Experimental investigation on galling performance of tool steel in stamping of UHSS sheets

Abstract

The objective of this study is to experimentally investigate the effect of surface roughness parameters on the galling performance of tool steel used in the stamping of ultra-high-strength steel (UHSS) sheets. The galling performance of uncoated and TiAlCrN coated AISI D2 tool steel was evaluated against a 1.4 mm-thick dual phase (DP) 980 UHSS sheet, using pin-on-flat surface test. For evaluating the galling performance of tool steel, the surface roughness parameters and topography were tested under three surface conditions: as-received (AS), as-received and post-polished (AS+P), and as-received coating (AS+C), whereas the sheet surface was tested under as-received and no post-treatment surface condition. The variation in the coefficient of friction was monitored as a function of sliding distance. The sliding distance at which severe galling began to occur owing to the transfer of sheet material to the tool surface was determined as the critical sliding distance for a sudden increase in the friction coefficient. Experimental results showed that a plateau-like topography, with low average surface roughness, negative skewness and high kurtosis value, improved the galling performance of tool steel. Additionally, the hard TiAlCrN coating of tool surface also effectively reduced galling tendency.