Microstructure and Mechanical Properties of High Martensite Content Dual Phase Steel with Different Process of Intercritical Quenching

The effect of quenching time and temperature on the microstructure and mechanical properties of high martensite content dual phase steel was studied by scanning electron microscope, optical microscope, rockwell hardness tester and tensile testing machine. The results show that when the quenching temperature was 785℃, with the increase of holding time, martensite in the quenching microstructure increased and ferrite decreased, while carbide particles reduced and solution diffusion took place. The hardness, yield strength and tensile strength of the test steel increased, and the elongation and area reduction decreased. When the quenching temperature was 785-830℃ and holding for 30 min, with the increase of quenching temperature, ferrite in the quenching microstructure decreased, however, martensite increased. When the quenching temperature was 815℃, the quenching microstructure almost indicated martensite. The hardness and tensile strength of the test steel increased, and the elongation and area reduction decreased. The yield strength increased first and then declined slightly.