The relationship between the size of cementite particles and the subgrain size in quenched-and-tempered steels
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Alloy Ni-2 wt pet W Ni-4 wt pct W Ni-5 wt pet W Ni-6 wt pet W Ni-15 wt pet W Ni-25 wt pet W Ni-26.4 wt pet W
Stress Exponent, n
Reference
4.8 -+0.2 4.8 -+0.2 7.2 4.8 -+0.2 4.4 3.9 3.2 - 3.6*
2 2 3 2 3 3 4
*n = 3.2 for T = 1073 to 1223 K; n = 3.6 for T = 1273 K. represents the total stress range used at that temperature. B a s e d o n t h e c r i t e r i o n g i v e n b y E q . [1], t h e p o s i t i o n s of t h e e x p e r i m e n t a l d a t a s u g g e s t t h a t t h e s t r e s s e x p o n e n t , n , in t h e d i l u t e N i - W a l l o y s , up t o N i - 6 wt p e t W i n F i g . 2, w i l l b e c l o s e t o 5, s o t h a t t h e a l l o y s e x h i b i t unambiguous class I behavior; whereas at the higher solute concentrations, n will have intermediate values between 5 and 3 because the testing conditions then span the climb-glide boundary. These conclusions are in e x c e l l e n t a g r e e m e n t w i t h t h e e x p e r i m e n t a l v a l u e s r e p o r t e d f o r n, a s s u m m a r i z e d in T a b l e I.* *It has been suggestedthat the value of n = 7.2 reported for Ni-5 wt pet W is anomalous, and arisesfrom the testing of very large-grainedspecimens in an argon atmosphere.: Furthermore, the present criterion is consistent with the experimental observation, reported for the Ni-26.4 wt p e t W a l l o y , 4 t h a t t h e v a l u e of n i n c r e a s e s f r o m 3.2 f o r t e m p e r a t u r e s i n t h e r a n g e of 1073 to 1223 K to 3.6 a t T = 1273 K, s i n c e a h i g h e r t e s t i n g t e m p e r a t u r e , u n der the same stress conditions, shifts the data more into the class I region. In a r e c e n t a n a l y s i s , O i k a w a a n d K a r a s h i m a s t o o k F e - 6 . 0 4 wt p c t Mo a n d N i - 2 6 . 4 w t p e t W a s t y p i c a l e x a m p l e s of c l a s s II a l l o y s , b a s e d o n e a r l i e r e x p e r i m e n tal evidence. 4,n By performing stress transient dip t e s t s a n d s t r e s s r e l a x a t i o n e x p e r i m e n t s , it w a s c o n cluded that different rate-controlling mechanisms were occurring in each alloy, thereby suggesting that a s t r e s s e x p o n e n t of n ~ 3 w a s n o t a s u f f i c i e n t c r i t e rion to uniquely identify class H behavior. Two points suggest that this conclusion is premature. Firstly, it should be noted that the experimental data for the Ni-W alloy span the climb-glide boundary i n F i g . 2, i n d i c a t i n g t h a t t h i s i s n o t s t r i c t l y a g o o d e x -
The Relationship Between the Size of Cementite Particles and the Subgrain Size in Quenched-and-Tempered Steels L. ANA ANOJ. atrr LA T h e t h e o r y of t h e i n t e r a c t i o n of g r a i n b o u n d a r i e s with second phase particles during grain growth has been developed by Zener 1 and Gladman z and it has been s u c c e s s f u l l y a p p l i e d t o a n u m b e r of s t e e l s . 3 It i s t h e L. ANAND and J. GURLAND are with the Division of Engineering, Brown University, Providence, R.I., 02912. Manuscript submitted September 4, 1974. 92
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