Comparison of Surface Treatments for H10A Tool Steel in Hot Stamping Process

Abstract

Trials were carried out under industrial hot stamping conditions to compare the effect of different surface treatments on hot working tool steel. In comparison to conventionally quench and tempered AISI grade H10A tool steel, a PVD CrN coating and plasma nitride treatment were applied to the H10A tool steel. Following tool failure, the microhardness and the microstructure of the surface of the steel were analysed to determine metallurgical changes of the tool steel by the stamping process. The results in the present study show that the plasma nitrided tool increased die life twofold. This increase in wear life is attributed to the increase in surface hardness which decreased gradually with depth, and the presence of residual compressive stresses within the surface. In comparison, the CrN coating was unable to extend tool life. The failure of the CrN coating was attributed to delamination and microcracking brought about by a combination of residual stresses within the coating. This was due to differences in the coefficient of thermal expansion and fracture of the coating under impact loading.