Accelerated Transformation of Hot Deformed Austenite in SCM435 Steel

Abstract

The element chromium and molybdenum delays the γ→α phase transition, while the deformation energy storage and high temperature diffusion can promote the γ→α phase transition process. The phase change of alloy structural steel SCM435 under different deformation temperature and cooling path after heating and holding at 1050°C was measured by a thermal simulator. The microstructure and hardness of the steel under various rolling processes were studied by using SEM and micro-hardness tests. The low deformation temperature (800~720°C) and the slow post-rolling cooling speed (1~0.3°C/s) were favorable for the γ→α phase change, where the phase microstructure showed the low hardness. As the isothermal temperature decreases, the microstructure changes from Pearlite (P)+ Ferrite (F) to P+ F + Martensite(M). The lower the isothermal temperature, the higher the martensite content in the structure, and the higher the hardness was. Both the low temperature deformation and 660°C isothermal treatment could quickly accelerate the γ→α transformation of SCM435. The fastest transformation temperature in this case for pearlite of SCM435 was 660°C, and the phase transition ended within 300s, which significantly shortened the time compared with the isothermal time in the low temperature zone.