The effect of rolling and subsequent aging on microstructures and tensile properties of a Fe–Mn–Al–C austenitic steel

Highlights: • Rolling causes large κ formed in dislocation-tangled areas and ultrafine κ in matrix. • The size and number of the large κ are reduced with increasing rolling reduction. • Rolling reduction at 20–60% improves the yield strengths by 600–1100 MPa. • Aging at 550 °C for 2 h further increases the strength of rolled steels by ~200 MPa. The influence of rolling and subsequent aging on the microstructures and tensile properties of an austenitic Fe–23.38Mn–6.86Al–1.43C–0.038Nb–0.29Mo steel was systematically investigated. After hot rolling, the average grain size decreases; the microstructures are heterogeneous due to coarse grains surrounded by fine grains together with the formation of three-types of sub-micron particles along the grain boundaries. Additionally, nanosized κ-carbides consist of large ones mainly located in the vicinity of tangled dislocations and ultra-fine ones evenly distributed in the matrix. Consequently, the strength is significantly increased after rolling. With increasing the rolling reduction from 20% to 60%, the strength gradually increases but ductility decreases primarily due to an increased dislocation density. Meanwhile, the size and number of the relatively large κ-carbides are reduced and the distribution of κ-carbides is gradually homogenized, which affect the strain hardening rate. After subsequent aging at 550 °C, intra-granular κ-carbides are coarsened, leading to an increase in the strength and a decrease in the ductility. The well balance between the κ-carbides precipitation and the dislocation recovery contributes to the optimized tensile properties after rolling at a reduction of 40% and subsequent aging at 450 °C.