Influence of tool steel surface topography on adhesion and material transfer in stainless steel/tool steel sliding contact

Abstract

Transfer of work material to the tool surface is a common problem in many metal forming and metal working operations, especially in the case of work materials with a high adhesion tendency e.g. stainless steel, aluminum and titanium. In many operations, material transfer occurs already during the initial contact and with time it may result in degradation and roughening of the tool surface which will affect the surface quality of the formed or machined work material surface, e.g. problems related to galling in sheet metal forming. In the present study, the mechanisms behind the initial stages of material transfer between stainless steel and tool steel have been investigated under well controlled laboratory conditions and analyzed using optical surface profilometry and scanning electron microscopy.The results show that, independent of tool surface topography, transfer of stainless steel occurs already after a very short sliding distance. Depending on the tool steel surface topography, initial transfer occurs on two different scales. For a fine polished tool steel surface, fine scale transfer occurs in connection to protruding hard phase particles (carbides and carbonitrides) while for a ground rough surface large scale transfer occurs in connection to grinding scratches, where these act to mechanically scrape off material resulting in lumps off stainless steel on the tool steel surface. Also, sliding perpendicular to the grinding scratches results in more severe material transfer as compared with sliding parallel to the grinding scratches. Finally, the present paper illuminates the usefulness of combining optical surface profilometry and scanning electron microscopy as a powerful analytical tool when it comes to understanding the mechanisms controlling material transfer in a sliding contact on a μm-scale level.