Anti-galling Performance of Two Hot Stamping Mould Steels
SUN Qiang1,2, HUANG Suqi1,2, CAI Zhuwen1,2, DANG Weidong1,2, WU Xiaochun1,2
1 School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China 2 State Key Laboratory of Advanced Special Steel, Shanghai 200444, China
Abstract: Hot stamping is a metal-forming process for stamping and forming high-strength steel plates, which can not only greatly improve the forming performance of the material, but also refine the grain size through high-temperature phase transformation. However, during the hot stamping process, the high-strength steel sheet has been heated above the austenitizing temperature. At this time, the yield strength of the high-strength steel sheet is low, and the high-strength steel sheet can easily be scratched by the debris knob. The mechanical properties of high strength steel plates were reduced significantly. In this respect, many auto parts manufacturers have relieved the hot-stamping galling problem of parts by surface treatment, but this treatment will increase production costs. For this reason, this study starts from the alloying ratio of the mould materials, and through experimental and theoretical research, it is preliminarily judged that the anti-galling performance of hot stamping moulds is related to the ability of plastic deformation resistance of the mould materials. In order to verify the conjecture, the transmission electron microscope (TEM), X-ray diffractometer, residual stress meter, micro Vickers hardness tester were used to observe the carbide types, carbide distribution, dislocation density in the two tempered materials (SDCM steel and SDHS2 steel), and residual stress gradient and micro Vickers hardness gra-dient of the section after shot peening. The results show that compared with SDHS2 steel, the yield strength of SDCM steel with better anti-galling performance is higher, which makes it have stronger resistance to plastic deformation under the same applied stress, making its deformation softening layer shallower. In addition, vanadium-based carbides are predominant in both SDCM steel and SDHS2 steel after heat treatment. Among them, SDCM steel with higher carbon content, higher vanadium content and lower chromium content contains higher carbide volume fraction and dislocation density, which results in higher precipitation strengthening and dislocation strengthening effect, increasing the yield strength of the material. Therefore, under the same applied stress, SDCM steel has excellent plastic deformation resistance.
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2021, Vol. 35 
