Effect of Annealing Processes on Microstructures and Mechanical Properties of Medium Mn Steel

Abstract

Two annealing processes have been designed to process a medium Mn steel, namely, the traditional direct two-phase annealing process and the pre-quenching treatment before two-phase annealing process, called two stage annealing process. The experimental results indicated that different annealing processes resulted in completely different microstructures, and a significant difference in mechanical properties. The microstructures of the steel after direct two-phase annealing process were coarse tempered martensite matrix and retained austenite. In this case, the optimum mechanical properties with total elongation of 29.87 %, tensile strength of 932 MPa and UTS*TE of 27.84 GPa•% were achieved after annealing at 625 °C for 18 h. The annealing process with pre-quenching treatment could realize two kinds of retained austenite, including acicular austenite and blocky austenite. The process with pre-quenching treatment could improve mechanical properties as well as shorten the optimal annealing time. The steel with two stage annealing process achieved optimal mechanical properties after pre-quenching and annealing at 625 °C for 4 h with tensile strength of 1177 MPa, total elongation of 30.92 % and UTS*TE of 36.39 GPa•%.