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Removal of calcium containing inclusions during vacuum arc remelting 1983

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REMOVAL OF CALCIUM CONTAINING INCLUSIONS DURING VACUUM ARC REMELTING by EVA SAMUELSSON M.Sc, Royal Institute 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 Metallurgical Engineering We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November 1983 © Eva Samuelsson, 1983 In presenting t h i s thesis in p a r t i a l fulfilment of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t freely available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his or her representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Metallurgical Engineering The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V 6 T 1W5 Date: 15 November 1983 i i Abstract The mechanism of removal of calcium containing inclusions in s t e e l during Vacuum Arc Remelting has been investigated. Laboratory Electron Beam and i n d u s t r i a l Vacuum Arc remelting electrodes and ingots were examined. Properties of the steels were determined with the aid of chemical and metallographic methods. It is proposed that the major mechanism of removal i s rejection of calcium aluminates to a free surface. One t h i r d of the calcium sulphide is rejected with the calcium aluminates. The remainder reacts with aluminium oxide in the aluminates according to the following reaction: CaS + 1/3A1203= CaO + 2/3[Al] + [S] Subsequently, the calcium oxide i s also rejected and the dissolved sulphur reacts with sulphide forming elements during s o l i d i f i c a t i o n . The f i n a l calcium content of the remelted steels, 5 - 1 0 ppm, was independent of the calcium content of the electrode. The results of t h i s study are not in agreement with previous work, which attempts to establish the composition of the calcium aluminates as a function of the steel content of sulphur, aluminium and calcium. S p e c i f i c a l l y i t i s found that i i i the influence of oxygen content has not previously been s u f f i c i e n t l y taken into account. iv Table of Contents Abstract i i L i s t of Tables v L i s t of Figures v i Acknowledgements v i i I. INTRODUCTION 1 1 .1 Objectives 3 1 .2 Methods 3 II. LITERATURE REVIEW 4 2.1 Ladle Treatment Of Steel 4 2.1.1 Ladle Injection 5 2.1.2 Wire Injection 6 2.1.3 Conventional Alloy Addition 6 2.2 Remelting Under Vacuum 7 2.2.1 Vacuum Arc Remelting 8 2.2.2 Electron Beam Remelting 10 2.3 Inclusion Shape Control 11 2.3.1 Inclusion Modification With Calcium 12 2.4 Thermodynamic Properties 18 2.4.1 Calcium Metal 18 2.4.2 Calcium In Steel 18 2.4.3 Calcium Aluminates 20 2.4.4 Calcium Sulphide 22 2.5 Evaporation Rate 22 II I . EXPERIMENTAL PROCEDURES .' 24 3.1 Samples •. 24 3.1.1 Industrial Samples 24 3.1.2 Laboratory Samples 24 3.2 Analysis 27 3.2.1 Metallographic Examination 27 3.2.2 Bulk Steel Composition 28 3.2.3 Inclusion Extraction 29 IV. RESULTS AND DISCUSSION 30 4.1 Thermodynamic Considerations 30 4.2 Electron Beam Remelting 34 4.3 Industrial VAR Samples 35 4.4 General Observations Related To Calcium Treated Steels 40 4.4.1 Calcium Aluminate Composition 41 4.4.2 Inclusions In The Liquid Steel 42 V. CONCLUSIONS 45 BIBLIOGRAPHY 47 APPENDIX A - NOTATION 51 APPENDIX B - DETERMINATION OF CALCIUM IN STEEL BY ATOMIC ABSORPTION SPECTROPHOTOMETRY 52 APPENDIX C - STEEL COMPOSITIONS 53 APPENDIX D - UNCERTAINTY OF CHEMICAL ANALYSIS 54 V L i s t o f T a b l e s 1 . V A R m e l t i n g c o n d i t i o n s 24 2 . E B r e m e l t i n g c o n d i t i o n s l l 3 . D e s c r i p t i o n o f t h e h y p o t h e t i c a l s t e e l 33 4 . S u m m a r y o f a n a l y s i s . V x m a r k e d s a m p l e s d e n o t e s e l e c t r o d e s t e e l s , a n d V x R m a r k e d s a m p l e s a r e c o r r e s p o n d i n g r e m e l t e d i n g o t s 38 5 . R e s u l t s o f m a s s b a l a n c e s 39 v i L i s t o f F i g u r e s 1 . S c h e m a t i c o u t l i n e o f t h e V A R p r o c e s s 8 8 2 . C r o w n r e g i o n o f a V A R 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 t o t h e i n g o t p e r i p h e r y 8 9 3 . 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 o f s o m e o x i d e s i m p o r t a n t i n s t e e l m a k i n g 13 4 . 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 o f s o m e s u l p h i d e s i m p o r t a n t i n s t e e l m a k i n g 13 5 . S c h e m a t i c r e p r e s e n t a t i o n o f m o d i f i c a t i o n o f i n c l u s i o n s w i t h C a - t r e a t m e n t 1 . . . . 14 6 . T h e 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 p h a s e d i a g r a m " 4 16 7 . C o m p o s i t i o n o f c a l c i u m a l u m i n a t e s a s a f u n c t i o n o f s t e e l c a l c i u m c o n t e n t . H i l t y a n d F a r e l l 2 1 , - - - H a i d a e t . a l . 2 2 16 8 . T h e 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 — m a n g a n e s e s u l p h i d e p h a s e d i a g r a m 2 5 17 9 . D i a m o n d p y r a m i d h a r d n e s s v e r s u s t e m p e r a t u r e f o r s o m e ( M n , C a ) S s o l i d s o l u t i o n s 2 5 17 1 0 . S c h e m a t i c f i g u r e s h o w i n g w h e r e s a m p l e s a n d e l e c t r o d e s f o r E B m e l t i n g w e r e c u t f r o m i n d u c t i o n f u r n a c e i n g o t s . 26 11.. T h e E l e c t r o n B e a m f u r n a c e a t U B C 26 1 2 . S c h e m a t i c d e s c r i p t i o n o f t h e p r o b l e m s w i t h m i c r o p r o b e a n a l y s i s . N o t e t h a t a l l t h r e e i n c l u s i o n s g i v e t h e s a m e 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 1 3 . E v a l u a t i o n o f t h e t h e r m o d y n a m i c d r i v i n g f o r c e . 34 1 4 . " B e a d " 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 o f E B - m e l t e d i n g o t . T h e b l a c k p a t c h e s a r e C a S a n d t h e b u l k p h a s e i s C x A y . 3 6 . 1 5 . 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 a n 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 " b e a d " 36' 1 6 . C o a l e s c e d i n c l u s i o n s o n a n e l e c t r o d e t i p . L i g h t m i c r o s c o p e a n d S E M X - r a y i m a g e s 3 7 r 1 7 . C o m p o s i t i o n o f c a l c i u m a l u m i n a t e s a s a f u n c t i o n o f s t e e l c a l c i u m c o n t e n t . E x p e r i m e n t a l r e s u l t s , a n d r e s u l t s f r o m H i l t y & F a r e l l 2 1 a n d H a i d a 2 2 41* 1 8 . 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 s t e e l . L i g h t m i c r o s c o p e a n d S E M X - r a y i m a g e s ,43 v i i Acknowledgement I would l i k e to thank Dr Alec M i t c h e l l for his guidance and time spent on many helpful discussions. The contribution of samples from my colleagues in the industry was essential for the project and i s much appreciated. The assistance of the technical staff at the Metallurgy department, p a r t i c u l a r l y Gus Sidla, Rudy Cardeno, Mary Mager and Laurie Frederick is gr a t e f u l l y acknowledged. I would also l i k e to thank my fellow gratuate students for their friendship and many interesting discussions. Economic assistance from the Natural Sciences and Research Council of Canada is gr a t e f u l l y acknowledged. F i n a l l y I would l i k e to thank my husband, Fred Bradley, for his encouragement and many helpful suggestions. 1 I. INTRODUCTION The production of qu a l i t y steels for demanding applications, such as a i r c r a f t landing gears, requires tight control of hydrogen content, quantity and composition of non- metallic inclusions, and metallurgical structure in order to ensure mechanical soundness. Two remelting processes, Vacuum Arc Remelting (VAR) and Electro Slag Remelting (ESR), are commonly used to manufacture these ste e l s . The ESR process i s characterized by the remelting of an electrode through a refin i n g slag, generally under atmospheric conditions. An advantage of the process i s that the content and nature of the non-metallic inclusions can be controlled, to some extent, through manipulation of the slag-metal reactions. A desirable metallurgical structure can be attained by monitoring the rate of ingot s o l i d i f i c a t i o n in the water-cooled copper mould. Special precautions must be taken to avoid hydrogen pick-up during r e f i n i n g . In North America, for h i s t o r i c a l reasons, regulations state that many of these steels must be produced using the VAR process. In contrast to the ESR process, in the VAR process an electrode is remelted under vacuum conditions without the benefit of a r e f i n i n g slag. The vacuum processing ensures a low hydrogen content. In a similar way