Three distinct grinding mechanisms have been found to occur when 304 L stainless steel is ground by alumina wheels. The first results in the grits becoming worn by attritious wear and occurs when temperatures in the grinding zone are relatively high, the second occurs at lower grinding temperatures and results in isolated, tiny areas of workpiece material adhering to grits while the third becomes manifest at relatively low grinding temperatures and results in areas of the wheel, large in comparison to the size of a grit, being covered by adherent workpiece material. Previous proposals advanced to explain metal build-up on the grinding wheel are shown to be inadequate and the phenomenon of large-scale metal transfer to the grinding wheel is shown to be related to the ductility of the workpiece along with the degree of protection conferred by the oxide of the workpiece material. This explanation is confirmed by grinding experiments performed on a series of oxide-resistant workpieces ground in air and, in particular, by the grinding of mild steel in an argon atmosphere under which conditions large-scale transfer of workpiece material to the wheel occurred.