Microstructure evolution and tensile behaviour of a cold rolled 8 wt\% Mn medium manganese steel

TL;DR

This study investigates how cold rolling affects the microstructure and tensile properties of a novel medium manganese steel, revealing enhanced strain hardening and microstructural mechanisms that improve its tensile performance.

Contribution

It introduces a new medium manganese steel and demonstrates how cold rolling enhances its microstructure and tensile properties through activated twinning and strain-induced martensite formation.

Findings

Cold rolling increases strain hardening rate without reducing ductility.

Activated twinning provides nucleation sites for martensite during tensile testing.

Microstructural analysis explains the enhanced TRIP effect after cold rolling.

Abstract

A novel medium manganese steel named Novalloy with composition Fe-8.3Mn-3.8Al-1.8Si-0.5C-0.06V-0.05Sn was developed and thermomechanically processed through hot rolling and intercritical annealing. The steel possessed a yield strength of 1 GPa, tensile strength of 1.13 GPa and ductility of 41\%. In order to study the effect of cold rolling after intercritical annealing on subsequent tensile properties, the steel was further cold rolled up to 20\% reduction. After cold rolling, it was observed that the strain hardening rate increased continuously with increasing cold rolling reduction but without a significant drop in ductility during subsequent tensile tests. The microstructural evolution with cold rolling reduction was analysed to understand the mechanisms behind this enhanced TRIP effect. It was found that cold rolling activated additional twinning systems which provided a large number of potent nucleation sites for strain induced martensite to form during subsequent tensile tests.