The effect of carbide precipitation on the properties of ausrolled hardenable stainless steel
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Heat Effect
Kcal/g-mole
Btu/lb.
SenszbleHeat Heat of Fusion Heat of Solution Total
126 (-+5) +47 (-+5) -10 (-+5) 163 (-+9)
706 263 -56 913
The Effect of Carbide Precipitation on the Properties of Ausrolled Hardenable Stainless Steel
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Hecltmg Somplr Size 59 5 mg Reference o~.-AI203
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J O H N H. HOKE
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6. G. Derge:Basic Open Hearth Steelmaking, 3rd ed, p. 820, A.1.M.E.,NewYork, 1964. 7. P. D. Garn: ThermoanalytzcalMethods of Investigation, 1st ed., pp 180-92, AcademicPress, New York, 1965. 8. N. A. Langeand G. M. Forker: Handbookof Chemistry, 10th ed., p. 1586, McGraw.Hill,NewYork, 1961.
I 250
1 300
I 350
Reference tempcralur~
I 400
I 450
I 500
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Fig. 1--Differential thermal curve for colemanite (25 pct in t~-A1203). b o r a t e , has the c o m p o s i t i o n CazBeOu 9 5H20. s Due to the l a r g e a m o u n t of w a t e r of h y d r a t io n p r e s e n t , it was felt that a p r e l i m i n a r y r o a s t i n g o p e r a t i o n m i g h t be n e c e s s a r y . A c c o r d i n g to M a c K e n z i e , s d e h y d r a t i o n b e gins suddenly at 338~ and f i n i s h e s a b r u p t l y at 419~ h o w e v e r , no value f o r the heat of d e h y d r a t i o n is a v a i l a b l e . Using values f r o m the l i t e r a t u r e f o r the heat c a p a c i t y and heat of fusion of c o l e m a n i t e , 4 e s t i m a t i n g the heat of solution in the s l a g u s in g the data of K u l i k o v , 5 and i g n o r i n g f o r the t i m e being the heat of d e h y d r a t i o n of c o l e m a n i t e , the a m o u n t of heat to r a i s e 1 gm o l e of the a n h y d r o u s c a l c i u m b o r a t e f r o m a m b i e n t c o n d i t i o n s to solution in the s l a g at 1500~ was d e t e r m i n e d as shown in T a b l e I. Us i n g the value f o r the heat r e q u i r e m e n t to r a i s e s c r a p f r o m a m b i e n t c o n d i t i o n s to liquid at 1800~ 6 of 568 Btu p e r lb., the s c r a p r e p l a c e m e n t v a l u e of c o l e m a n i t e is 1.61 (+0.09) lb. of s c r a p p e r lb. of c o l e m a n i t e . T h e heat of d e h y d r a t i o n was d e t e r m i n e d e x p e r i m e n t a l l y u s i n g a DTA a p p a r a t u s . A t y p i c a l DTA t r a c e f o r c o l e m a n i t e is shown in F i g . 1. The heat effect w as e s t i m a t e d by the m e t h o d of c o m p a r a t i v e a r e a s ,7 u s i n g the d e h y d r a t i o n of c a l c i u m o x a l a t e m o n o h y d r a t e as a s t a n d a r d , 8 a s 21 (+5) k c a l p e r g - m o l e which i n c r e a s e d the s c r a p r e p l a c e m e n t v a l u e to 1.77 (+0.09) lb. of s c r a p p e r lb. of c o l e m a n i t e . T h i s i n c r e a s e is s m a l l and p r e r o a s t i n g of c o l e m a n ire d o e s not a p p e a r to be n e c e s s a r y for t h e r m a l reasons. 1. Ind. Min., 1970, vol. 38, p. 34. 2. C. J. Lewisand R. S. Bruski: Aust.Patent C32195, 1968. 3. R. C. Mackenzie:TheDifferential Thermallnvestigation of Clays, 1st ed., p. 373, MineralogicalSoczety(ClayMineralsGroup), London, 1
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