Tempered martensite embrittlement in Fe-Mo-C and Fe-W-C steel

A study on the phenomenon of tempered martensite embrittlement (TME) has been made in experimental Fe-Mo-C and Fe-W-C steel. Charpy impact testing was conducted to evaluate the impact toughness, sensitive to TME. Retained austenite was observed by an analytical transmission electron microscopy in both steels. Both steels represented TME. TME was correlated with the formation of the interlath cementite, resulting from the decomposition of interlath retained austenite. TME occurred in a limited range of test temperatures where the interlath cementite could act as a source of embrittling cracks. Therefore, both the interlath cementite resulting from the decomposition of the interlath retained austenite, and the level of matrix toughness, enabling the interlath cementite to act as an effective embrittler, are necessary to produce TME.