Abstract
In order to assess an effect of MnS morphology on surface roughness of low carbon free cutting steel, a turning test using carbide inserts was demonstrated for two free cutting steels containing different type of MnS inclusions. No built-up edge was formed at top of minor cutting edge in the insert, which machined the steel containing globular MnS, but a groove-like wear with regularly-arranged depressions arose at flank face of the minor cutting edge. And, the surface roughness was proportional approximately to the depth of worn depression in the groove-like wear. In the other insert machined the steel containing smaller MnS, a large built-up edge was formed and it seemed to be caused the inferior surface roughness. A TEM assessment for cross section of the worn tool surface clarified that microstructure of α-iron layer, which adhered on the worn tool surface during machining, was composed of deformed fine grains. And it was found that WC particles worn away with sharp edge at the interface with the α-iron layer. Results in the TEM assessment suggested that diffusive wear of tool component into the adhering α-iron layer on the tool surface was likely explanation for the tool wear mechanism.
