Abstract: Thermal simulation experiment on DH780 hot-dip galvanized high strength steel containing high Si was carried out. The thermal simulation experiment mainly focused on the slow cooling temperature and fast cooling outlet temperature of the material. In the slow cooling temperature experiment, the slow cooling temperature was set to 740, 720 and 700 ℃, and the rapid cooling outlet temperature was set to 460, 400 and 350 ℃ .The results show that the yield strength of the material increases obviously when the slow cooling temperature is set high, and the tensile strength of the material remains basically unchanged when the slow cooling temperature is set at 740 ℃ or 720 ℃, but the tensile strength decreases slightly when the slow cooling temperature is set to 700 ℃. The main reason is that the decrease of slow cooling temperature leads to the increase of ferrite content and the decrease of fast cooling rate, which leads to the decrease of martensite content in materials. The tensile strength of the material is reduced. In the experiment of rapid cooling outlet temperature, it is found that the strength grade of the material is guaranteed when the rapid cooling outlet temperature is set at 460 ℃, but the elongation value is close to the standard lower limit, and the material strength decreases obviously when the rapid cooling outlet temperature is 400 ℃. It is mainly due to the appearance of bainite in the material, resulting in insufficient martensite content in the material. When the rapid cooling outlet temperature is set at 350 ℃, the material has excellent mechanical properties. There is a small amount of retained austenite in the material, and the martensite is dispersed, and good elongation is obtained so as to ensure the formability of the material.

Key words: hot-dip galvanizing, slow cooling temperature, rapid cooling outlet temperature, martensite, retained austenite