Mn Heterogeneity and Ductility Improvement Realized by Slow Heating Mn-Partitioned Pearlite

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