Influence of surface modification on galling resistance of DC53 tool steel against galvanized advanced high strength steel sheet

The presence of galling is always detrimental when sheet metal forming advanced high strength steel (AHSS). Galling tends to reduce tool life, degrade the quality of components, and increase scrap rate of production. To prevent or postpone the initiation of galling and thereby extend the service life of DC53 tool steel forming tools, surface modification techniques like nitriding treatment and thermal diffusion (TD) carbide treatment can be utilized. A custom-designed sheet strip tribo-tester that includes bending deformation was used to perform tribological tests on tool steels having surface treatments. Comparisons were made of the friction coefficient, surface roughness and critical total sliding distance of individually treated and conventionally quenched/tempered DC53 tool steel dies against galvanized DP600 sheet. The initiation and evolution of galling and other wear mechanisms were subsequently analyzed and compared. Results indicated significant improvement in galling resistance for dies with surface modification. The improvement in galling resistance for the nitrided and TD coated DC53 tool steels, respectively, was attributed mainly to (i) the constitution of complex Fe₃N, Fe₄N phases in compound layer, and (ii) the good anti-adhesive capability of VC coating with high hardness in TD layer.