Investigation was carried out on the lubrication mechanism of NbC-reinforced tool for hot metal working. Observations on the surface of reinforced tool carried out after use to clarify that the tool surface was covered with a kind of oxide. X-ray analysis showed that the oxide was Nb2O5. Laboratory experiment was carried out to grasp the condition of heating in air for the transformation of NbC to Nb2O5, and following the condition NbC powder was heated to obtain Nb2O5 powder. Hot rolling experiment of steel sheet followed. Prior to rolling Nb2O5 powder was placed on one side of the sheet on the inlet side, and the curl of the rolled sheet was measured. Elastic-plastic FEA was carried out to specify the coefficient of friction at high temperature. The numerical result well matched to the experimental result when the value of coefficient of friction of Nb2O5 was 0.15. The value is equivalent to the value of graphite which is a well know good lubricant at high temperature
