Machinability of Steels After Heat Treatment with CO₂ Laser and Its Improvement

Abstract

This study deals with the machinability of steels after heat treatment with CO₂, laser using h-BN powder and blast furnace slug as absorbent. h-BN is well known as solid lubricant. As for blast furnace slug, its composition is similar to that of inclusions in calcium dioxide steel that shows good machinability. The absorbance of slug and h-BN were more than 80%, so it is said that these powders can be used as absorbent for CO₂, laser. Only in the case of h-BN, absorbent was melted into substrate and its depth was about 200 μm. When turning the steels after laser heat treatment using h-BN power and blast furnace slug as absorbent, carbide tool showed smaller tool wear than the case of carbon type absorbent. In the profile of the machined surface, there was a wave of about 5 μm in amplitude and its wavelength was equal to the feed rate of laser in heat treatment. This is because the workpiece surface after laser heat treatment has a periodic distribution in hardness. The hardness in the surface layer of workpiece was higher than that of the substrate.