Hot workability of nickel-containing alloys after reheating using sulfur-containing fuel
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The effects of fuel s u l f u r on the hot w o r k a b i l i t y of s e v e r a l n i c k e l - c o n t a i n i n g alloys have b e e n explored in static e x p o s u r e s and in hot r o l l i n g t r i a l s following r e h e a t i n g in S - b e a r ing c o m b u s t i o n a t m o s p h e r e s . Using t h e r m o c h e m i c a l c a l c u l a t i o n s , it is shown that the locus of oxidation and s u l f i d a t i o n p o t e n t i a l s of such g a s e s over p r a c t i c a l a i r - f u e l r a t i o s can be made to coincide for a v a r i e t y of h y d r o c a r b o n fuels, and p r o p a n e doped with H2S has b e e n used as a fuel to s i m u l a t e e n v i r o n m e n t s r e s u l t i n g f r o m f i r i n g d i s t i l l a t e and r e s i d u a l oils. N i c k e l - b a s e a l l o y s containing c h r o m i u m a r e not affected by the p r e s e n c e of s u l f u r s p e c i e s , and w o r k a b i l i t y is independent of r e h e a t i n g conditions at fuel s u l f u r l e v e l s of up to 2 wt pct. S t a i n l e s s s t e e l s may f o r m solid s u b s c a l e s u l f i d e s u n d e r a i r deficient heating, but t h e r e is no effect under lean f i r i n g conditions; b i l l e t w o r k a b i l i t y is not i n f l u e n c e d by s u l f u r . Nickel and n i c k e l - c o p p e r a l l o y s f o r m liquid s u l f i d e s d u r i n g a i r deficient heating, and v e r y poor w o r k a b i l i t y r e s u l t s . Sulfur is a l s o picked up f r o m the gas, and other p r o p e r t i e s may be affected. The t h e r m o c h e m i c a l p r e d i c t i o n s for the o c c u r r e n c e of these liquid sulfides a g r e e well with o b s e r v a t i o n s . An a t t e m p t has b e e n made to identify safe r e h e a t i n g conditions ( t e m p e r a t u r e and a i r - f u e l ratio) for s e n s i t i v e a l l o y s on the b a s i s of e q u i l i b r i u m c o m b u s t i o n gas c o m p u t a t i o n s .
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the United States the p r e f e r r e d fuel for r e h e a t i n g ingot and b i l l e t for hot working has b e e n low s u l f u r n a t u r a l gas both for n i c k e l b e a r i n g alloys and s t e e l s , but the s e v e r e r e s t r i c t i o n s on n a t u r a l gas use d u r i n g the past two w i n t e r s have caused p r o d u c e r s to cons i d e r a l t e r n a t i v e f u e l s . T h i s t r e n d has b e e n of conc e r n to p r o d u c e r s of n i c k e l and n i c k e l a l l o y s , since such m a t e r i a l s a r e c o n s i d e r e d to be e s p e c i a l l y s e n sitive to s u l f u r in c o m b u s t i o n products which may cause the f o r m a t i o n of liquid nickel r i c h s u l f i d e s . The p o s s i b i l i t y of s u l f u r c o n t a m i n a t i o n , which m a y affect p r o p e r t i e s such as p e r m e a b i l i t y of F e - N i m a g n e t i c alloys or ductility of Ni or N i - C u a l l o y s , has also been troublesome. The s t e e l m a k e r s have g e n e r a l l y b e e n able to conv e r t to l i g h t e r fuel oils such as No. 2 or
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