EFFECTS OF THE COMPOSITION, SHAPE FACTOR AND AREA FRACTION OF SULFIDEINCLUSIONS 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-sulfuri zed free-cutting steels have been investigated in terms of cutting for ce, flank wear and surface roughness. The cutting force was reduced by sulfide inclusions in the following decreasing order: MnS, (Mn,Ca)S, MnS-RE(2)S(3) and (Mn,Ca)S-RE(2)S(3). 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 reduci ng the cutting force than the globular sulfide inclusions, whilst the latter were more effective in reducing the flank wear of the tools. Th e increase of area fraction of sulfide inclusions resulted in reductio n of both the cutting force and the flank wear of the tools. There wer e two conflicting factors concerning the effects of both the shape fac tor and area fraction of sulfide inclusions on the surface finish of t he steel workpieces.