Effect of Partial Austenitization Treatment on Microstructure and Mechanical Properties for Multiphase Steels

Abstract

In this study, the microstructural evolution and mechanical properties of a 0.15 pct C-2.09 pct Mn multiphase steel was investigated. To produce a multiphase microstructure, a newly developed two-step processing of partial austenitization and quenching (PAQ) treatment was used. In the first step, the steel with initial martensitic microstructure was partially austenitized at 690 degrees C for 8 hours. After cold rolling, a rapid reheating to 840 degrees C and quenching done to simulate hot dip galvanizing conditions. To better understand the PAQ process, thermodynamic and kinetic simulations using ThermoCalc and DICTRA predicted phase transformations and elemental partitioning. Microstructural characterization via LM, SEM, and EBSD revealed an ultrafine-grained multiphase structure consisting of bainite, M/A, and intercritical ferrite. The PAQ840 sample showed an ultimate tensile strength of 740 MPa and excellent ductility with 20 pct total elongation.