Enhanced strength–ductility synergy of multiphase steels via regulation of austenite decomposition during annealing

摘要

Abstract For modern advanced high-strength steels, metastable retained austenite (RA) is introduced into a multiphase microstructure to achieve better strength–ductility balance through interphase deformation accommodation and the transformation-induced plasticity effect. Examples include the quenching and partitioning (QP) process and the bainite isothermal process, where carbon enrichment in austenite is achieved by implementing isothermal around the martensite start temperature, thus improving the mechanical stability of the RA. In this study, the dissimilation of the initial microstructure of high-Si alloy before isothermal treatment was realized by adjusting the quenching process over an extensive range. The effects of the partitioning process and initial isothermal microstructure on the mechanical behavior of Fe–0.28C–2.52Si–2.62Mn–0.05Nb steel were investigated. The two-step QP steel exhibited a better strength–ductility balance than the one-step steel. The tensile strength of the two-step sample reached 1700 MPa and had a product of tensile strength and total elongation of 26.2 GPa . The results showed that the initial formation of athermal martensite accelerated the subsequent bainite transformation kinetics during partitioning. During isothermal holding, the formation of martensite or (and) bainite contributed to the stability of RA via carbon redistribution. Specimens with stable RA exhibited a lower initial work-hardening rate during deformation. A relatively higher volume fraction of RA leads to a continuous work-hardening behavior, thereby significantly improving the total elongation.