Structure-property relation in a quenched-partitioned low alloy steel involving bainite transformation

The impact of bainite transformation during initial quenching and partitioning steps on the microstructural evolution was studied in a Fe-0.4C-2.0Mn-1.7Si-0.4Cr (wt%) steel. By optimizing quenching cooling rate and partitioning time, the final microstructure comprised of initial-quenched bainite, carbon-depleted martensite, bainite formed during partitioning, and final-quenched martensite, together with retained austenite. High volume fraction of retained austenite with desired carbon-content was obtained by prolonging the partitioning time to 2700 s The initial-quenched bainite, bainite formed during partitioning, and martensite provided carbon atoms to austenite, leading to the formation of retained austenite with different degree of stability. Consequently, a good combination of strength and elongation (ultimate tensile strength: 1688 MPa, total elongation: 25.2%) was obtained.