High strength and plasticity of AISI 430 ferritic stainless steel achieved by a recrystallization annealing before quenching and partitioning process

Abstract AISI 430 ferritic stainless steels treated by traditional bell furnace annealing exhibit good plasticity but low strength, which limits its application range. A new heat treatment process, a recrystallization annealing and quenching and partitioning (Q&P) process, was applied to AISI 430 ferritic stainless steel in this study. This type of process enabled AISI 430 ferritic stainless steel to have high strength while maintaining good plasticity. AISI 430 ferritic stainless steel can be used as a material for automobile body structures, and its application range has been greatly expanded. The Q&P860×5 sample had the best comprehensive performance: its strength was 730 MPa, its elongation after break was 19.4%, and its product of strength and elongation was 14.2 GPa%. After treatment by the Q&P process, the microstructure was composed of ferrite, martensite, and retained austenite. The fraction of each phase was determined, and it was observed that the fraction of retained austenite gradually increased as the recrystallization annealing temperature and time increased. M23C6 precipitates formed in both the martensite and retained austenite, and a large number of low-angle grain boundaries were also observed. The texture of the Q&P samples mainly comprised γ-texture and weak α-texture. Compared with the recrystallization annealing samples, the tensile strength of the Q&P samples was greatly improved, while the high degree of plasticity was maintained, and the yield plateau disappeared.