to the ESR process, the ingot s o l i d i f i c a t i o n structure can be controlled, although the remelting rate i s not as e a s i l y monitored due to problems of arc i n s t a b i l i t y . Due to the lack of slag r e f i n i n g , the electrode 2 material must be well desulphurized prior to remelting, since vacuum reactions do not result in s i g n i f i c a n t desulphurization. Many techniques for the desulphurization of steels, prior to casting the VAR electrode, are available. While t r a d i t i o n a l l y desulphurization in the e l e c t r i c arc furnace has been used for thi s purpose, the recent trend i s to ladle desulphurize with calcium or calcium-containing compounds. The advantages associated with ladle treatment are increased furnace production at lower cost and desulphurization to lower levels than are possible in e l e c t r i c arc furnace steelmaking without the dangers of phosphorus reversion or aluminium pick-up. In addition to desulphurization the calcium treatment provides inclusion shape control for the electrode s t e e l . Although i t i s commonly accepted that much of the calcium i s los t during remelting, calcium treatment i s known to be be n e f i c i a l for the mechanical properties of the product. Almost a l l of the calcium i s bound in the s o l i d i f i e d s t e e l as either sulphide or oxide. From the apparent contradiction one could draw the conclusion that deleterious elements are removed with the calcium during remelting. While stochiometric evaporation of calcium sulphide has been suggested as a possible explanation, other mechanisms could operate, for instance mechanical removal by buoyancy or f l u i d flow. F i n a l l y , from an economic point of view the question arises as to whether the content of calcium in the electrode has a di r e c t influence on the steel quality after remelting. Since calcium treatment i s 3 an e x p e n s i v e p r o c e s s a n d t h e p r e s e n c e o f c a l c i u m r e q u i r e s e x t e n s i v e p r e c a u t i o n s t o p r e v e n t r e o x i d a t i o n d u r i n g e l e c t r o d e c a s t i n g , i t i s a d v a n t a g e o u s t o d e f i n e p r e c i s e l y how much c a l c i u m , and i n what f o r m , i s r e q u i r e d i n t h e e l e c t r o d e . 1.1 O b j e c t i v e s The m a j o r o b j e c t i v e s o f t h i s s t u d y a r e t o d e t e r m i n e t h e r e m o v a l m e c h a n i s m 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 , a n d t o s t u d y t h e i n f l u e n c e o f t h e e l e c t r o d e c a l c i u m c o n t e n t on t h e f i n a l i n g o t c o m p o s i t i o n , p a r t i c u l a r l y a s i t r e l a t e s t o t h e c o m p o s i t i o n o f 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 . 1.2 M e t h o d s I n d u s t r i a l VAR s a m p l e s a n d l a b o r a t o r y E l e c t r o n Beam r e m e l t e d s a m p l e s have been i n v e s t i g a t e d . P r o p e r t i e s o f t h e s t e e l s h ave been d e t e r m i n e d w i t h t h e a i d o f c h e m i c a l a n d m e t a l l o g r a p h i c m e t h o d s . The t h e r m o d y n a m i c d r i v i n g f o r c e f o r p o t e n t i a l c h e m i c a l r e a c t i o n s was d e t e r m i n e d t o i n t e r p r e t t h e e x p e r i m e n t a l e v i d e n c e . 4 II. LITERATURE REVIEW 2.1 Ladle Treatment Of Steel The increased demand for high quality steels, the introduction of the Ultra High Power e l e c t r i c furnaces and the BOF processes used in conjunction with continuous casting make secondary steelmaking more a t t r a c t i v e for the steelmaking companies. As a result, a large number of secondary steelmaking procedures have been developed during the l a s t twenty years. Here, only those processes which are used for calcium treatment w i l l be discussed. The two major purposes of calcium treatment of steels are desulphurization and inclusion shape control. The desulphurization is due to the high a f f i n i t y of calcium for sulphur. The resulting inclusions are l i g h t and f l o a t e a s i l y to the slag. In addition, the calcium treatment increases the sulphur capacity of the slag. The second consequence of calcium treatment, inclusion shape control, w i l l be discussed in section 2.3. The physical properties of calcium, low density and high vapour pressure at steelmaking temperatures, prevent the use of simple addition methods of pure calcium to s t e e l . Therefore, more elaborate techniques such as powder in j e c t i o n and wire injection have been developed. Another alternative i s to add calcium in the form of an a l l o y . 5 The low s o l u b i l i t y of calcium in steel may also cause problems. With the more sophisticated addition techniques i t is possible to reach contents high enough for sat i s f a c t o r y desulphurization and inclusion shape control. However, care must be taken not to reoxidize the steel during teeming to such an extent that the inclusion shape control diminishes. 2.1.1 Ladle Injection Holappa 1 has summarized the published work concerning ladle i n j e c t i o n metallurgy. Ladle i n j e c t i o n , which i s the newest ladle process, was developed mainly as a rapid desulphurization method. The process also provides a means to introduce calcium in the s t e e l , with subsequent deoxidation and inclusion shape contr o l . The equipment for inje c t i o n consist of powder dispensers connected to a lance that can be immersed into the s t e e l . During i n j e c t i o n , the powder i s f l u i d i z e d in the dispenser by a c a r r i e r gas, usually argon. The powder — gas mixture i s then injected deeply into the s t e e l . Thus, one of the main advantages with ladle i n j e c t i o n is that l i g h t a l l o y additions are given s u f f i c i e n t time to melt and react with the s t e e l . The second p r i n c i p a l feature of ladle i n j e c t i o n i s the vigorous s t i r r i n g that the inje c t i o n causes. The s t i r r i n g has the advantage of creating a large contact area between st e e l and slag, but i t also causes problems with reoxidation reactions with the ladle l i n i n g . Therefore ladles used for injection 6 treatment are lined with highly stable r e f r a c t o r i e s such as dolomite, magnesite and high alumina. For calcium treatment, the most commonly used powders are calcium s i l i c i d e (~30% Ca), calcium carbide (~80% CaC 2) and d i f f e r e n t slag mixtures consisting of CaO, CaF 2 and A l 2 0 3 . 2.1.2 Wire Injection An alternative to the powder injec t i o n technique i s wire " i n j e c t i o n " of calcium into the l a d l e 2 , 3> *. By protecting the calcium wire with a steel layer, the calcium can be prevented from reacting prematurely with a i r or slag. The wire i s fed at high speed (80-300 m/min) into the s t e e l . Less than 1.5 m f e r r o s t a t i c head is required to suppress the b o i l i n g of calcium at steelmaking temperatures. Since the stee l c l a d wire w i l l melt in 1 - 3 seconds, the system permits l i q u i d calcium to react with the s t e e l before evaporation of remaining calcium occurs. Economically, powder injection demands a higher i n i t i a l investment whereas the cost per added unit calcium is higher for wire " i n j e c t i o n " . 2.1.3 Conventional Alloy Addition Calcium has considerably higher s o l u b i l i t y in s i l i c o n and nickel than in iron. This fact allows the production of high calcium a l l o y s which are l a t e r used for adding calcium to s t e e l . As the a c t i v i t y of calcium i s lowered in these a l l o y s , the reactions with steel become less v i o l e n t , and a higher recovery is obtained. A serious disadvantage of t h i s kind of treatment 7 i s the introduction of additional elements, which may not always be desirable. Therefore, some companies even add "logs" of metallic calcium covered by s t e e l . The problem with t h i s technique is the violent reaction that occurs when larger amounts of calcium come in contact with the s t e e l . 2.2 Remelting Under Vacuum At present, two processes are available for remelting under vacuum. These are Vacuum Arc Remelting (VAR) and Electron Beam (EB) melting. If the EB furnace i s constructed for remelting, then the VAR and EB melting processes are very s i m i l a r . In both processes some chemical impurities are removed by the exposure of the molten metal to vacuum and the continuous s o l i d i f i c a t i o n ensures a-controlled s o l i d i f i c a t i o n structure. The fundamental . difference i s the heat sources, either an electron beam or a vacuum arc. In addition the pressure in the EB process i s generally lower, and the melting speed independent of the power input. Krone, 5 Kazakov 6 and Wahlster 7 have compared the EB and VAR processes. The conclusion of their comparison i s that due to the slower melting speed the EB melted materials w i l l lose more a l l o y i n g elements and impurities than the VAR melted materials. The EB and VAR processes w i l l now be discussed in more d e t a i l . 