Use of the Scanning Electron Microscope to Study the Function of Manganese Sulphide Inclusions in Resulphurised Free-Machining Steels
The scanning electron microscope provides the means for a new approach to the study of the mechanism by which manganese sulphide inclusions affect the machinability of free-machining steels. The use of this instrument in the experimental work described here has led to the conclusion that manganese sulphide inclusions affect the machinability of resulphurised steels chiefly by promoting the formation of a stable built-up cap on the cutting edge of the tool, which protects the cutting edge and reduces the rate of tool flank wear. A mechanism, embodying phenomena which are construed to be peculiar to the machining of resulphurised steel, is proposed here to explain how manganese sulphide inclusions promote this built-up cap formation. This function of manganese sulphide in re-sulphurised steel differs from that advanced previously, which relies on the formation of lubricating films on the tool surfaces.
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