Impact of Al and Mn Addition on Microstructure and Mechanical Properties of Lightweight Stainless Steel

The effects of Al and Mn on the microstructure and mechanical properties of Fe–12Cr–5Ni–0.4C–(6,10)Mn–(0,2,4)Al (wt%) lightweight stainless steels are investigated. The results indicate that the as‐referred 6Mn0Al and 6Mn2Al steels exhibit a fully austenitic microstructure. An increase in Al content results in ≈6% and 2% ferrite in the 6Mn4Al and 10Mn4Al steels, respectively, accompanied by refined austenite grains and an increase in yield strength. Deformation‐induced α′‐martensitic transformation (DIMT) and mechanical twinning are the dominant deformation mechanisms in 6Mn0Al steel, leading to a high work‐hardening rate and a tensile strength of 863 MPa. The increased stacking fault energy due to higher Al content in 6Mn2Al steel suppresses DIMT, making mechanical twinning the primary deformation mechanism. The total elongation of 6Mn2Al steel reaches 77%, significantly higher than the 61% measured in 6Mn0Al steel. Additionally, the deformation mechanisms of 6Mn4Al and 10Mn4Al steels are dominated by mechanical twinning. The pre‐existing ferrite leads to an increased work‐hardening rate but reduced ductility, with total elongation decreasing to 56% and 50% for 6Mn4Al and 10Mn4Al steels, respectively. The lower elongation of 10Mn4Al steel compared to 6Mn4Al steel corresponds to a decreased work‐hardening rate, as mechanical twinning is suppressed by the higher Mn content.