8 2.2.1 Vacuum Arc Remelting The Vacuum Arc Remelting (VAR) process i s schematically outlined in Figure 1 8 . The equipment consists of a water-cooled copper crucible, an enclosure connected to a vacuum pumping system, a DC power supply, machinery to move the electrode and process control instrumentation. A more detailed description of the VAR process i s given by M i t c h e l l 8 . During remelting an e l e c t r i c arc between ingot and electrode supplies the heat for melting. Molten drops from the electrode t i p successively f a l l into the l i q u i d pool, and heat removal for s o l i d i f i c a t i o n occurs through the s o l i d i f i e d ingot and cruc i b l e . Thus, removal of impurities by evaporation is possible from two surfaces, the electrode t i p and the molten pool. In addition, s o l i d or l i q u i d DC. Power Supply Vacuum Pump Water in Figure 1 - Schematic outline of the VAR process 8. 9 i m p u r i t i e s can be removed by the f l u i d f l o w and/or buoyancy from the molten p o o l t o the s u r f a c e of the i n g o t . Krone e t . a l . 5 , P o v o l o t s k i i e t . a l . 9 , and M i t c h e l l 8 have d i s c u s s e d the removal of n o n - m e t a l l i c i n c l u s i o n s from s t e e l d u r i n g Vacuum Arc R e m e l t i n g . I t has been suggested 8' 9 t h a t the n o n - m e t a l l i c i n c l u s i o n s on the p o o l s u r f a c e are m e c h a n i c a l l y removed, by e i t h e r f l o a t i n g t o the edge of the p o o l or b e i n g s p l a t t e r e d on the "crown" of the i n g o t . F i g u r e 2 shows the top edge of a VAR i n g o t c o n t a i n i n g n o n - m e t a l l i c i n c l u s i o n s . P o v o l o t s k i i 9 a l s o found t h a t u n s t a b l e i n c l u s i o n s such as S i 0 2 a r e reduced by carbon but t h a t corundum i s not a f f e c t e d . The p r e s s u r e at the molten s u r f a c e s c o u l d be as much as F i g u r e 2 - Crown r e g i o n of a VAR i n g o t which 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 t o the i n g o t p e r i p h e r y 8 . 10 three orders of magnitude higher than that measured at the head of the pumping system 5. This is reasonable, since the vapour pressure of iron alone i s an order of magnitude higher at 1600°C than the "operating pressure" of 1X10~3 — 5X10" 3 t o r r . It i s also known that Mn, which at remelting temperature i s present in solution, not as sulphide, does evaporate to a large extent. 2.2.2 Electron Beam Remelting As mentioned, the p r i n c i p a l difference between VAR and EB remelting is the heat source. The EB process has been described by S c h i l l e r 1 0 . Apart from the heat source, the other major difference between the two processes is the melting chamber pressure, which i s around 10~2 torr for an i n d u s t r i a l EB furnace. The lower chamber pressure i s maintained to assure stable operation of the gun, which requires a pressure of 10"" torr or lower. The removal of a l l o y i n g elements and impurities has been discussed by Krone 5 and Doenecke 1 1. Doenecke 1 1 suggests that manganese and sulphur are removed by evaporation, and oxygen according to the reaction [C] + [0] = CO(g). However, he does not, by either calculations or experimental r e s u l t s , prove the mechanisms of removal of either oxygen or sulphur. 11 The removal mechanism of non-metallic inclusions from steel during EB melting has not been discussed in any d e t a i l in the l i t e r a t u r e . However, EB-melting has been used for non-metallic inclusion assessment of superalloys 1 2- 1 3 . This technique is based on the fact that the l i g h t inclusions f l o a t to the surface of the ingot where they can later be c o l l e c t e d . S u t t o n 1 3 claims that the alumina inclusions can be recovered down to the la s t 1 — 2 ppm using t h i s method. 2 . 3 Inclusion Shape Control The morphology and composition'of indigenous inclusions, as well as their influence on mechanical properties, has been described by several a u t h o r s 1 " " 1 6 . The inclusion picture of a steel is d i r e c t l y related to the deoxidati.on practice. High grade steels are f u l l y k i l l e d , usually ' with aluminium. Unfortunately, the aluminium oxide forms hard, angular inclusions which frequently gather in c l u s t e r s . These alumina cl u s t e r s can be deleterious for the mechanical properties of the s t e e l . In addition, aluminium deoxidation promotes the formation of manganese sulphide type I I . As a result of the adverse influence of alumina clusters and type II MnS alt e r n a t i v e deoxidation practices have been developed. These practices u t i l i z e calcium, the rare earth metals, zirconium or titanium. However, in a l l cases i n i t i a l ladle deoxidation is usually performed with aluminium. This practice increases the y i e l d of the expensive elements which are used for inclusion modification. Here, only inclusion modification with calcium 1 2 w i l l be discussed. 2.3.1 Inclusion Modification With Calcium Calcium i s among the strongest oxide and sulphide formers of the elements as can be seen in Figures 3 and 4. Therefore, i t w i l l modify existing oxides and i t also prevents the formation of MnS type II. The change in inclusion morphology and composition between an untreated and a calcium treated steel is schematically i l l u s t r a t e d in Figure 5. Different explanations have been given for the mechanism of formation of the three types of MnS in s t e e l 1 " ' 1 7 ~ 1 9 . MnS type I inclusions are found in rimmed or semikilled steels and are of a spherical shape. It i s reasonably well agreed that i t forms by a monotectic reaction in the interdendritic region during s o l i d i f i c a t i o n . Type II MnS inclusions are rodlike and found in colonies as "fences" or "fans" in k i l l e d s t e e l s . When the metal i s worked the type II inclusions form almost continuous sheets of MnS which are p a r t i c u l a r l y deleterious for the mechanical properties. T r a d i t i o n a l l y , type II was assumed formed by an eutectic reaction, but later investigations indicate that i t forms by a cooperative monotectic reaction. MnS type III inclusions are angular and the formation i s promoted by a l l o y elements such as C, Cr, Ca and excess A l . It has been suggested that the a l l o y elements change the phase diagram, the result being that MnS is precipitated as a s o l i d proeutectoid phase. In that case the inclusions would fl o a t out of the melt l i k e other l i g h t inclusions. Since t h i s phenomenon 1 3 Figure 3 - Standard free energy of formation of some oxides important in steelmaking. TEMPERATURE, 'C 0 500 1000 1500 2000 > Figure 4 - Standard free energy of formation sulphides important in steelmaking. of some 1 4 Figure 5 - Schematic representation of modification of inclusions with Ca-treatment 1 has not been observed the mechanism of formation i s probably di fferent. Salter and P i c k e r i n g 2 0 and H i l t y and F a r e l l 2 1 have investigated the transformation of indigenous inclusions after addition of calcium to the s t e e l . Calcium in solution reacts with alumina present to form calcium aluminates, the composition of these being dependent on several elements in the s t e e l . As seen in Figure 6, the calcium aluminates formed w i l l be l i q u i d at steelmaking temperatures i f the calcium oxide content of the oxide phase i s between 36 and 68 weight %. However, even lower t o t a l CaO content can produce round hard inclusions, since the content of aluminium frequently decreases toward the periphery of the i n c l u s i o n 2 0 . H i l t y and F a r e l l 2 1 and Haida e t . a l . 