Partitioning temperature-dependent microstructures and mechanical properties of precipitation-hardened medium-Mn steel

Abstract

This study reports the partitioning temperature-dependent microstructures and mechanical properties of precipitation-hardened medium Mn steel processed by room-temperature quenching and partitioning. The hot-rolled Fe–7Mn-0.3C–3Ni-1.5Si–1Al–1Cu-0.3V (wt.%) steel was processed by austenitization, water quenching to room-temperature, and partitioning treatment at 200, 300, 400, and 500 °C for 600 s. The samples before and after the partitioning process at temperatures below 400 °C show a microstructure consisting of lath martensite and retained austenite, whereas the sample partitioned at 500 °C shows a notably high fraction of retained austenite, owing to the formation of austenite grains during the partitioning process. The C partitioning during the partitioning process led to higher C contents in the samples processed by austenitization, quenching, and partitioning than in the sample processed by austenitization and quenching. The co-precipitation of VC precipitates and dispersed fine particles could exhibit a precipitation-strengthening effect. The sample partitioned at 200 °C shows an excellent strength-ductility combination, i.e., a yield strength of 740.9 MPa, an ultimate tensile strength of 1623.6 MPa, and a total elongation of 23.8%. Film-like retained austenite stabilized by carbon partitioning could exhibit high mechanical stability, leading to a gradual transformation induced plasticity (TRIP) effect and superior mechanical properties. In contrast, the samples partitioned at temperatures above 400 °C show poor ductility with brittle fracture, which could be related to the formation of martensite/retained austenite (M/A) constituents.

Keywords

• Room-temperature quenching and partitioning
• Medium Mn steel
• Precipitation
• TRIP effect