Numerical prediction of microstructure and mechanical properties for the S-rail with tailored properties

Abstract

Hot stamped parts are applied widely to reduce the weight and meet safety requirements for new vehicles. It has been noticed, however, that hot stamped parts of fully martensitic transformation lead to a low elongation of about 5%. Hot stamped parts may be enhanced by locally tailoring their mechanical properties to improve their energy absorption. And partially heated dies offer a method for decreasing the cooling rate of blank located in hot region to obtain the hot stamped parts with tailored properties. In this paper, an S-Rail die was separated into three sections. The middle part of the die was heated and other parts maintained room temperature during the hot stamping process. The blank of 22MnB5 boron steel was stamped by this S-Rail die. A numerical model was established to simulate the stamping process. The microstructure and mechanical properties of blank located in the hot region and cold region were investigated. At the hot region temperature of 500°, the variation of Vickers hardness through the S-Rail bottom and side wall was investigated. The austenite decomposition curves in hot region and cold region were also given to reveal the difference of phase transformations.