2 2 have 15 suggested that the composition of aluminates i s related to the steel composition according to Figure 7. The aluminate composition would then be dependent on only sulphur and calcium content at constant aluminium content. However, since the content of oxygen also changes in the same di r e c t i o n as sulphur in these investigations, i t i s probable that the relationship i s more complex. Faulring and Ramalingam 2 3 have proposed an inclusion p r e c i p i t a t i o n diagram as an aid in determining which aluminates w i l l form. Unfortunately, due to the lack of thermodynamic data for calcium in steel solutions the diagram i s given in terms of Henrian a c t i v i t i e s . In addition, their applied thermodynamic data for the calcium aluminate system appears to be erroneous 2". Calcium sulphide i s usually found as a peripheral rim around calcium aluminates with calcium content equal to or higher than CA 2. As can be seen in Figure 8 the CaS has a s o l i d s o l u b i l i t y of MnS of about 10 mole %, and MnS has a s o l i d s o l u b i l i t y of about 14 mole- % CaS. Any "high content MnS" found in calcium treated steels are of type III, and the deleterious type II i s e n t i r e l y eliminated. In addition to the more advantageous shape, the sulphides for calcium-treated steels are also harder than those in untreated steels, as seen in Figure 9 2 5. However, the transformation of sulphides may not be only advantageous. It has been suggested that calcium sulphides are detrimental to the corrosion resistance of s t e e l 2 6 ' 2 7 . 16 2100 2000 1900 1800 TEMP °C 1700 1600 1500 1400 1300 CQO 1 1 • — I — i 1 1 i To CaO MP / Liquid \ /Liq. 6 - CaO + Liquid —\ \—| CaO + C A . Liquid /XA, / Liquid - Liquid VUqUid CA2 + CA C > CA 2 Al,03 CA6- 1 1 1 C3A + CA • • C3A CA CAj CA6 Al203 0 10 20 30 40 50 60 70 80 90 100 Weight % Al 20 3 Figure 6 - The pseudo binary calcium oxide - aluminium oxide phase diagram"". j i i i_ 12Ca0 7AI203 CaO Al203 Ca0-2AI203 Ca06Al203 0 10 20 30 40 50 60 70 CALCIUM content of steel, ppm. 80 90 Figure 7 - Composition of calcium aluminates as a function of steel calcium content. H i l t y and F a r e l l 2 1 , Haida e t . a l . 2 2 . 1 7 2 4 0 0 K 2 2 0 0 2 0 0 0 1800 T E M P o C 1600 1400 \ T 1 1 r- LIQUID 161C (Co, Mn)S 0 20 40 60 80 100 CaS MnS Mole % MnS Figure 8 - The pseudo binary calcium sulphide sulphide phase diagram 2 5. — manganese 2 0 0 HARDNESS kg./mm.2 100 I I ' 1 ' I 1 I ' ^ " ^ ^ - ^ g ^ o C o S - \ >w ^ ^ ^ 0 m / o C a S - — \ X . ^ • ^ ^ C a S - ^ ^ ^ 2 %CQS_ i . ^ ^ - ^ . . P u r e MnS I . I . I . 0 0 200 400 600 800 T E M P E R A T U R E , °C Figure 9 -Diamond pyramid hardness versus temperature for some(Mn,Ca)S s o l i d s o l u t i o n s 2 5 . 18 2.4 Thermodynamic Properties 2.4.1 Calcium Metal The thermodynamic data for pure calcium are well established and have been compiled by Kubashewski 2 8 and in the JANAF t a b l e s 2 9 . Vapour pressure data have been evaluated by Schurmann 3 0 at a later date. Calcium has a melting point of 839°C and a b o i l i n g point of 1494°C 2 9. The vapour pressure is given by the following equation between 1200 and 1700°C 3°: 18482 ln p°= 10.48 - (p in atm, T in K) ... (2.1) T 2.4.2 Calcium In Steel Numerous attempts have been made to establish the thermodynamic properties of calcium in iron s o l u t i o n s 3 1 " 3 7 . In addition, several compilations or comparisons of data e x i s t 3 8 - " 1 . The reactions of interest are: CaO(s) = [Ca] + [0] ... (2.2) CaS(s) = [Ca] + [S] ... (2.3) These reactions can be obtained by combining the following reactions: 19 CaO(s) = Ca(l) + 1/202 CaS(s) = Ca(l) + 1/2S2 l/20 2(g) = [0] l/2S 2(g) = [S] Ca(l) = [Ca] (2.4) (2.5) (2.6) (2.7) (2.8) The equilibrium constants for reactions 2.4 to 2.7 are reasonably well-known 2 8- 2 9 i 3 9 . S p o n s e l l e r 3 1 measured the s o l u b i l i t y of calcium in l i q u i d steel in equilibrium with l i q u i d pure calcium. Based on th i s maximum s o l u b i l i t y of 0.032 weight %, an equilibrium constant for reaction 2.8 can be calculated. The data of Sponseller also y i e l d a Raultian a c t i v i t y c o e f f i c i e n t , ii£a , of 2270 for calcium in pure iron solution. However, Sponseller 3' did not consider the oxygen and sulphur in the "pure" iron solution. Thus, part of the calcium "soluble" in iron was probably bound as sulphide or oxide. This would mean that the actual s o l u b i l i t y of calcium in iron is lower than the value given by Sponseller. However, as other data are lacking i t w i l l be applied to calculate the equilibrium constant for reactions 2.2 and 2.3. At 1600°C t h i s y i e l d s : K2.2 = 5.3 x 10 K2.3 = 1.6 x 10"9 1 1 ... (2.9) ... (2.10) Corresponding interaction c o e f f i c i e n t s have been suggested for the calcium oxygen interaction assuming that the s e l f - interaction c o e f f i c i e n t for calcium i s zero, eoQ = -535 and 20 ec°Q= -1330. A d i f f e r e n t approach has been taken by several other w o r k e r s 3 3 " 3 7 . They assume that a l l non-metallic inclusions have been removed from a steel melt in contact with CaO or CaS after a certain time. Thus, the chemically analysed content of calcium in the quenched steel i s assumed equal to that in solution. This approach yie l d s "an apparent equilibrium constant", K*2.2 or K*2.3, which i s coordinated with interaction parameters. One such set of values i s given by Gustafsson 3 f l. K*2.2 = 4.5 x 10" B; K*2.3 = 3.2 x 10" 7; 2.4.3 Calcium Aluminates Due to the importance of the c a l c i a alumina system in cement technology, geology and metallurgy, several authors have discussed i t s thermodynamic p r o p e r t i e s " 2 " 5 1 . In spite of t h i s fact, the thermodynamic data for the system are s t i l l not well established. For instance, recent l i t e r a t u r e values 2 9' 5 2 for the seemingly simple property of melting temperature of CaO, vary between 2580°C and 2950°C. Thus, a l l thermodynamic calculations connected to the melting point could introduce errors. Ca e 0 = -150 ef = -110 - ... (2.11) ... (2.12) 21 An e f f o r t has been made to determine the most recent available thermodynamic data. The phase diagram for the pseudo- binary CaO - A I 3 O 3 system as given in Figure 6 was determined by Nurse e t . a l . u , The phase C 1 2A 7 i s stable only in the presence of water or halogens""' " 9 and is not included in t h i s diagram. E l i e z e r e t . a l . 5 0 have evaluated l i t e r a t u r e data and suggested R e d l i s h - K i s t e r 5 3 c o e f f i c i e n t s for the enthalpy of mixing for l i q u i d calcium aluminates and for the a c t i v i t y c o e f f i c i e n t . The integral enthalpy of mixing for the l i q u i d CaO-AlOLs system i s given by H = X 1X 2[-123.16 + 41.79(X,- X 2) + 30.80(X 1- X 2 ) 2 - 27 . 06(X,-X2 ) 3 ] , ... (2.13) where X, (or X 2) i s either X C q Q or xAIO1 5 * T ^ e a c t i v i t y c o e f f i c i e n t for the same system at 1000K, with l i q u i d pure oxides as standard state i s given by loqf,= X 2[-5.885 + 1 . 1 45 ( 3X, - X 2 ) +.723(X,+ X 2 )(5X 1- X 2 ) -.610(X,- X 2) 2(7X,- X 2) +.493(X,- X 2) 3(9X,- X 2)] ... (2.14) This a c t i v i t y c o e f f i c i e n t , corrected for temperature and standard state w i l l be used in the calculations involving calcium aluminates together with fusion data from JANAF2 9 . The most recently published experimental data of t h i s system are those of Lourtau e t . a l . " 9 . They determined a c t i v i t i e s of CaO and A l 2 0 3 in order to obtain the free energies 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 for the system. 2.4.4 Calcium Sulphide The thermodynamic data for CaS have been taken exclusively from JANAF2 9 . Simi l a r l y , as with CaO, data related to the melting of CaS may not be r e l i a b l e due to the high melting point. 2.5 Evaporation Rate In a good vacuum (p < 10"3 atm) the evaporation rate from the surface of a metal melt i s described by the Langmuir equat ion 54 " 5 8 : m = 44.33St /M/T YxpV ' ... (2.15) This equation shows that the evaporation rate i s independent of t o t a l pressure but dependent on evaporation area, time of exposure and temperature. If almost a l l calcium i s bound as either CaS or C xA y, evaporation of calcium in solution w i l l occur from a very d i l u t e solution. A sample ca l c u l a t i o n shows that for r e a l i s t i c VAR melting conditions, (A = 3700 cm2, T = 1600°C) an amount in excess of 1 ppm calcium would hypothetically evaporate, assuming that the Henrian a c t i v i t y in the steel i s 0.1 ppm. Thus, the rate l i m i t i n g step w i l l not be evaporation of calcium from solution, but rather the reaction of the inclusion compounds 23 present on the sur face g i v i n g r i s e to the c a l c i u m in s o l u t i o n . 24 II I . EXPERIMENTAL PROCEDURES 3.1 Samples Two types of samples were investigated. Samples from corresponding electrode and VAR ingots were obtained from three d i f f e r e n t companies. To supply additional data, laboratory samples produced with the aid of the induction and electron beam furnaces at UBC were prepared. 