On the Relationship between Machinability and Inclusion Morphology of Ca Bearing Free Machining Steels

Abstract

The relationships-between machinability based on tool life and oxide inclusion morphology of calcium deoxidized Cr-Mo case hardening steels and carbon structural steels, melted by 2T arc furnace, were investigated.
The results are as follows:
1) In the case that the oxide inclusions in the calcium bearing free machining steels are A₂ type which are plastically deformed by hot rolling, the prolongation of tool life is ob. ained not only for cemented carbide tool but also high speed steel tool.
2) The oxide inclusions contributing to the formation of“Belag”on the cemented carbide tool face are those which soften or melt down at certain cutting temperature on the toal-chip contact surface.
3) Sulfur addition (0.07%S) to the calcium bearing free machining steels is effective for the chip breakability, but the effect is not clear for the tool life.