Surface modification of roll by pulsed ND:YAG laser: bump formation caused by martensitic transformation

The morphologies of roll surfaces are modified with pulsed Nd:YAG laser and characterized by topography measuring instrument (WYKO-16 DRT2TC). Sombrero shaped bumps with diameters 230-250 /spl mu/m and heights 2-4 /spl mu/m are produced by out of focus laser beam. A quantitative model is proposed to predict the bump formation during martensitic transformation. The results show: the bump height caused by martensitic transformation is very small. The key factor of macroscopic bump formation on roll surface during laser texturing is surface tension of molten metal.