3.1.1 Industrial Samples The i n d u s t r i a l l y produced steels were of the high-strength low-alloy type. In a l l cases, the electrode steels were ladle treated with calcium, either by direct addition of "Ferrocalcium" or by wire addition. The steels were Va,cuum Arc Remelted under approximately the conditions given in Table 1. 3.1.2 Laboratory Samples The laboratory electrodes were prepared in a five kilogram induction furn-ace. Magnesia cru c i b l e s were used to avoid pickup of impurities. The i n i t i a l charges of "Armco iron" were melted Table 1 - VAR melting conditions Electrode diameter: Ingot diameter: Melting rate: Pool temperature: 1500 - 1680°C 470 mm 500 mm 300 kg/hr Note: Parabolic d i s t r i b u t i o n . Operating pressure: 10"3 - 5X10" 3 torr 25 under a shield of argon. When the entire charge was molten, preliminary deoxidation was performed by s t i r r i n g the melt with graphite rods. Appropriate amounts of the a l l o y additions, ferromanganese, iron sulphide and aluminium were added. F i n a l l y calcium metal was added by plunging p e l l e t s wrapped in iron f o i l into the melt. The melts were then allowed to s o l i d i f y in the c r u c i b l e . Unfortunately, melts poured into a mould before s o l i d i f i c a t i o n did not contain the desirable types of inclusions. This could have been due to excessive reoxidation. In some cases, pin samples of a diameter of 4.2 mm were taken from the bath, in order to study the inclusions in the l i q u i d melt. The melting procedure produced a c y l i n d r i c a l ingot. Samples- for analysis were cut from the middle of the ingot in such a manner as to avoid the areas associated with the outside surface and s o l i d i f i c a t i o n shrinkage (see Figure 10). One or several electrodes for subsequent Electron Beam remelting were cut along the cyl i n d e r . The electrodes were remelted in a 15 kW laboratory electron beam furnace u t i l i z i n g a gun manufactured by the Manfred von Ardenne Research I n s t i t u t e 1 0 . The furnace i s shown in Figure 11. The conditions for remelting are given in Table 2. An arrangement of mirrors made i t possible to watch the melt in progress. 26 Figure 11 - The Electron Beam furnace at UBC. 27 Table 2 - EB remelting conditions Electrode crossection: Melting rate: Melt s i z e : Operating pressure: 2.2 - 4 cm2 0.7-1 kg/hr 200 g 10-* torr 3.2 Analysis 3.2.1 Metallographic Examination Sections of both electrode and ingot materials were ground and polished. To prevent oxidation of the calcium sulphides, contact with water was avoided during the preparation stage and the samples were stored in a d e s s i c a t o r 1 5 . General metallographic examination was done with o p t i c a l microscopy. Qualitative and semiquantitative analysis of the inclusions in s i t u was obtained by Scanning Electron Microscopy - EDX analysis. Quantitative inclusion analysis was performed for some of the samples by electron microprobe analysis. The standards for microprobe anaylsis were: Pure Mn, pure Fe, A l 2 0 3 , CaC03 and ZnS. The raw i n t e n s i t i e s were corrected using a Magic IV program. The phases frequently interfere with each other during microprobe analysis, as the calcium sulphide i s present as a peripheral rim around the aluminates. This problem i s schematically described in Figure 12. The problem can be overcome i f 5 elements (Fe, Mn, Ca, S, and Al) are analysed simultaneously. Unfortunately, the microprobe at UBC can only analyse two elements simultaneously. Therefore, most of the microprobe analysis was done on electrode materials where larger 28 POLISHED ELECTRON Figure 12 - Schematic description of the problems with microprobe analysis. Note that a l l three inclusions give the same appearance from the surface. 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 analysed. c) Only in this case can an accurate C/A r a t i o be obtained by analysing only two elements. inclusions could be found. 3.2.2 Bulk Steel Composition Bulk analysis of most elements was obtained by spectrographic analysis. The oxygen content was determined by the vacuum fusion method and the sulphur content by the combustion iodometric method according to standard procedures. The calcium contents were determined with atomic absorption spectrophotometry using a modified version of the method described by H i l t y and F a r e l l 2 1 , as described in Appendix B. 29 3.2.3 Inclusion Extraction In order to confirm the electron microprobe anaylsis and to determine the inclusion composition for the materials with inclusions too small for microprobe analysis, chemical inclusion extraction was performed. Methanol bromine extraction under dry conditions was applied according to the technique described by Reyes-Carmona 5 9. By subjecting a r t i f i c i a l calcium aluminates and calcium sulphide to the extraction, i t was determined that a mixture of C 3A and CA or pure CA do not dissolve whereas CaS does dissolve. Thus, th i s separation technique made i t possible to determine the quantity of calcium bound as oxide and as sulphide assuming that a l l calcium is bound as either sulphide or oxide in the s o l i d s t e e l . The c o l l e c t e d inclusions were transferred to aqueous solution by the lithium-metaborate method 6 0 for subsequent atomic absorption analysis. By analysing for Ca in the inclusions, the average composition of the calcium aluminates could be determined assuming that a l l oxygen was bound as calcium aluminate in the s t e e l . An attempt was made to analyse the calcium in solution from the extraction. This calcium represents the calcium bound as sulphide. Unfortunately, t h i s f a i l e d probably due to pick up of calcium from the apparatus. Another problem was the contamination of the extracted pre c i p i t a t e s by carbides. This prevented weighing of the oxide phase and made x-ray d i f f r a c t i o n very d i f f i c u l t . 30 IV. RESULTS AND DISCUSSION 4.1 Thermodynamic Considerations Calcium could be present in four phases during remelting, l i q u i d metal, s o l i d sulphide, l i q u i d or s o l i d oxide, and gas phase. Consider the equilibrium between dissolved calcium and gas at 1600°C: [Ca] = Ca(g) K=57.5 (30,31)* ... (4.1) As the t o t a l pressure does not exceed 10"3 atm during VAR remelting, and the p a r t i a l pressure of calcium can not be higher, i t follows that the a c t i v i t y of calcium in the melt according to reaction 4.1, w i l l be lower than 0.2 ppm. Therefore, calcium in the metal phase w i l l not be considered. However, i t i s possible that dissolved calcium takes part in the reactions as an intermediate species. The equilibrium constant for reaction 4.1 is probably inaccurate as pointed out in the l i t e r a t u r e review. The anticipated lower s o l u b i l i t y of calcium in steel would y i e l d an even higher Ku., . Thus, the assumption would be v a l i d also in that case. * The standard state for sulphides and oxides i s pure s o l i d compounds. The standard state for elements dissolved in iron solution i s Henrian i n f i n i t e l y d i l u t e solution. References are given in parenthesis where new equilibrium data have been applied. 31 Calcium sulphide could take part in the following reactions during vacuum remelting: CaS(s) = Ca(g) + [S](in Cx Ay ) . . . (4. 2) CaS(s) = CaS(g) • K= 6.4 X 1 0- 9(29) . . . (4. 3) CaS(s) = Ca(g) + 1/2S2 K= 2.2 X 10" 1 o(29,30) ... (4. 4) CaS(s) = Ca(g) + [S] K= 9.3 X 10- 8(39) ... (4. 5) CaS(s) + 1/3A1203 = CaO(l, in C x A y) + 2/3[Al] + [S] K= 1 .3 X 10"3 ... (4. 