Design of a novel Mn-based 1 GPa duplex stainless TRIP steel with 60% ductility by a reduction of austenite stability

We report on the microstructure, texture and deformation mechanisms of a novel ductile lean duplex stainless steel (Fe-19.9Cr-0.42Ni-0.16N-4.79Mn-0.11C-0.46Cu-0.35Si, wt.%). The austenite is stabilized by Mn, C, and N (instead of Ni). The microstructure is characterized by electron channeling contrast imaging (ECCI) for dislocation mapping and electron backscattering diffraction (EBSD) for texture and phase mapping. The material has 1 GPa ultimate tensile strength and an elongation to fracture of above 60%. The mechanical behavior is interpreted in terms of the strength of both the starting phases, austenite and ferrite, and the amount, dispersion, and transformation kinetics of the mechanically induced martensite (TRIP effect). Transformation proceeds from austenite to hexagonal martensite to near cubic martensite (gamma -> epsilon -> alpha'). The epsilon-martensite forms in the austenite with an orientation relationship close to Shoji-Nishiyama. The alpha'-martensite nucleates at the intersections of deformation bands, especially epsilon-bands, with Kurdjumov-Sachs and Nishiyama-Wassermann relationships. The ferrite deforms by dislocation slip and contains cell substructures. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.