Effect of isothermal transformation treatment and tempering on the microstructure and hardness of a medium c and high si steels

© 2021 Iron and Steel Institute of Japan. All rights reserved.This research work aims to study the effect of 2wt%Mo on bainitic transformation kinetics and bainite morphology in 0.6wt%C-1.2wt%Si-1.0wt%Mn-0.2wt%Cr steel. Specimens are austenitized at 950°C and rapidly cooled in salt bath and isothermally treated between 200°C-300°C for different time intervals. Another set of specimens are rapidly cooled in oil after an austenitization treatment and then tempered in the temperature range of 200°C-550°C. In C-Mn-Si specimens, the amount of retained austenite increases with increasing the amount of bainite but no retained austenite is observed in bainitic C-Mn-Si-Mo specimens. The tempering behavior of C-Mn-Si-Mo alloy is considerably different than that of the Mo free alloy. Mo in a martensitic microstructure of C-Mn-Si-Mo alloy shows the secondary hardening effect peak upon tempering at 500°C. The examination of the secondary hardening would also contribute to the behavior of Mo in tempered bainitic steels. The bainitic specimens do not show a peak hardness but softening is retarded upon tempering at the same temperature range