Performance of CrN radical nitrided tools on deep drawing of advanced high strength steel

The performance of CrN film coating to reduce adhesion in the forming process of advanced high strength steel (AHSS) sheets was investigated. Radical nitriding prior to CrN film coating was used to increase the bond strength between the thin film coating and the tool steel substrate. Electron probe microanalysis was used to characterize nitride diffusion into the tool steel. Scratch testing was carried out to evaluate the bond strength between film coatings (CrN, TiN radical nitride and CrN radical nitride) and the substrate. Ball-on-disk testing was carried out to determine the friction coefficient. Deep drawing experiments with non-coated and coated tools were performed on SPFC 980Y steel sheets. JIS-SKD11 tool steel and TiN-coated tools exhibited high friction under dry sliding with SPFC 980Y sheet material. Moreover, severe adhesion was observed in deep drawing experiments using these mating materials. CrN film showed no adhesion to SPFC 980Y sheet material. The bond strength between a CrN film and the substrate can be increased by a nitride layer before coating.

Research Highlights
► CrN coated tool is effective in reducing adhesion on forming SPFC 980Y materials.
► A high friction seems to be correlated to severe adhesion between mating surfaces.
► The CrN coating film found to be effective in controlling galling on AHSS.
► Radical nitride prior to coating increased the bond strength to the substrate.