On the ferrite and bainite transformation in isothermally deformed 22MnB5 steels

The effect of austenite deformation on ferrite transformation and bainite transformation is reviewed in this paper. In the ferrite zone on continuous cooling transformation (CCT) diagram of 22MnB5 steel, isothermal tensile tests were carried out in various deformation conditions on Gleeble 3800 thermo-mechanical machine, and microstructures were observed. The influence of hot deformation on the driving force of ferrite transformation was theoretically analyzed based on the 22MnB5 steel. The effects of deformation temperature, strain amount, strain rate and cooling rate on the ferrite transformation of the 22MnB5 steel were also investigated. The ferrite transformation of the 22MnB5 is induced by isothermal deformation and the incubation period is significantly shortened. Below the start temperature of bainite transformation (Bs), isothermal tensile tests and microstructure observation were performed. The effects of deformation temperature and strain amount on the bainite transformation of the 22MnB5 steel were investigated. The isothermal deformation below Bs promotes the bainite transformation obviously, while the hot deformation above the Bs promoting the bainite transformation is not observed in the investigated testing conditions.