Hot stamped parts with desirable properties in medium Mn TRIP steels

Abstract

Abstract With the increasing requirements of the automotive industry for reduced weight and safety improvement, high strength steel hot stamping parts have been increasingly applied in the automotive industry. But the process is along with higher equipment requirements and tool wear because of the high temperature.In this study, warm tensile deformation behavior of 6Mn, 6MnNb and 6MnNbMo steels was investigated, in conjunction with warm stamping to understand the role of Mn and Mo and evaluate the mechanical properties of Ushaped parts.The results show that the hotstamped6MnNbMo Ushaped parts at both 700 ° C and 760 ° C exhibited the desirable mechanical properties, e.g. the SDB (Strength Ductility Balance) values reached 23.6-36.8 GPa·%, which were more than double or triple times higher than those of hotstamped boron steels. The work hardening rate increased with addition of Nb and Mo, while it decreased with flow stress.As the stamping temperature decreased from 760 to 700 ° C, the fractions of soft phase ferrite and retained austenite increased, resulting in the enhanced elongation with reducing tensile strength from 1600-1814 MPa to 1361-1467 MPa.The combined addition of Nb and Mo raised UTS with a slight decrease in El, and improved the distribution uniformity of mechanical properties, which is of great importance when applying medium Mn steels to the automotive structural components for ensuring safety of passengers.