Effect of prior austenitic grain boundary composition on temper brittleness in a Ni-Cr-Sb steel
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brittled value (de-embrittling). lz In addition to the dec r e a s e in DBTT, d e - e m b r i t t l i n g c a u s e s the mode of b r i t t l e failure to change from i n t e r c r y s t a l l i n e to t r a n s c r y s t a l l i n e cleavage. These c h a r a c t e r i s t i c s suggest that t e m p e r e m b r i t tlement of alloy s t e e l s is r e l a t e d to i m p u r i t y and p o s sibly alloying element s e g r e g a t i o n to p r i o r austenite grain boundaries. In the investigation r e p o r t e d here, t e m p e r b r i t t l e n e s s of an Sb doped N i - C r s t e e l was studied by d e t e r m i n i n g how the composition of the p r i o r austenitic grain boundaries in the alloy changed during heat t r e a t m e n t s designed to produce varying d e g r e e s of e m b r i t t l e m e n t . The ductile b r i t t l e t r a n s i t i o n t e m p e r a t u r e was used to define the d e g r e e of e m b r i t t l e m e n t . MATERIAL The alloy studied was a high purity, Sb doped, N i - C r steel containing 0.4 wt pct C, 1.5 wt pct Cr, 3.5 wt pct Ni, and 0.07 wt pct Sb (heat V-30-B). This alloy was chosen b e c a u s e : 1) E a r l y investigations 9'1~ d e m o n s t r a t e d that So doped, N i - C r s t e e l s a r e highly susceptible to e m b r i t t l e merit. 2) Chemical a n a l y s i s , of thin a r e a s adjacent to the g r a i n b o u n d a r i e s , was p o s s i b l e for Fe, Ni, Cr, and Sb at all l e v e l s of e m b r i t t l e m e n t . The complete a n a l y s i s of s t e e l V-30-B is given in Table I. EXPERIMENTAL METHODS Heat T r e a t m e n t and Mechanical Testing The heat t r e a t m e n t s used were designed to produce both v a r y i n g d e g r e e s of e m b r i t t l e m e n t , c h a r a c t e r i z e d by ductile b r i t t l e t r a n s i t i o n t e m p e r a t u r e s ranging b e tween - 100~ and + 600~ and 100 pct i n t e r c r y s t a l l i n e f r a c t u r e s u r f a c e s , f r o m which the composition of the p r i o r austenitic grain boundaries could be determined. Before e m b r i t t l i n g , all s a m p l e s were subjected to a s t a n d a r d t r e a t m e n t that yielded the nonembrittled conVOLUME 5, JANUARY 1974-279
Table I. Analysis of Steel V-30-B (Wt Pct)
Heat
C
Ni
Cr
Sb
Mn
Si
S
AI
As
P
Sn
B
V-30-B
0.38
3,4
1,5
0.07
0.006
0.05
0.004
0,003
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