Effect of double annealing on microstructure and mechanical properties of Mn-TRIP steel

A novel double annealing process was applied to a Mn-TRIP steel. As a result, a great combination of yield strength of 829MPa, tensile strength of 1132MPa and total elongation of 42.1% was obtained. The improvement of mechanical property was contributed to microstructure evolution. By double annealing process, ferrite grains were refined and VC could effectively precipitate instead of cementite, which contributed to the enhancement of yield strength. Austenite fraction was increased and two types of austenite morphology (block and lath) were obtained. In addition, Mn partitioning was promoted, leading to high Mn enrichment in austenite grains. Consequently, the austenite grains with high stability provided continuous and active TRIP effect, contributing to a great work-hardening behavior and increasing strength and ductility.