Microstructure evolution of Al-Si coating on hot stamping steel during austenitizing

doi:10.13251/j.issn.0254-6051.2021.11.039

Abstract

Abstract: Microstructure evolution of Al-Si coating during austenitization process on the 22MnB5 hot stamping steel was studied by means of differential scanning calorimeter, field emission electron probe and laser confocal microscope. The results show that during the heating process of the coated plate, the Al-Si coating melts at about 570 ℃. Due to the lower temperature, the diffusion of Al, Fe, and Si atoms is blocked by Fe₂SiAl₇. When the temperature rises to about 610 ℃, the diffusion of Al atoms into the coating increases, which makes Fe₂Al₅ further grow; Si atoms diffuse to the outer surface of the coating and the substrate. Because Fe₂Al₅ has a weak ability to dissolve Si atoms, a layer is formed at the Fe₂Al₅ grain boundary in which precipitate is FeSiAl₂, and the remaining Si atoms diffuse on the surface of the coating to form Fe₂SiAl₇. At 750 ℃, Al atoms diffuse into the matrix to form Fe₃Al; the increase of Fe atoms in the coating makes Fe₂Al₅ and FeAl₂ continue to grow; due to the lower solubility of Si atoms in the Fe₂Al₅ and FeAl₂ phases, Fe₃SiAl₅ precipitates will form at the grain boundaries. Compared with Fe₂Al₅, Fe₃SiAl₅, Fe₃Al, the growth rate of FeAl₂ phase is faster, and it occupies the largest volume of Al-Si coating. This is because of FeAl₂ orthorhombic crystals, the high vacancy rate (30%) along the c-axis in the grid leads to stronger growth kinetics of the FeAl₂ phase.

Key words: differential scanning calorimeter, Al-Si coating, intermetallic compound, hot stamping steel

CLC Number:

TG14

Wang Junhui, Cui Qingling, Zeng Linlin, Gao Xinyu, Liang Jiawei. Microstructure evolution of Al-Si coating on hot stamping steel during austenitizing[J]. Heat Treatment of Metals, 2021, 46(11): 220-225.

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