It is well established that diamond is an inefficient abrasive for grinding ferrous materials especially the low carbon variety. The widely held view is that as ordinary carbon has a strong affinity for iron forming iron carbide (Fe3C) this should also be the case with diamond (cubic carbon) when grinding steel. The high rate at which diamond grinding wheels wear down when grinding low carbon steel is said to be a consequence of this action. We suggest here another mechanism evidence of which is provided by scanning electron micrographic (SEM) data.