The formation of a protective oxide layer in machining resulphurized free-cutting steels and cast irons

The effect of a protective oxide layer on tool surfaces in machining resulphurized steels and cast irons has been studied. In the case of resulphurized steels a protective layer was formed on TiC-added carbide tools and alumina ceramic tools when cutting steels containing a high level of oxygen and proper contents of aluminium and silicon, and the layer suppressed the wear of these tools. A protective layer was also observed on silicon nitride ceramic tools when turning cast irons containing a high level of oxygen and a proper content of aluminium. The wear of the ceramic tool in cutting FeSi deoxidized resulphurized steels was serious, and in some cases the crater depth of the tool became larger than that of the carbide tool.