High strength-elongation product of Nb-microalloyed low-carbon steel by a novel quenching–partitioning–tempering process

In this article, a novel quenching–partitioning–tempering (Q–P–T) process was applied to a Fe–0.25C–1.5Mn–1.2Si–1.5Ni–0.05Nb (wt%) hot-rolled steel, and its optimized parameters were obtained by a Gleeble-3500 thermal simulator and salt baths, respectively. Mechanical property results of the as-treated Q–P–T samples show that the Nb-microalloyed low-carbon steels subjected to Q–P–T processes cover a wide spectrum of strength (1200–1500 MPa) and elongation (14–18%), and exhibit excellent product of strength and elongation (21,000–22,000 MPa%). Microstructural characterization indicates that high strength results from dislocation-type martensite laths and dispersively distributed fcc NbC or hcp ɛ-carbides in martensite matrix and good ductility is attributed to transformation induced plasticity (TRIP) effect from plenty of retained austenite flakes between martensite laths.

► As-treated Q–P–T steel covers a wide spectrum of strength and elongation.
► High strength results from martensite laths and NbC or ɛ-carbides in martensite matrix.
► Good ductility is attributed to TRIP effect from retained austenite flakes.
► Si can only suppress the formation of Fe3C in short tempering time steel.
► Si cannot suppress the formation of ɛ-carbides in low tempering temperature.