Tempered martensite embrittlement: Role of retained austenite and cementite

H. K. D. H. Bhadeshia and D. V. Edmonds


The microstructural and property changes accompanying the tempering of quenched low-alloy steels ahve been examined and correlated with the tempered martensite embrittlement (TME) phenomenon. TME was detected in an Fe-C-Mo steel and found to be controlled by the relatively coarser intralath cementite, rather than by the interlath cementite resulting from the decomposition of <2% retained austenite present as films between the martensite laths. In an Fe-C-V steel containing about 5% intralath retained austenite, TME was controlled by coarsening of the comparatively larger amount of interlath cementite resulting from thermal decomposition of the interlath retained austenite. In both cases fracture was translath, consistent with the crack nucleation role of cementite rather than that of providing an easy fracture path. In an Fe-C-Mn-Si steel containing negligible retained austenite and fine carbides TME was not found. Furthermore, embrittlement could not be associated with the transition from epsilon-carbide to cementite.

Metal Science, Vol. 13, 1979, pp. 325-334.

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