6) It has been shown*7 that the maxiumum s o l u b i t i l i y of sulphur in a C xA y melt containing 50 weight % CaO is 1.4 weight %. The average composition of the aluminate inclusions in a st e e l i s l i k e l y to be on the alumina r i c h side. Since these aluminates have a lower s o l u b i l i t y of sulphur, even i f reaction 4.2 takes place i t w i l l not be of quantitative importance. The equilibrium constants show that 4.5 i s most l i k e l y to occur under standard conditions. However, the pro b a b i l i t y that reactions 4.5 and 4.6 w i l l occur depends on the a c t i v i t i e s of the species. These reactions w i l l be discussed later in conjunction with other possible reactions. Possible reactions that the oxide phase could take part in are: CaO(l, in C xA y) = CaO(g) K= 6.4 x 10" 1 1 (24) ... (4.7) CaO(l, in C xA y) + [C] = Ca(g) + CO(g) 32 K= 1.5 x 10"5 ... (4.8) 1/3A1 20 3(1, in C xA y) + [C] = 2/3[Al] + CO(g) R= 2.1 x 10"' ... (4.9) Of these reactions, 4.8 and 4.9 appear most l i k e l y to occur. Further investigation of the f e a s i b i l i t y of reactions 4.5, 4.6, 4.8 and 4.9 in an i n d u s t r i a l steel requires a knowledge of the thermodynamic properties of the elements in st e e l solution. However, as mentioned in the l i t e r a t u r e review, the thermodynamic data for calcium in steel solution and i t s interaction parameters with other elements are not well established. Because of t h i s , a hypothetical steel with only carbon, aluminum and sulphur in the steel solution w i l l be discussed. The Henrian a c t i v i t i e s of the dissolved elements and the a c t i v i t i e s of CaO and A l 2 0 3 in C xA y for the "example" composition has been determined using the mentioned l i t e r a t u r e data 2 8' 2 9' 3 9' " 9- 5 1' 5 3 . The hypothetical steel i s described in Table 3. The a c t i v i t i e s in the hypothetical steel y i e l d the following r a t i o s of reaction products over reactants ("=R") for the interesting reactions: R4.5 = 2.7 x 1 0 - 6 R«.6 = 4.9 x 1 0 " 5 R«.8 = 2.5 x 1 0 " 5 R4.9 = 4.6 x 10-" (K f t 5 = 9.3 x 1 0 - 8 ) (K, s = 1.3 x 1 0 " 3 ) ( K a 8 = 1.5 x 1 0 - 5 ) (K„ 9 = 2.1 x 1 0 " 1 ) As can be seen, there i s a thermodynamic dri v i n g force for both 33 Table 3 - Description of the hypothetical steel ASSUMED PROPERTY VALUE USED IN CALCULATIONS REFERENCES METAL PHASE: Sulphur Aluminium Carbon c s =.0025wt%* c A | =.025 wt%* c c =.30 wt%* h s =.0027 h A | =.027 hQ =.33 39 39 39 INCLUSIONS: CaS(s) C X A y GAS PHASE: Calc ium CO X C Q S = 1 „' C C q 0 = 40 wt% P r = 10-3 p C o= 10-3 CO aCcS = I ^ a C a 0 = 0.12** a A l 2 0 3 = ° ' 2 1 * * P C n = 1 0 " 3 *co= 1 0 " 3 29, 49, 50 28, 49, 50 * S, Al and C are the only elements assumed present in solution. ** a c = .13,.11 at 1550°C and 1650°C and a A = .23,.l9. reactions 4.6 and 4.9 to occur. The temperature of 1600°C has been adopted as a reasonable average temperature in the l i q u i d f i l m on the electrode and in the pool during VAR melting. To ensure that a s h i f t in temperature does not change the relationship, reactions 4.5, 4.6, 4.8, and 4.9 were evaluated at 1550 and 1650°C. The results of t h i s evaluation are given in Figure 13. The figure shows that an increase in temperature w i l l increase the driving force of reaction 4.8. However, the driving forces for reactions 4.6 and 4.9 are s t i l l higher at a l l temperatures. From th i s simple thermodynamic discussion i t appears that two reactions are most l i k e l y to occur during VAR melting. These are: 1550 34 TEMP., °C 1600 1650 Figure 13 - Evaluation of the thermodynamic driving force, CaS(s) + 1/3A1 20 3(1, in C xA y) = CaO(l, in C xA y) + [S] + 2/3[Al] 1/3A1 20 3(1, in C xA y) + [C] = 2/3[Al] + CO(g) 4.2 Electron Beam Remelting The electron beam remelting experiments served to show in a qu a l i t a t i v e manner the effect of vacuum remelting on calcium containing inclusions. During remelting, inclusions could be observed both on the electrode t i p and on the pool surface. These inclusions started coalescing on the electrode and formed "beads" of inclusions on the pool surface. The beads had a tendency to float to the 35 edges of the ingot, where they would freeze to the s o l i d s h e l l . Figure 14 shows an inclusion bead which was c o l l e c t e d from the surface of a frozen .ingot. As the figure shows, both the calcium aluminate and the calcium sulphide inclusions f l o a t out together. However, the amount of calcium sulphide in the bead was smaller than expected. Microprobe and SEM-EDX analysis show that the oxide phase in the coalesced beads contains more calcium oxide than the calcium aluminates in the electrode s t e e l , as can be seen in Figure 15. These observations together with the thermodynamic discussion indicate that reactions 4.6 and/or 4.9 possibly take place during remelting. Both reactions give enrichment of calcium oxide in the oxide phase but only 4.6 explains the small amounts of calcium sulphide which remains in the coalesced beads. Metallographic analysis of sectioned electrodes confirm that the inclusions coalesce during remelting. Figure 16 shows the e a r l i e r molten f i l m on an electrode t i p containing an example of coalesced inclusions. 4 . 3 Industrial VAR Samples The results of the chemical bulk analysis of the i n d u s t r i a l electrode and ingot samples are given in Table 4. In this table i t i s interesting to note that regardless of the electrode content of calcium, the ingot w i l l contain only between 5 and 10 ppm. Another interesting observation i s that the loss of sulphur is generally less than 10 ppm. 36 F i g u r e 14 - "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 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 and the bul k phase i s C x A y . (The bead has been g l u e d t o the s u b s t r a t e . ) SEM image x28. INCLUSION • A . Mg Co B E A D Ca ENERGY F i g u r e 15 - X-ray spectrums 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 c o r r e s p o n d i n g i n c l u s i o n "bead". 37 Figure 16 - Coalesced inclusions on an electrode t i p . Light microscope and SEM X-ray images. 38 T a b l e 4 - S u m m a r y o f a n a l y s i s . V x m a r k e d s a m p l e s d e n o t e s e l e c t r o d e s t e e l s , a n d V x R m a r k e d s a m p l e s a r e c o r r e s p o n d i n g • r e m e l t e d i n g o t s . T o t a l c o n t e n t i n C o n t e n t i n S t e e l s t e e l (w t%) a l u m i n a t e (w t%) C a / A l C a A l 0 S C a A l V1 . 0 0 2 9 . 0 3 0 . 0 0 6 6 . 0 0 5 0 . 0 0 1 4 . 0 1 3 . 1 6 V 1 R . 0 0 0 6 . 0 1 7 . 0 0 2 2 . 0 0 1 5 . 0 0 0 3 . 0 0 2 4 . 0 8 V 2 . 0 0 6 3 . 0 3 0 . 0 0 6 8 . 0 0 6 . 0 0 2 5 . 0 0 8 . 2 6 V 2 R . 0 0 0 5 . 0 2 4 . 0 0 1 4 . 0 0 5 2 . 0 0 0 2 . 0 0 4 2 . 1 0 V 3 . 0 0 6 0 . 0 2 6 . 0 0 6 0 . 0 0 7 0 . 0 0 1 8 . 0 1 1 . 2 0 V 3 R . 0 0 0 7 . 0 2 2 . 0 0 2 1 . 0 0 6 0 . 0 0 0 4 . 0 1 0 . 1 3 V 4 . 0 0 6 2 . 0 5 3 . 0 0 6 9 . 0 0 3 7 . 0 0 3 5 . 0 2 7 . 3 8 V 4 R . 0 0 0 6 . 0 3 4 . 0 0 1 4 . 0 0 3 1 . 0 0 0 5 . 0 0 6 4 . 2 5 V 5 . 0 0 3 0 . 0 2 3 . 0 0 5 4 . 0 0 1 5 . 0 0 1 5 _ . 1 8 V 5 R . 0 0 0 8 . 0 2 1 . 0 0 1 6 . 0 0 1 2 . 0 0 0 1 - . 0 5 V 6 . 0 0 2 0 . 0 2 4 • . 0 0 3 2 . 0 0 2 3 . 0 0 1 1 . 0 0 3 5 . 2 6 V 6 R . 0 0 0 2 . 0 2 4 . 0 0 2 5 . 0 0 2 1 . 0 0 0 3 . 0 1 1 . 0 2 * B a s e d o n C a / O b a l a n c e f o r t i i e a l u m i n a t e s . T a b l e 5 s h o w s t h e l o s s o f t h e e l e m e n t s o f i n t e r e s t d u r i n g V A R m e l t i n g . T h e p r e d i c t e d l o s s o f a l u m i n i u m , o x y g e n a n d s u l p h u r w a s c a l c u l a t e d a s s u m i n g t h a t a l l c a l c i u m i s b o u n d a s e i t h e r o x i d e o r s u l p h i d e i n t h e e l e c t r o d e a n d t h a t t h e s o l e r e m o v a l m e c h a n i s m o f i n c l u s i o n s i s r e j e c t i o n t o a f r e e s u r f a c e . T h e p r e d i c t i o n w a s f u r t h e r b a s e d o n t h e l o s s o f c a l c i u m i n t h e o x i d e p h a s e , t h e k n o w n c o m p o s i t i o n o f t h e c a l c i u m a l u m i n a t e s a n d t h e d i s t r i b u t i o n o f c a l c i u m b e t w e e n s u l p h i d e a n d o x i d e i n t h e e l e c t r o d e a n d t h e i n g o t . A s c a n b e s e e n , t h e p r e d i c t e d l o s s o f o x y g e n a g r e e s w e l l w i t h t h e a c t u a l o x y g e n l o s s . On t h e o t h e r h a n d , t h e a n a l y s e d l o s s o f a l u m i n i u m i s e r r a t i c a s c o m p a r e d t o t h e p r e d i c t e d a l u m i n i u m l o s s . T h i s i s p r o b a b l y d u e t o 39 Table 5 - Results of mass balances Steels Atom% lost during remelting Predicted loss* Ca Al 0 S Al 0 S VI : In i n c l . Total .0016 .0033 .022 .027 .013 .0062 .010 .017 .001 7 V2: In i n c l . Total .0032 .0081 .007 .012 .019 .0019 .012 .022 .0049 V3: In i n c l . Total .0021 .0074 .002 .008 .014 .0020 .010 .018 .0053 V4: In i n c l . Total .0034 .0073 .043 .040 .019 .001 1 .009 .017 .0039 V5: In i n c l . Total .0020 .0031 .002 .013 .0003 .011 .018 .001 1 V6: In i n c l . Total .0011 .0025 .0 .002 .0003 .004 .007 .0006 *Assumption: The inclusions f l o a t out. The mass balance i s based on calcium lo s s . interference from aluminium n i t r i d e s . F i r s t l y , the aluminium n i t r i d e s would follow a similar removal pattern during remelting as the oxides, and secondly the aluminium n i t r i d e s are resistant to bromine-methanol d i s s o l u t i o n 6 1 . However, i t appears that rejection to a free surface i s the major mechanism of removal of calcium aluminates. The predicted loss of sulphur i s , except in one case, three times higher than the actual loss. Evidently, some other mechanism takes part in the removal of calcium from sulphide while the sulphur remains in the s t e e l . Consideration of the thermodynamic calculations and the EB experiments suggests that the l i k e l y additional removal mechanism i s that of reaction 4.6: 40 CaS(s) + 1/3A1 20 3(1, in C xA y) = CaO(l, in C xA y) + [S] + 2/3[AL] This agrees well with the fact that calcium i s removed while sulphur remains in the s t e e l . To summarize, the calcium aluminates are removed by rejection to a free surface. One t h i r d of the calcium sulphide is also removed by reje c t i o n . The remainder reacts according to equilibrium 4.6 to form calcium 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 by rejection, and the sulphur w i l l form manganese sulphide, i r o n - sulphide or chromium sulphide during s o l i d i f i c a t i o n depending on the steel composition. Reaction 4.9 could contribute to the increase of CaO in the oxide phase during remelting. However, i t does not account for the loss of calcium while sulphur remains in the s t e e l . This fact, in addition to l i t e r a t u r e data 9, suggests that reaction 4.9 is inhi b i t e d or slowed down, while rection 4.6 occurs more readi l y . 