The Mn heterogeneity in the medium manganese steel has been realized deliberately using fast heating. However, fast heatingis not easy for industrial production. Here, we counter-intuitively demonstrate that the slow heating not only can retain theMn-heterogeneous distribution from alternative Mn-enriched cementite and Mn-depleted ferrite in the initial pearlite, butalso modify the stability, morphology and fraction of retained austenite (RA). Compared to fast heating, a wider distributionand a lower average content of Mn in film RA are achieved due to the transition of austenite formation from partition localequilibrium to negligible partition local equilibrium. Meanwhile, the slow heating boosts the dissolution of the sphericalcementite, leading to a stronger retention of spherical RA. Consequently, slow heating exhibits a 30% larger ductility owingto a stronger austenite-to-martensite transformation during straining while the strength keeps similar. The present studyindicates that the slow heating opens a new avenue to produce Mn-heterogeneous steels having high strength and ductility.
The Mn heterogeneity in the medium manganese steel has been realized deliberately using fast heating. However, fast heatingis not easy for industrial production. Here, we counter-intuitively demonstrate that the slow heating not only can retain theMn-heterogeneous distribution from alternative Mn-enriched cementite and Mn-depleted ferrite in the initial pearlite, butalso modify the stability, morphology and fraction of retained austenite (RA). Compared to fast heating, a wider distributionand a lower average content of Mn in film RA are achieved due to the transition of austenite formation from partition localequilibrium to negligible partition local equilibrium. Meanwhile, the slow heating boosts the dissolution of the sphericalcementite, leading to a stronger retention of spherical RA. Consequently, slow heating exhibits a 30% larger ductility owingto a stronger austenite-to-martensite transformation during straining while the strength keeps similar. The present studyindicates that the slow heating opens a new avenue to produce Mn-heterogeneous steels having high strength and ductility.