The effect of carbon and titanium on the hot workability of 25Cr-6Ni stainless steels
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EXPERIMENTAL
PROCEDURE
T h i r t y - p o u n d h e a t s of a 2 5 C r 6 N i s t a i n l e s s s t e e l w e r e vacuum melted using virgin raw materials. Initial d e o x i d a t i o n w a s a c c o m p l i s h e d w i t h a n a d d i t i o n of 0 . 0 5 pct C (as carbon-containing chromium). Experience s h o w e d t h a t t h i s i n i t i a l a m o u n t of c a r b o n i s g e n e r a l l y l o w e r e d to l e s s t h a n 0 . 0 2 p c t a f t e r a c a r b o n b o i l . F o l l o w i n g a f i n a l a d d i t i o n of 0 . 0 5 p c t A1, a s e c o n d a d d i t i o n of c a r b o n - c o n t a i n i n g c h r o m i u m w a s m a d e to p r o duce the desired carbon content. Nitrogen was maint a i n e d a t a low l e v e l of a b o u t 0 . 0 0 6 p c t . T h e c h e m i c a l c o m p o s i t i o n s of t h e h e a t s a r e l i s t e d in T a b l e I. Each heat was cast into a 4 in.-square ingot which w a s t h e n h e a t e d to 2 2 0 0 ~ soaked for 1 h and then hot 1 r o l l e d f i r s t t o 3 i n . - s q u a r e a n d t h e n to -~ i n . p l a t e o r t o 1 i n . p l a t e , w i t h o u t r e h e a t i n g in e i t h e r c a s e . One-half in. reductions were taken per pass. The 5 1 i n . p l a t e w a s s u b s e q u e n t l y r o l l e d to ~- i n . p l a t e f r o m a t e m p e r a t u r e of 1 7 0 0 ~ To determine the structure which existed in the alloys a t t h e i n i t i a l h o t w o r k i n g t e m p e r a t u r e , 0.25 i n . t h i c k samples were annealed at 2200~ and immediately water quenched. They were then examined using optical and electron microscopy. In a l l c a s e s , t h e s p e c i H. F. MERRICK and R. C. GIBSON are associated with the International Nickel Co., Inc., Paul D. Merica Research Laboratory, Suffern, N . Y . H . W . HAYDEN, formerly with the International Nickel Co., Paul D. Merica Research Laboratory, is now with the Martin Marietta Co., Research Institute for Advanced Studies, Baltimore, Md. Manuscript submitted August 3, 1970. METALLURGICAL TRANSACTIONS
m e n s w e r e e t c h e d e l e c t r o l y t i c a l l y in a 10 p c t a q u e o u s oxalic acid solution. The parlodion surface replica technique was used for electron microscopy. Identification of precipitates was made by electron diffraction on extraction replicas. R E S U L T S A N D DISCUSSION 1
P h o t o g r a p h s of p l a t e s h o t r o l l e d to ~- i n . t h i c k starting at 2200~ are shown along with their carbon c o n t e n t s in F i g . 1. It c a n b e s e e n t h a t i n c r e a s i n g l y s e v e r e e d g e c r a c k i n g h a s o c c u r r e d i n p l a t e s of t h e f o u r h i g h e s t c a r b o n c o n t e n t s (0.038 to 0 . 0 6 3 p c t ) . A l t h o u g h it i s d i f f i c u l t to s p e c i f y a n e x a e t c a r b o n c o n tent at which the tendency for edge cracking begins, a l e v e l of 0 . 0 3 p c t s e e m s r e a s o n a b l e . Fig. 2 shows a n e x a m p l e of e d g e c r a c k s i n p l a t e f r o m t h e 0 . 0 3 8 p c t C alloy. The cracks occur along the ferrite-austenite i n
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