ON THE WHITE LAYER FORMED ON THE VACUUM OIL-QUENCHED HIGH SPEED STEEL.

When a polished section of high speed steel tempered after being vacuum oil-quenched is etched, a white layer about 15 to 40 mu thick is observed at the edge of the section. Some properties of the white layer produced on the specimen SKH-9 are clarified by means of an optical microscope, a micro-vickers hardness tester, an electron probe microanalyzer, and an X-ray diffractometer. The white layer is formed only on the specimen tempered after being vacuum oil-quenched. Carburization is the direct cause for the formation of the white layer. The resistance of the white layer to decomposition on tempering increases as the Cr content is increased. The maximum hardness zone composed of M//6C-type carbide and coarse martensite of high carbon content exists in the inside of the boundary between the white layer and the matrix.