Surface modification of DF-2 tool steel under the scan of a YAG laser in continuously moving mode

Pulsed Nd:YAG laser with focus diameter of 1.06 μm was used to treat successively and continuously the surface of DF-2 cold work tool steel plate. Surfaces irradiated under a large range of laser setting parameters resulted in very different morphologies and microstructures. Roughness of the treated surface was measured by Talysurf profilometer, whilst surface morphologies and microstructures were investigated by scanning electron microscopy (SEM). Change of crystalline structure and composition of the treated surface layers before and after treatments were studied by energy dispersion spectroscopy (EDX). Cross-sectional micro-hardness of the treated layers was also analyzed. Measured micro-hardness values clearly indicated the performance improvement of the treated surface owing to the formation of martensite. Penetration depth of the micro-hardness varied greatly with the laser irradiating parameters that recursively results in different microstructures. Suitable control of the laser irradiation parameters allowed the accomplishment of highest micro-hardness at the outermost surface.