Tool wear and solid state reactions during machining

Measurements have been made of the wear of diamond tools turning mild steel under a range of carefully specified conditions. High rates of wear are observed owing to graphitization of the diamond. Under certain conditions, this graphitization may proceed at a considerable rate even if there is no appreciable temperature rise at the diamond-steel interface. This result implies that the clean surfaces generated by the machining process have chemical activities different from those of the bulk material. Examples of unusual chemical activity have also been observed when using diamond tools to turn other metals, when using tungsten tools to turn graphite, and copper and nickel tools to turn sulphur. The experiments show that machining, under suitable conditions, offers a precise method of measuring rates of reaction between clean solids and of obtaining information on the relative bond strengths of the surface atoms.