On the effect of precipitation of (Cr, Fe)7C3 carbides in structural and phase recrystallization of a ledeburitic class cast steel

The paper is devoted to the development of a theory reflecting the change of carbide phase amount and carbon concentration in austenite of high-chromium ledeburitic steels and irons, as well as corresponding behaviour o f hardness of quenched alloys, as a function of quenching temperature. Two variants of heat treatment are considered. In variant A the 1.4 % C - 12 % Cr - 1 % Mo alloy serving as an example was fast cooled after crystallization and had almost completely austenitic structure of the matrix, and on further fast reheating to the quenching temperature took again the same state as after crystallization. In variant B it is accepted that the alloy had the grained pearlite stucture as a result of either austenite decomposition or high-temperature tempering of martensite. On fast heating to the isotherm the alloy undergoes the α→γ transformation, after which the dissolution of carbide particles begins. In calculations the authors used a kinetic theory of precipitation and dissolution of carbide particles developed on the basis of Zener - Hillert concept. For both variants, A and B, the calculations describe rather well the observed hardness change and the effect of decreasing the maximum hardness temperature to 950-1000 °C (variant A) from 1000-1070 °C (variant B).