Tensile deformation of a low density Fe–27Mn–12Al–0.8C duplex steel in association with ordered phases at ambient temperature

Abstract

Room temperature tensile behavior of a low density Fe–27Mn–12Al–0.8C duplex steel was correlated with both undeformed and deformed microstructures, focusing on the effects of the ordered phases on plastic deformation. Various ordered phases were formed by quenching of the steel after annealing at the (austenite+ferrite) two phase region. The B2 domains bounded by swirled thermal antiphase boundaries were formed in disordered ferrite matrix. In addition to the B2 domains, fine D03 phases were evenly distributed through both B2 domains and disordered ferrite matrix. The nano-sized κ carbides were precipitated in austenite. The steel exhibited the relatively high yield strength and the low strain hardening rate initially, leading to the moderate elongation. The specific strength of the steel reached ~146MPacm3/g. Deformed structure of ferrite is manifested by short, straight segments of paired dislocations (superdislocations) with narrow mechanical antiphase boundaries. In austenite, a single planar dislocation glide was dominant at low strains and multiple planar slip occurred at high strains. Based on these microstructural observations, it is suggested that strain hardening of the steel is dominated mainly by shearing of the ordered phases by superdislocations (in ferrite) and planar gliding dislocations (in austenite). In addition, the tensile deformation behavior of the present duplex steel was compared with that of other low density Fe3Mn3Al3C duplex steels.