Effects of the composition, shape factor and area fraction of sulfide inclusions on the machinability of re-sulfurized free-machining steel

The effects of the composition, shape factor (length:width ratio) and area fraction of sulfide inclusions on the machinability of re-sulfurized free-cutting steels have been investigated in terms of cutting force, flank wear and surface roughness. The cutting force was reduced by sulfide inclusions in the following decreasing order: MnS, (Mn,Ca)S, MnS-RE₂S₃ and (Mn,Ca)S-RE₂S₃. Flank wear of the cutting tools was also reduced by sulfide inclusions in the same increasing order as above. The elongated sulfide inclusions were more effective in reducing the cutting force than the globular sulfide inclusions, whilst the latter were more effective in reducing the flank wear of the tools. The increase of area fraction of sulfide inclusions resulted in reduction of both the cutting force and the flank wear of the tools. There were two conflicting factors concerning the effects of both the shape factor and area fraction of sulfide inclusions on the surface finish of the steel workpieces.