Abstract: 22MnB5 hot-dip galvanized hot stamped steel was heated to different austenitizing temperatures for different time for hot stamping. The effect of austenitizing process for hot stamping on the microstructure and cracks of the galvanized layer on hot stamped steel was investigated through characterization of the microstructure, surface oxides and cracking of the galvanized layer by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) analysis. The results indicate that the galvanized layer is primarily composed of α-Fe (Zn) and a small amount of brittle Fe₃Zn₁₀ after austenitizing. With an increase in heating temperature from 870 ℃ to 890 ℃, the galvanized layer thickness reaches the maximum, and there is a noticeable decrease in the presence of Fe₃Zn₁₀, leading to a reduction of cracks after hot stamping. However, the galvanized layer thickness slightly decreases at 910 ℃ due to Zn volatilization, resulting in the formation of a large amount of Mn, Zn and other elemental oxides on the surface, and the content of Fe₃Zn₁₀ in the galvanized layer significantly increases, leading to a large number of cracks after hot stamping. When the holding time at 890 ℃ is extended from 370 s to 400 s, the Fe-Zn reaction is promoted, more α-Fe(Zn) phases are formed, resulting in an increase of the galvanized layer thickness, but with no significant change of the surface oxidation degree.

Key words: 22MnB5 hot stamped steel, galvanized layer, austenitizing, microstructure, crack