Abstract
The literature associates several mechanisms of fracture with tempered martensite embrittlement (TME). With the use of a series of chromium-molybdenum steels containing 0.3–0.5% C and the examination of heats containing nominally 0.002 and 0.02% P at each carbon level, this study has reproduced the transgranular and intergranular brittle modes of TME in 0.4 and 0.5% C steels and revealed a transgranular ductile mode of TME in the 0.3% C steels. Room temperature instrumented Charpy V-notch impact testing was used to detect TME, and together with fractographic characterization by scanning and transmission electron microscopy, showed that the nature of the crack initiation ahead of the notch was a key factor in differentiating the various mechanisms of TME. All of the observations could be explained by consideration of the effects of carbon content and tempering temperature on the carbide distribution and the matrix strain-hardening behavior of the steels. High phosphorus, by virtue of its segregation to retained alloy carbide particles and austenite grain boundaries during austenitizing, lowered impact toughness relative to low phosphorus specimens not just in the TME range but in all tempered conditions. Therefore, phosphorus, although shown to be potent embrittling element in hardened steels, is not responsible for TME.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call