Microstructure and Mechanical Properties of Q&P Steel

The heat treatment process of Si-Mn Q&P(quenching and partitioning) steel was experimentally investigated using salt bath furnace.Effects of partitioning time on mechanical properties,microstructure,retained austenite content of the tested steel after heat treatment and carbon content in retained austenite had been studied.It is shown that the microstructure of the tested steel was lath martensite and retained austenite.It was found that retained austenite with thin film type of inter-lath or blocky type was distributed in different positions respectively.Blocky type retained austenite was found along austenitic grain boundaries and the thin film distributed between martensite laths.The retained austenite content and carbon content in retained austenite of the tested steel increased with the increase of partitioning time.The strength and plasticity reached maximum (above 37 300 MPa·%) at the partitioning temperature of 300℃ and the partitioning time of 1 200 s.