Microcracking in plate martensite of AISI 52100 steel
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AH/n =
n=
kJ~lneo l
f~lne l
AH = AH, ev
gY
0.23 -+0.01
k l rSln?: 1 eY
1.82 + 0.02
0.42 +-0.02
0.43 + 0.05
t h a t t h e v a c a n c y a n n e a l i n g k i n e t i c s in a l u m i n u m i s e n hanced by magnesium addition and a mobile vacancymagnesium complex is proposed. Taking a vacancym a g n e s i u m b i n d i n g e n e r g y ~v of 0.2 e v a n d a v a c a n c y m i g r a t i o n e n e r g y '8 in a l u m i n u m of 0 . 6 5 e v , t h e m i g r a t i o n e n e r g y of s u c h a c o m p l e x i s ~ 0 . 4 5 e v . T h e r e f o r e , t h e o b s e r v e d v a l u e of ~ 0 . 4 2 e v , f o r t h e a c t i v a t i o n e n ergy associated with the serrated yielding, appears to b e in g o o d a g r e e m e n t w i t h a v a c a n c y - m a g n e s i u m complex migration energy. 1. K. Mukherjee, C. D'Antonia, R. Maciag, and G. Fischer: J. Appl. Phys., 1968, vol. 39, p. 5434. 2. A. Portevin and F. LeChatelier:Compt. Rend., 1923, vol. 176, p. 507. 3. A. W. McReynolds:Metals Trans., 1949, vol. 185, p. 32. 4. V. A. Phillips, A. J. Swain, and R. Eborall: J. Inst. Metals, 1952-53, vol. 81, p. 625. 5. S. G. Harris: Vacancies and Other Point Defects in Metals and Alloys, p. 220, Institute of Metals, London, 1958. 6. J. Caisso: Rev. Met., 1959, vol. LV1, p. 237. 7. J. Caisso and J. Guillot: Rev. Met., 1962, vol. L1X, p. 395. 8. D. J. Bailey, W. F. Flanagan, and G. E. Miller: Acta Met., 1965, vol. 13, p. 436. 9. A. T. Thomas: ActaMet., 1966, vol. 14, p. 1363. 10. H. Borchers, H. M. Tensi, and H. Ehrhardt: Z. Metallk., 1967, vol. 58, p. 863. 11. B. J. Brindley and P. J. Worthington: Acta Met., 1969, vol. 17, p. 1357. 12. A. H. Cottrell: Phil. Mag., 1953, vol. 44, p. 829. 13. K. Mukherjee, C. D'Antonio, and R. J. Maciag: ScriptaMet., 1970, vol. 4, p. 209. 14. S. R. Ramaswami and S. R. MacEwen:Bull. AIME, 1967, vol. 2, p. 4. 15. J. Takamura, K. Okazaki, and I. G. Greenfield: J. Phys. Soc. Japan, 1963, vol. 18, p. 78. 16. T. Kino, S. Kabemoto, and S. Yoshica: J. Phys. Soc. Japan, 1963, vol. 18, p. 85. 17. A. J. Perry: ActaMet., 1966, vol. 14, p. 1143. 18. A. C. Damask and G. J. Dienes:Point Defects in Metals, Gordon and Breach Science Publishers, Inc., New York, 1963.
s u l t d i r e c t l y f r o m t h e i m p i n g e m e n t of l a r g e p l a t e s of martensite. The variables affecting microcracking h a v e r e c e n t l y b e e n s t u d i e d , 9 a n d it h a s b e e n s h o w n t h a t microcracking sensitivity is directly related to carbon content and is not influenced by grain size, retained a u s t e n i t e , q u e n c h i n g m e d i u m , o r s e v e r i t y of t h e q u e n c h .
According to Grange, I~ microcracking in AISI 52100 steel is a surface phenomenon that usually does not exist in the interior of a quenched high-carbon martensite specimen. He explains the formation of microcracks as being due to the relief of microstresses in untempered or low-tempered martensite when a free surface is created upon microscopic examination. Upon high-temperature tempering, Grange did not find microcracking in t
