Effects of Heat Treatment on Microstructure and Tensile Properties of a Fe-27Mn-12Al-0.8C Low-Density Steel

Abstract

A low-density duplex steel of Fe-27Mn-12Al-0.8C (density 6.53 g/cm³) was directly quenched to room temperature and ordering treated at 500°C and 700°C after solution treatment. The heat-treated microstructures and corresponding room-temperature tensile properties were investigated. The κ phase precipitated in austenite in all the cases such that its size became coarser with increasing ordering temperature. Ferrite of the as-quenched steel consisted of the B2 domains and disordered ferrite with uniformly distributed nanosized D0₃ particles. Ferrite of the 700°C ordering steel exhibited basically identical features to the as-quenched steel, but with the coarser B2 domains, finer D0₃ particles, and less disordered ferrite. By contrast, the D0₃ domains were mainly observed in ferrite of the 500°C ordering steel. The yield strength of the 500°C ordering steel was higher than other two steels, which showed the similar yield strengths. The elongation of the as-quenched steel was higher than two ordering-treated steels. Deformation of austenite was manifested by the κ phase shearing by planar gliding dislocations. Intensive interactions of superdislocations were mainly observed in ferrite, depending on the type of the ordered phase. Factors influencing the strength and deformation behavior of the low-density duplex steel were discussed based on observation of deformed microstructure. Overall, the high-Mn/Al duplex steels with the ordered phases exhibit the high specific strength, the low density, and the moderate strain hardening that are suitable for the structural use requiring high strength and light weight.