Influence of carbides on the high-temperature tempered martensite embrittlement of martensitic heat-resistant steels

The high-temperature temper embrittlement of martensitic heat-resistant 10Cr12Ni steel was studied. The results demonstrate that there is some irreversible temper embrittlement when the steel is tempered at 625 °C. The irreversible temper embrittlement can be overcome by re-tempering at higher temperature. The tempered martensite embrittlement at 625 °C is attributed to the precipitation of M23C6-type carbides along the martensite lath and prior austenite grain boundaries. The tempering process can be divided into three stages: In the first stage, the martensite laths recover and M7C3-type carbides precipitate inside the martensite laths, leading to the improvement of the toughness. In the second stage, M7C3-type carbides dissolve, and M23C6-type carbides precipitate along the martensite laths and prior austenite grain boundaries. The M23C6-type carbides play a nucleating role in the development of cracks, leading to tempered martensite embrittlement. In the third stage, the toughness gradually recovers with the further recovery of the martensite laths.