One-step quenching and partitioning treatment of directly hot rolled low carbon steel

Making cost-effective quenching and partitioning (Q&P) steel with good mechanical performance is attractive to the automotive industry. A low carbon steel was hot rolled, directly quenched, and isothermally partitioned using salt bath treatment. Effects of partitioning temperature and time on the microstructures and properties of the steel were studied. The microstructure consisted of carbide-free bainitic ferrite, polygonal ferrite, and retained austenite. The hot rolling introduced strain energy to the austenite, promoting the formation of ferrite, and enhancing the diffusion of carbon in the subsequent partitioning process with an accompaniment of the growth of ferrite. The ferrite was inferred to not only improve the plasticity of the steel but also make the retained austenite more stable. Steel exhibited excellent mechanical properties with high strength and elongation (>23 GPa·%). This study presents a preliminary approach for economical online Q&P steel production.