Development of pseudoelasticity in Fe-10Ni-7Mn (wt%) high strength martensitic steel by intercritical heat treatment and subsequent ageing

In this research, ternary Fe-10Ni-7Mn (wt%) high strength martensitic steel was subjected to study the reverse transformation of martensite to austenite by intercritical annealing at 600 °C in the ferritic-austenitic (α+γ) dual phase region for various holding times. Subsequent isothermal ageing was performed at 480 °C for 3.6 ks. The experimental results revealed that during intercritical annealing above the heating rate of 5 °C/s, reverse martensite transformation occurs by the diffusionless mechanism. Also, the X-ray diffraction (XRD) and electron back scattering diffraction (EBSD) analyses represented that the volume fraction of the retained austenite at room temperature increases with increasing the holding time up to 7.2 ks and then it gradually decreases. Furthermore, the cyclic tensile test results revealed pseudoelastic behavior of the retained austenite after subsequent ageing. The maximum amount of pseudoelasticity was obtained about 40% at the sixth loading-unloading cycle for the specimen intercritically annealed at 600 °C for 7.2 ks after subsequent isothermal ageing at 480 °C for 3.6 ks.