Effect of cooling rates and compressive deformation of austenite on bainitic transformation and microstructure for plastic die AISI P20 steel

Abstract

In order to reduce both manufacturing process and manufacturing cost, a thermomechanical process for plastic die AISI P20 steel has been developed. The P20 steel treated by the thermomechanical process can be used to manufacture plastic dies directly without any subsequent heat treatments. In the present work, the dependence of microstructure upon cooling rate and deformation condition has been investigated for P20 steel with the aim of optimizing the thermomechanical process. The results show that the hardness decreases and eventually reaches a plateau, meanwhile the microstructure changes from sheaf-like bainite to granular bainite with decreasing the cooling rate in both of the recrystallized and unrecrystallized austenite. Austenite deformed at 850°C exhibited mechanical stabilization against sheaf like bainite transformation during continuous cooling, resulting in the microstructure refinement and higher hardness in P20 steel.