Carbon partitioning from Mn-depleted lath martensite to Mn-enriched austenite during slow cooling

The high-temperature austenite inherits the Mn heterogeneous distribution from Mn-partitioned pearlite, leading to the formation of alternative Mn-enriched austenite and Mn-depleted martensite during cooling to room temperature. Here, we further demonstrate that the carbon partitioning from Mn-depleted martensite to Mn-enriched austenite is realized by slow cooling (air cooling) from austenitization to room temperature, which is probably assisted by the Mn-enrichment in austenite. As a result, the fraction of retained austenite is significantly increased compared to that of water cooling, leading to an increase in uniform elongation by 60 % while maintaining 2000 MPa tensile strength.