Influence of Intercritical Quenching Temperature on Microstructure, Mechanical Properties and Corrosion Resistance of Dual-Phase Steel

This work investigated the microstructure, mechanical properties and corrosion behavior of dual-phase (DP) steel after different intercritical quenching treatment and compared the results with commercial AH32 steel. The results indicate that the microstructure of all tested DP steels was composed of lath martensite and polygonal ferrite. As the temperature increased from 750 to 850 °C, the martensite lath became slender, whereas martensite volume fraction (Vm) increased from 53 to 71%. The change in the morphology and content of martensite not only led to an increase in hardness and yield strength, but also to a decrease in the plasticity and impact toughness, which was consistent with the mixture law. However, the ultimate tensile strength did not increase but declined, which was an unusual behavior. It was related to the micro-void coalescence fracture mechanism caused by the ferrite/martensite interface decohesion. Moreover, the increasing temperature led to the enhanced galvanic effect between ferrite and martensite, accelerating the corrosion rate of DP steels in a 3.5% NaCl solution. A comparison of all results in our work indicates that DP750 steel with 53% martensite had excellent comprehensive properties.