Abstract: In this paper the influence of composition, shape and area fraction of freecuffing phase modified by Ca, RE and Ca-RE on machinability of sulfur system free-cutting steel has been investigated. The role of free-cutting phases in decreasing cutting force lowers in the following order, MnS, (Mn, Ca)S, MnS-RE2S3 and (Mn, Ca)S-RE2S3, but that in decreasing flank wear increases in the above mentioned order The improvement of shape of free-cutting phase is defrimental to the former role, but helpful to the tatter role the increase of area fraction of free-cutting phase is helpful to both them.

Key words: Cutting force, Machinability, Surface roughness, Wear