4•4 General Observations Related To Calcium Treated Steels During the course of thi s work some observations were made which are not d i r e c t l y connected to vacuum remelting but to calcium in st e e l in general. These observations w i l l now be discussed. 41 4.4.1 Calcium Aluminate Composition As discussed in the l i t e r a t u r e review, (section 2 . 3 . 1 . ) i t has been suggested that the calcium aluminate composition i s dependent on calcium and sulphur content at constant aluminium content according to Figure 7. However, in th i s work i t was found that the electrode steels, with an oxygen content of 60 — 70 ppm, but only 50 ppm sulphur, y i e l d the graph given in Figure 17. Considering that the steels of H i l t y and F a r e l l contain 50 ppm sulphur and 30 ppm oxygen and for the other graph 150 ppm sulphur and 43 ppm oxygen i t appears that the oxygen content influences the composition of the aluminates more than INFLUENCE OF Ca IN STEEL ON COMPOSITION OF CALCIUM ALUMINATES 12Ca07AI203 CaO Al203 CaO-2AI203 Ca0-6AI203 0 10 20 30 40 50 60 70 80 90 100 CALCIUM CONTENT OF STEEL . ppm. Figure 17 - Composition of calcium aluminates as a function of steel calcium content. Experimental re s u l t s , and results from H i l t y & F a r e l l 2 1 and H a i d a 2 2 *marked steels have lower oxygen contents than the other steels 42 the sulphur content. Probably the resulting aluminate composition w i l l be dependent not only on sulphur and calcium content but also on aluminium and oxygen content. This r e l a t i v e l y complex subject can only be resolved after further invest igat ion. 4.4.2 Inclusions In The Liquid Steel During the investigation i t was observed that metallographic sections taken from small ladle samples contained pure CaS in rims around the aluminates and pure MnS type I I I . On the other hand, samples from large ingots revealed CaS rims containing some MnS and pure MnS type III. This suggests that the s o l i d solution (Ca,Mn)S only develops i f the MnS' i s given enough time to form during s o l i d i f i c a t i o n (see also the phase diagram, Figure 8). The presence of pure MnS could be explained i f a l l calcium reacts with either oxygen or sulphur in the bath. No investigation of the inclusions in a calcium treated l i q u i d s t e e l has been published. Therefore, a calcium containing steel was prepared in the induction furnace and pin samples taken from the l i q u i d . An inclusion from one of the pin samples i s shown in Figure 18. As the pin samples s o l i d i f y immediately when they are drawn from the bath, the 20 nm inclusion c l e a r l y existed in the l i q u i d s t e e l . The sulphide i s pure CaS although the steel contained roughly 1% weight Mn. It is interesting that the CaS i s present as "islands" in the aluminate, and not as a peripheral rim as expected in a normally s o l i d i f i e d s t e e l . 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 s t e e l . 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 . 44 Although the evidence i s scanty, a possible p r e c i p i t a t i o n sequence for the sulphides can be suggested. In the l i q u i d bath calcium sulphide prec i p i t a t e s in or on the calcium aluminates. As s o l i d i f i c a t i o n of the steel proceeds, Mn w i l l segregate and reach such a l e v e l that MnS start p r e c i p i t a t i n g . The MnS can either form a s o l i d solution with e x i s t i n g s o l i d CaS or form individual MnS type III sulphides. If a l l calcium in solution has already reacted with either oxygen or sulphur no calcium w i l l be l e f t to form high content manganese (Mn,Ca)S. This w i l l happen i f the t o t a l steel content of calcium is smaller than 2.5 times the t o t a l content of sulphur in weight percent, since approximately half the calcium i s bound as sulphide. The hypothesis i s supported by the thermodynamic data, as seen in the following reaction, where K i s calculated at 1600°C: CaS + [Mn] = MnS + [Ca] K = 5.2 x 10" 1° It appears unlikely that the equilibrium can be approached at high MnS a c t i v i t y , while low MnS a c t i v i t y and corresponding high CaS a c t i v i t y could lead to equilibrium conditions. In an i n d u s t r i a l s t e e l , i t i s therefore not surprising that no high content manganese (Mn,Ca)S inclusions 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 solution hardening of MnS inclusions (see Figure 9) can thus not be expected, unless very high contents of calcium are present. 45 V. CONCLUSIONS The conclusions of thi s investigation are: 1) The p r i n c i p a l mechanism of removal of calcium aluminates during VAR remelting i s rejection to a free surface. The aluminates are hence c o l l e c t e d on the periphery of the ingot. 2) Approximately one t h i r d of the calcium sulphide i s removed together with the aluminates by rejection to a free surface. 3) Two thirds of the calcium sulphide reacts to form calcium oxide according to the the following reaction: CaS(s) + 1/3Al 20 3(in C xA y) = CaO(in C xA y) + 2/3[Al] + [S], with the calcium oxide being rejected with the o r i g i n a l oxide phases, and the sulphur reacting with available sulphide formers, for instance Mn, during ingot s o l i d i f i c a t i o n . 4) The content of calcium in the remelted ingot w i l l be 5 - 1 0 ppm regardless of the electrode calcium content. Therefore, the calcium treatment i s more important for desulphurization than for inclusion shape contr o l . 46 The results of t h i s study are not in agreement with previous work which attempts to establish the composition of the calcium aluminates as a function of the steel content of sulphur, aluminium and calcium. S p e c i f i c a l l y i t is found that the influence of oxygen content has not previously been s u f f i c i e n t l y taken into account. 47 BIBLIOGRAPHY L.E.K. Holappa: Int.Met.Rev., 1982, v. 27, no 2, pp. 53-76. J.W. Robison: Scaninject I I I , Lulea, June 1983, paper 35. T. Ototani: Ibid, paper 36. P. Dewsnap: I and SM, Aug 1982, pp 15-17. K. Krone, J. Kruger, H. Winterhager: "Beitrag zum Schmelzen von NiCr - Basislegierungen im Hochvakuum."Forschungsberichte des Landes Nordrhein - Westfahlen, nr 1825, Westdeutscher Verlag, Koln und Opladen, 1967. V.I. Kazakov, A. Ya. Golubev, B.V. Sokolov, V.A. Boyarshinov: Metal Science and Heat Treatment, v. 18, Jan-Feb 1976, pp 35-39. M. Wahlster, H. Spitzer: Stahl Eisen, v. 92, Sep 1972, nr 20, pp 961-972. A. M i t c h e l l : Electroslag and Vacuum Arc Remelting Processes. To be published. D. Ya. Povolotskii, R.I. Grechin, A.V. Rechkalova, Yu. V. Kofman, V.E. Roshchin: Steel USSR, Dec 1973, v. 3, nr 12, pp 1004-1007. S. S c h i l l e r , H. Forster, G. Jasch: Metallurgia, Nov 1980, v. 47, nr 11, pp 554-569. C. Doenecke: "Einfluss des Elektronenstrahl-schmelzens auf die chemishen Veranderungen und die mechanischer Eigenschaften hoschfester Baustahle." PhD. thesis, Technischen Universitat Clausthal, 1971. P. Loevenstein: Powder Metallurgy Superalloy Aerospace Materials for the 1980's, v. 1, Switz., 18-20 nov. 1980, pp 1-28. W.H. Sutton: Proc. 7th Int. Conf. Vacuum. Met., 1982, Tokyo, Japan, pp 916-923. F.B. Pickering: "Inclusions", The i n s t i t u t i o n of Metallugists, Monograph nr 3, London, 1979. R. K i e s s l i n g : "Non metallic inclusions in s t e e l " , 2nd ed, The metals society, London, 1978. H. Nordberg (ed i t o r ) : "Swedish symposium on Non-Metallic 48 Inclusions in Steel" Uddeholms AB, Sweden 1981. 17. T.J. Baker, J.A. Charles: JISI, sep 1972, pp702-706. 18. H. Takada, I. Bessho, T. Ito: Trans. IS'IJ, v. 18, 1978, pp 564-573. 