Multiphase precipitation and its strengthening mechanism in a V-containing austenite-based low density steel

Abstract

Multiple precipitates have been utilized so as to improve the strength and strain hardening rate of austenite-based low density steel. Thus, a two-step heat treatment process including annealing and aging was designed for a V-containing Fe–20Mn–9Al-1.2C steel. Based on the analysis of microstructures and mechanical properties under different heat treatment processes, the precipitation behavior and strengthening mechanism were investigated. After annealing at 900 °C and aging at 550 °C, the microstructure of the steel consists of austenite matrix with V4C3 particles, κ-carbides and ferrite with DO3 particles. It is found that the steel exhibits an ultimate tensile strength (UTS) of 1339 MPa and specific strength (SS) of 199.3 MPa cm3/g. High strength and strain hardening ability result from the synthetic effect of shearing and Orowan mechanisms from multiple types of precipitates. Despite the low hardening ability, κ-carbides with shearing mechanism could enhance the yield strength significantly. Meanwhile, Orowan type V4C3 particles effectively improves the strain hardening rate as well as the strength. Fine planar slip bands with dispersive dislocation localization contribute to the strengthening of the steel.