Surface transformation of DF-2 steel after continuous mode laser irradiation

Successive irradiation of DF-2 cold work tool steel was performed using a Nd:YAG millisecond pulsed laser with different feed rates in the range of 1–4 mm/s. Influence of the laser feed rate on the surface morphologies of the irradiated area was investigated by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDX) and three-dimensional Talysurf surface profilometer. Results showed the changes of surface morphology were depended on (i) the interactive nature of the surface with the irradiating laser; (ii) the feed rate of the laser; (iii) surface melting or phase transformation. Correlation of the changes of morphology with the measurements of surface roughness indicated that surface smoothening was normally obtainable at a relatively higher irradiating laser feed rate, and phase transformation would likely be an important mechanism in coalesce of original machining furrows for smoothening the irradiated surface.