t e r a c t ionization interference. 3  2  2  3  3  3  O f a s t a n d a r d c a l c i u m s t o c k s o l u t i o n c o n t a i n i n g 10 p p m C a , 0.0, 0.5, 1.0, 3 . 0 , and 5.0 ml were added t o t h e standard solutions. A l l s o u t i o n s were d i l u t e d to volume and particles present allowed to s e t t l e overnight before analysis.  using  The AAS a n a l y s i s a nitrous oxide  was —  done a c c o r d i n g to acetylene flame.  standard  procedure  APPENDIX  Composition  C Mn P S Si Ni Cr Mo V Cu Al Co Ca 0  of  -  STEEL  Electrode  COMPOSITIONS  Steels  (weight  %)  Y_l  V2  V3  V4  V5  V6  .41 1 .20 .009 .0050 .29 1 .88 .85 .25 .01 .07 .030  .24 .46 .011 .0060 .12 2.64 1 . 44 .57 .10 .18 .030 .05 .0063 .0068  . 1 7 1 .06 .007 .0070 .21 .36 2.19 .94 .01 .19 .026 .02 .0060 .0060  .31 1.14 .010 .0037 .29 1.81 .84 .48 .07 .18 .053 .03 .0062 .0069  .42 1 .08 .007 .0015 1 .68 1 .86 .94 .40 .08 .18 .023 .03 .0030 .0054  .39 .40 .022 .0023 1 .00 .31 5.02 1 .25 .92  (weight  %)  -  .0029 .0066  Composition V1R C Mn P S Si Ni Cr Mo V Cu Al Co Ca 0  C  -  .001 5  -  .017  -  .0006 .0022  V2R .25 .31 .012 .0052 . 13 2.69 1 .45 .59 .10 .17 .024 .05 .0005 .001 4  of  Ingot V3R  .17 .70 .006 .0060 .21 .36 2.20 .95 < . 01 .17 .022 .02 .0007 .0021  Steels V4R  V5R  .32 .83 .009 .0031 .27 1 .79 .83 .48 .07 .16 .034 .03 .0006 .001 4  .42 .78 .009 .0012 1 .70 1 .87 .95 .41 .08 .17 .021 .03 .0008 .0016  -  .024  -  . 0020 . 0032  V6R .36 .31 .022 .0021 1 .00 .31 5.02 1 .25 .92  -  .024  -  .0002 .0025  APPENDIX D - UNCERTAINTY OF CHEMICAL ANALYSIS  u n c e r t a i n t y of the chemical a n a l y s i s i s : Oxygen Sulphur Aluminum Calc ium  + 5 ppm + 5 ppm +.005 weight % + 3 ppm  

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