Research work is carried out on the cutting tool temperature field with adhering layer formation when machining Ca-S free-cutting stainless steel. By means of combining thermocouple measuring method and finite element (FE) analysis, the cutting temperature distributions and their relation with the formation of adhering layer are investigated. The adhering layer, which has a protective effect on cutting tools, is basically composed of a ternary compound oxide similar to the inclusions in the steel. When there is an adhering layer formed during machining, the temperature gradient in the direction vertical to the tool rake face is smaller than that without the layer. The small temperature gradient is favorable for the stable formation of the adhering layer on cutting tools. The stable cutting temperature field keeps the relatively stable adhering layer and influences the layer composition distributions on the tool face. © 1998 Elsevier Science S.A.