The mechanism controlling the crater wear of single phase carbide cutting tool materials in the high speed cutting of steel has been identified. A simple model has been developed to describe the wear process. Cutting tests employing inserts coated with Group IVB and VB carbides show excellent agreement with the relative wear rates predicted from the thermodynamic properties of the tool-work system. Thus, for the first time, quantitative calculation of the relative wear rates of various potential tool materials from thermodynamic data is possible. The technique is believed to have broad application to other tool-work combinations. Implications for future research are discussed.