Effect of hot/warm rolling on the microstructures and mechanical properties of medium-Mn steels

This study provides processing strategies for the Fe-0.20C-11.0Mn-4.0Al steel to meet the requirements of different automobile parts by using hot rolling + intercritical hardening + tempering (HR) and warm rolling + tempering (WR). The mechanical properties and microstructure evolution were investigated. Due to a mild transformation-induced plasticity (TRIP) effect, twinning-induced plasticity (TWIP) effect and strain anisotropy during deformation, the HR sample showed the best product of tensile strength and elongation, which was above 70 GPa·% (strength: 889 MPa, total elongation: 79.6%); such a steel can be used in manufacturing complex-shaped automotive components such as anti-collision beams, C pillars and bumpers and even for cold working. The WR sample also achieved excellent mechanical properties, with a product of tensile strength and elongation of 45.8 GPa·% (strength: 1171.5 MPa, total elongation: 39.1%). Furthermore, the WR sample exhibited an increased dislocation density, fresh martensite formation and reduced high temperature ferrite phase, leading to a high yield strength of 938.7 MPa, which can be used in B pillars and floors for the prevention of intrusion in case of car collision.