Multiple deformation mechanisms of quenching-austenite reversion-treated medium-Mn steel containing various precipitates

초록

We systematically investigated the annealing-temperature-dependent microstructures and mechanical properties of quenching–austenite reversion-treated medium-Mn steel containing various precipitates. The reverse transformation from martensite (α′) to austenite (γ) via diffusion of γ stabilizers (Mn, Ni, C) into γ resulted in a microstructure consisting of lath-shaped γ and tempered α′ in samples annealed at 620 (A620) and 680 °C (A680). Fine γ particles, likely nucleated at dislocations and precipitate interfaces, were observed within α′. A high density of B2 precipitates was present within the tempered α′ in both samples. VC precipitates were also observed within γ and tempered α′ grains, as well as at γ/tempered α′ interfaces in both A620 and A680. Tensile tests revealed excellent strain hardening in both samples, originating from dislocation multiplication and the activation of deformation twinning, ε, and α′ deformation-induced martensitic transformation (DIMT) in γ. The higher initial strain hardening rate of A620 (ε < 0.05) was primarily attributed to its greater HDI strengthening. At higher strains (ε > 0.05), stronger DIMT in A680 enhanced strain hardening through combined TRIP effect and HDI strengthening, resulting in similar overall strain hardening behavior in both samples. Despite differences in microstructure and DIMT kinetics, A620 and A680 exhibited comparable strength–ductility combinations, highlighting the synergistic role of microstructure, precipitates, multiple plasticity-enhancing mechanisms, and HDI strengthening in guiding the design of precipitate-strengthened quenching–austenite reversion-treated steels. © 2024

키워드