19. H. Fredriksson, M. H i l l e r t : Scand. J. Met., v. 2, 1973, pp 125-145. 20. W.J.M Salter, F.B Pickering: JISI, July 1967, v. 207, pp 992-1002. 21. D.C. H i l t y , J.W. F a r e l l : I and SM, v. 2, 1975, Part I: May pp 17-22, Part II: June pp 20-27. 22. O. Haida, T. Emi, K. Sanbongi, T. S h i r a i s h i , A. Fujiwara: Tetsu-to-Hagane, 1980, v. 66, no 3, pp 48-56. 23. G.M. Faulring, S. Ramalingam: Met. Trans. B, v. 11B, 1980, pp 125-130. 24. B.S. Hemmingway: J. Phys. Chem. 1982, v. 86, pp 2802- 2803. 25. C. Leung: PhD thesis 1977, The University of Michigan. 26. R. Ki e s s l i n g , C. Westman: JISI, July 1970, pp 699-700. 27. G. Eklund: Jernkontorets Annaler, v. 154, 1970, pp 321- 324. 28. 0. Kubaschevski, C.B. Alcock: "Metallugical thermochemistry", 5 ed, Pergamon Press 1979. 29. D.R. S t u l l , H. Prophet e t . a l . : JANAF Thermochemical Tables, 2nd ed, and supplements: J. Phys. Chem. Ref. Data v. 3-11,1974-1982. 30. E. Schurmann, R. Schmidt: Arch. Eisenhuttenwes. v. 46, nr 12, 1975. 31. D.L. Sponseller, R.A F l i n n : Trans. Met. Soc. AIME, 1964, v. 230, pp 876-888. 32. S. Kobayashi, Y. Omori, K. Sanbongi: Trans. ISIJ, v. 11, 1971, pp 260-269. 33. S. Gustafsson, P.O. Mellberg: Scand J. Met. v. 9, 1980, pp 111-116. 34. S. Gustafsson, Y. L i : Supplement IV in "On the Transformation of Inclusions when adding strong Deoxidizers": Dissertation by S. Gustafsson. 49 35. T. Ototani, Y. Kataura, T. Degawa: Trans ISIJ, v. 16, 1976, pp 275-282. 36. M. Joyant, C. G a t e l l i e r : "Determination experimentale de la s o l u b i l i t e de CaO dans l ' a c i e r l i q u i d e a 1600°C" IRSID report, 1983. 37. 0. Haida, T. Emi, K Sanbongi, T. S h i r a i s h i , A Fujiwara: Tetsu-to-Hagane, 1978, v. 64, pp 1538-1547. 38. P.O Mellberg, S. Gustafsson: "Thermochemical behaviour of calcium in steel r e f i n i n g " Shanghai symposium on inject i o n metallurgy, Nov 1982. 39. G.K. Sigworth, J.F. E l l i o t t : Metal. S c i . v. 8, 1974, pp 298-310. 40. G.G. Mikhailov, E.P. Baibulenko: Steel USSR, Aug 1981, pp 443-444. 41. K. Sanbongi: Trans ISIJ, v. 19, 1979, pp 1-10. 42. P.T. Carter, T.G. Macfalane: JISI, v. 185, 1957, pp 54- 62". 0 43. R.A. Sharma, F.D. Richardson: JISI, v. 198, 1961, pp. 386-390. 44. R.W. Nurse, J.H. Welch, A.J. Majundar: Trans. B r i t i s h Ceramic S o c , v. 64, 1965, pp 409-418. 45. R.H. Rein, J. Chipman: Trans. AIME, v. 233, 1965, pp 415-425. 46. J. Cameron, T.B. Gibbons, J. Taylor: JISI, v. 204, 1966, pp 1223-1228. 47. G.J.W. Kor, F.D. Richardson, i b i d , v. 206, 1968, pp 700-704. 48. S.X. Dou: J . Phys. Chem, 1981, v. 85, pp 3859-3863. 49. M. A l l i b e r t , C. Ch a t i l l o n , K.T. Jacob, R. Lourtau: J. Am. Ceramic S o c , v. 64, no 5, 1981, pp 307-314. 50. I. E l i e z e r , N. E l i z e r , R.A. Howald, P. Viswanadham: J . Phys. Chem., v. 85, 1981, pp 2835-2838. 51. N. E l i e z e r , R.A. Howald, B.N. Roy: J . Phys. Chem. v. 86, no. 14, 1982, pp 2803-2804. 52. "Handbook of Chemistry and Physics", 53 ed., 1972-1973, Published by the Chemical Rubber Co. 50 53. 0. R e d l i c h , A.T. K i s t e r , C.E. T u r n q u i s t : Chem E n g . P r o g r . Symp. S e r . , 1952, v. 48, n r 2, pp 4 9 - 6 1 . 54. G.H. G e i g e r , D.R. P o i r i e r : " T r a n s p o r t phenomena i n m e t a l l u r g y " , A d d i s o n - W e s l e y P u b l i s h i n g c o , 1973. 55. M. O l e t t e : P r o c . 4 t h I n t . C o n f . Vacuum M e t . , s e c . 1., pp 29-34. 56. E.S. M a c h l i n : T r a n s AIME, v. 218, 1960, pp 314-326. 57. R.G. Ward: J I S I , J a n 1963, pp 11-15. 58. I . L a n g m u i r : P h y s . Rev. v . 2, s e r i e s 2, no 5, 1913, pp 329-3 3 2 . 59. F. R e y e s - C a r m o n a : PhD t h e s i s , UBC 1983. 60. C O . I n g a m e l l s : A n a l . Chim. A c t a . v . 52, 1970, pp. 323-334. 6 1 . I . S . B a s h e i n a , J . B . H e a d r i d g e : A n a l y s t , v . 106, F e b 1981, pp 221-226. 51 APPENDIX A - NOTATION oC = condensation c o e f f i c i e n t Y= a c t i v i t y c o e f f i c i e n t a = a c t i v i t y A = A1 20 3 c = concentration C = CaO C xA y= xCaO-yAl 20 3 f = Henrian a c t i v i t y c o e f f i c i e n t h = Henrian a c t i v i t y H = integral enthalpy of mixing K = equilibrium constant m = evaporated mass M = molecular weight of evaporated species p = vapour pressure p°= vapour pressure of pure element S = evaporation area t = time T = temperature X = atomic fractio n In chemical reactions: [ ] = in metallic solution (s) = s o l i d (1) = l i q u i d (g) = gaseous 52 A P P E N D I X 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 BY A T O M I C A B S O R P T I O N S P E C T R O P H O T O M E T R Y T h i s m e t h o d w a s 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 3 0 6 A t o m i c A b s o r p t i o n S p e c t r o p h o t o m e t e r ( A A S ) . T h e m e t h o d i s a m o d i f i c a t i o n o f t h e p r o c e d u r e d e s c r i b e d b y H i l t y a n d 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 3 o v e r n i g h t p r i o r t o t h e f i n a l r i n s e i n d e - i o n i z e d H 2 0 . T h e n u m b e r o f p i e c e s o f g l a s s w a r e u s e d w a s m i n i m i z e d a n d f i l t r a t i o n p r o c e d u r e s e l i m i n a t e d t o a v o i d c o n t a m i n a t i o n o f t h e s a m p l e s . 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 w a s w e i g h e d a n d t r a n f e r r e d t o a 5 0 m l 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 o f 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 v o l u m e t r i c f l a s k s . S a m p l e s a n d s t a n d a r d s w e r e d i s s o l v e d w i t h 7 m l c o n c e n t r a t e d H N 0 3 a n d 5 d r o p s c o n c e n t r a t e d H C 1 p l u s 1 t o 10 m l H 2 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 s o m e c a s e s c a u t i o u s h e a t i n g o f t h e f l a s k s w a s r e q u i r e d t o d i s s o l v e t h e s a m p l e . T o b o t h s a m p l e s a n d s t a n d a r d s 5 m l o f a l a n t h a n u m c h l o r i d e s o l u t i o n ( 2 9 g L a 2 0 3 + 2 0 0 m l H C 1 d i l u t e d t o 1 0 0 0 m l ) a n d 5 m l o f a p o t a s s i u m s o l u t i o n ( 5 2 g K N 0 3 + 100 m l H N 0 3 d i l u t e d t o 1 0 0 0 m l ) w e r e a d d e d t o c o u n t e r a c t t h e d e p r e s s i n g e f f e c t s o f a l u m i n u m a n d p h o s p h o r u s a n d t o c o u n t e r a c t i o n i z a t i o n i n t e r f e r e n c e . 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 ppm C a , 0 . 0 , 0 . 5 , 1 . 0 , 3 . 0 , a n d 5 . 0 m l w e r e a d d e d t o t h e s t a n d a r d s o l u t i o n s . A l l s o u t i o n s w e r e d i l u t e d t o v o l u m e a n d p a r t i c l e s p r e s e n t a l l o w e d t o s e t t l e o v e r n i g h t b e f o r e a n a l y s i s . T h e A A S a n a l y s i s w a s d o n e a c c o r d i n g t o s t a n d a r d p r o c e d u r e u s i n g a n i t r o u s o x i d e — a c e t y l e n e f l a m e . A P P E N D I X C - S T E E L C O M P O S I T I O N S C o m p o s i t i o n o f E l e c t r o d e S t e e l s ( w e i g h t %) Y_l V 2 V 3 V 4 V 5 V 6 C . 4 1 . 2 4 . 1 7 . 3 1 . 4 2 . 3 9 Mn 1 . 2 0 . 4 6 1 . 0 6 1 . 1 4 1 . 0 8 . 4 0 P . 0 0 9 . 0 1 1 . 0 0 7 . 0 1 0 . 0 0 7 . 0 2 2 S . 0 0 5 0 . 0 0 6 0 . 0 0 7 0 . 0 0 3 7 . 0 0 1 5 . 0 0 2 3 S i . 2 9 . 1 2 . 2 1 . 2 9 1 . 6 8 1 . 0 0 N i 1 . 8 8 2 . 6 4 . 3 6 1 . 81 1 . 8 6 . 3 1 C r . 8 5 1 . 44 2 . 1 9 . 8 4 . 9 4 5 . 0 2 Mo . 2 5 . 5 7 . 9 4 . 4 8 . 4 0 1 . 2 5 V . 0 1 . 1 0 . 0 1 . 0 7 . 0 8 . 9 2 C u . 0 7 . 1 8 . 1 9 . 1 8 . 1 8 - A l . 0 3 0 . 0 3 0 . 0 2 6 . 0 5 3 . 0 2 3 . 0 2 4 C o - . 0 5 . 0 2 . 0 3 . 0 3 - C a . 0 0 2 9 . 0 0 6 3 . 0 0 6 0 . 0 0 6 2 . 0 0 3 0 . 0 0 2 0 0 . 0 0 6 6 . 0 0 6 8 . 0 0 6 0 . 0 0 6 9 . 0 0 5 4 . 0 0 3 2 C o m p o s i t i o n o f I n g o t S t e e l s ( w e i g h t %) V 1 R V 2 R V 3 R V 4 R V 5 R V 6 R C - . 2 5 . 1 7 . 3 2 . 4 2 . 3 6 Mn - . 3 1 . 7 0 . 8 3 . 7 8 . 3 1 P - . 0 1 2 . 0 0 6 . 0 0 9 . 0 0 9 . 0 2 2 S . 0 0 1 5 . 0 0 5 2 . 0 0 6 0 . 0 0 3 1 . 0 0 1 2 . 0 0 2 1 S i - . 13 . 2 1 . 2 7 1 . 7 0 1 . 0 0 N i - 2 . 6 9 . 3 6 1 . 7 9 1 . 8 7 . 3 1 C r - 1 . 4 5 2 . 2 0 . 8 3 . 9 5 5 . 0 2 Mo - . 5 9 . 9 5 . 4 8 . 4 1 1 . 2 5 V - . 1 0 < . 01 . 0 7 . 0 8 . 9 2 C u - . 1 7 . 1 7 . 1 6 . 1 7 - A l . 0 1 7 . 0 2 4 . 0 2 2 . 0 3 4 . 0 2 1 . 0 2 4 C o - . 0 5 . 0 2 . 0 3 . 0 3 - C a . 0 0 0 6 . 0 0 0 5 . 0 0 0 7 . 0 0 0 6 . 0 0 0 8 . 0 0 0 2 0 . 0 0 2 2 . 0 0 1 4 . 0 0 2 1 . 0 0 1 4 . 0 0 1 6 . 0 0 2 5 APPENDIX D - UNCERTAINTY OF CHEMICAL ANALYSIS uncertainty of the chemical analysis i s : Oxygen Sulphur Aluminum Calc ium + 5 ppm + 5 ppm +.005 weight % + 3 ppm

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