Enhancing ductility of the TRIP aided bainitic ferrite steel by Mn heterogeneity introduced via reversion: Towards the 3rd generation

A novel approach to enhance the ductility of the transformation-induced plasticity (TRIP)-aided bainitic ferrite (TBF) steel was proposed in this work. Lamellar lath Mn-heterogeneity was introduced into the single austenite grain through austenite-reversion from martensite by slow-heating or intercritical annealing. Acicular austenite is formed accompanied with apparent Mn enrichment occurring during reversion, and such a lamellar lath Mn-inhomogeneity is remained even after full-austenitization. Highly stable retained austenite (RA) is formed at the original Mn-enriched region after austempering with higher Mn and carbon contents than those of traditional austempering from Mn-homogenized austenite. In addition, higher total fraction and larger ratio of film-like RA is obtained in the heterogeneous-austenite than homogeneous one. These contribute to the ductility improvement of the TBF steel. [Display omitted]