Microstructure development and mechanical properties of quenching and partitioning (Q&P) steel and an incorporation of hot-dipping galvanization during Q&P process

The “quenching and partitioning” (Q&P) process has recently been substantiated to be a unique technological route for the production of high strength steels with significant amounts of retained austenite, and thus to provide better combination of strength and ductility. In this work, intercritically annealed specimens followed by Q&P treatment have been applied to low-carbon steel with chemical composition typical for conventional TRIP-assisted steels. Microstructure of the steel treated by the Q&P process was characterized by means of optical microscope, SEM, TEM and XRD. The study suggests that microstructure is mainly composed of ferrite, lath martensite, martensite-austenite islands, retained austenite and a small amount of bainite formed during partitioning. The fraction of bainite formed during partitioning is proportional to quenching temperature. The mechanical property of specimen treated by the Q&P process exhibits an improved combination of strength and ductility than that of the Q&T process. Two schemes of hot-dipping galvanization processes were designed. The results indicate that both hot-dip galvanizing schemes present a limited reduction in tensile strength and a slight enhancement of ductility. The scheme of galvanizing and partitioning after the quenching progress shows a better combination of strength and ductility.