Characterisation of pit geometry in cold-rolled stainless steel strip

Three-dimensional profilometry measurements of the surface roughness on industrially cold-rolled stainless steel samples are used to identify individual pits on the samples. The changes in key pit geometry parameters are extracted from these measurements. As the pits are gradually eliminated through the pass schedule, the ‘characteristic’ pit diameter, spacing and depth fall sharply, while the pit slope rises, from a value of about 15° up to 50°. The contribution of various pit sizes to the pit area is explored. A regime map is constructed for the measured pit sample statistics to indicate the effects of lubricant entrainment at the inlet to the bite or micro-plastic hydrodynamic lubrication of the pits inside the bite.