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Abstract

A machine component which is formed from a high alloy steel has, along a surface where the component is subjected to cyclic loading, a glaze in which the steel has a refined microstructure that resists spalling. Whereas the microstructure of the core underlying the glaze contains carbides of relatively large particle size, the microstructure of the glaze contains carbides of a much smaller particle size. For the most part the microstructure of the glaze comprises martensite and retained austenite in a fine dendritic network. The glaze is acquired by directing a laser beam at the surface, with the beam having sufficient energy and intensity to melt the component where it illuminates the surface, thus creating a puddle. Relative motion between the beam and the component advances the puddle over the surface. The molten metal in the previously illuminated region loses its heat to the underlying core of the component and solidifies, in effect undergoing a self-quench. The solidification is rapid enough to prevent the formerly dissolved carbides from consolidating into large particles and to prevent the martensite and retained austenite from growing into large grains.

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First Claim