New considerations on tempered martensite embrittlement
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,ffo-Y'dn
v=--g
[14]
or
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where (D--DT-K-)is the average value of (D/K) obtained by averaging over the spherical image (or orientation). Equation [141 relates the volume of a convex body of any arbitrary shape to the average properties of its bonding surface.
REFERENCES 1. H. Minkowaki: Math. Ann., 1903, vol. 57, p. 447. 2. R.T. DeHoff: Quantitative Microscopy, R. T. DeHoff and F. N. Rhines, eds., McGraw-Hill, New York, NY, 1968, pp. 129-47. 3. D.J. Struik: Lectures on Classical Differential Geometry, AddisonWesley Press, Inc., Cambridge, MA, 1950. 4. J. W. Calm and R. L. Fullman: Trans. Met. Soc. AIME, 1956, vol. 206, p. 610. 5. R.T. DeHoff: Trans. Met. Soc. AIME, 1962, vol. 224, p. 474. 6. W. A. Johnson: Metal. Prog., 1946, vol. 49, p. 87. 7. J. Sarra: Image Analysis and Mathematical Morphology, Academic Press, London, 1982. 8. Quantitative Microscopy, R.T. Detloff and F.N. Rhines, eds., McGraw-Hill, New York, NY, 1968, pp. 52-89. 9. R.L. Fullman: Trans. Met. Soc. AIME, 1953, vol. 197, p. 447.
New Considerations on Tempered Martensite Embrittlement HOON KWON and CHONG HEE KIM A loss in toughness after tempering in the temperature range of 250 ~ to 450 ~ in martensitic steels, in spite of a loss in strength, has been referred to as tempered martensite embrittlement (TME). TME has been suggested to be the intergranular brittle fracture which is associated with the combined action of impurities and carbides at the grain boundaries. 1-4The transgranular brittle type of TME, which is correlated with interlath (or intralath) carbides has also been reported. 5'6'v TME has been considered mainly by microstructural aspects. On the other hand, Ronald ~ suggested that TME was associated with the inhibition of plastic flow in the matrix and that the occurrence of intergranular brittle fracture was also a result of the inhibition of plastic flow at the grain boundaries. Recently, Zia-Ebrahimi and K r a u s s 9 considered that TME was correlated with the strain hardening behavior of the matrix in the various tempered conditions with different carbide distribution and that the impurities at the grain boundaries were not responsible for TME. HOON KWON is Assistant Professor, Department of Metallurgical Engineering, Kookmin University, 861-1, Jeongneung-Dong, Seongbuk-Ku, Seoul 132, Korea. CHONG HEE KIM is Professor, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Cheongryang, P.O. Box 131, Seoul 131, Korea. Manuscript submitted July 16, 1985. METALLURGICALTRANSACTIONS A
TME has usually been characterized by a trough in room temperature impact toughness as a function of tempering temperature. However, since the occurrence of TME is dependent upon the test temperature which affects the matrix toughness, it is not always desirable that test temperature be fixed at room temperature for characterization of TME. Kwon and Kim '~ have reported that the transgranular and intergranular brittle types of TME occur in Mo- and W-steels and Ni-steel, respectively, and have
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