Effect of annealing process on microstructure and properties of 980MPa grade hot-dip galvanized dual-phase steels

Abstract

A hot-dip galvanizing simulator studied the effects of soaking temperature and rapid cooling end temperature on the microstructure and mechanical properties of 980MPa grade hot galvanizing dual-phase steel. The results show that at the end of a rapid cooling temperature of 290°C, with the increase of soaking temperature, the tensile strength of the test steel increases, the yield strength decreases at first and then increases, and the elongation decreases as a whole. The microstructure is composed of ferrite and martensite. At the soaking temperature of 800°C, the strength decreases, and the elongation increases with the increase of the end temperature of rapid cooling. When the end temperature of rapid cooling is lower than 320°C, the martensite tempering is not apparent, and there are many high-density dislocations in the ferrite near the neighbor. When the cooling end temperature is 350°C, some martensites are tempered. The twins in martensite are widened, carbides are unevenly precipitated along the twin planes, and the dislocation density decreases. When the soaking temperature is between 800°C and 820°C, the end temperature of rapid cooling is between 260°C and 290°C. Annealing and zinc plating are beneficial to obtain dual-phase steel with excellent mechanical properties.