Effect of laser power and powder feeding on the microstructure of laser surface alloying hardened H13 steel using SKH51 powder

Abstract

The surface of H13 steel was hardened with laser surface alloying by using an alloy powder (SKH51) and melting the surface with a Yb-YAG disk laser, at varying powder feeding rates and laser power. A laser speed of 70mm/s and a beam interval of 0.45mm, which were found to be the optimal conditions for productivity maximization in a previous study, were set as fixed conditions for this laser surface alloying process. Under these experimental conditions, a higher laser power caused an increase in the depth of the alloy layer, but a decrease in the surface hardness. On the other hand, a higher powder feeding rate increased the surface hardness, without causing any significant change in depth. The increased hardness is ascribable to the carbides formed from C, W, Cr, Mo, and V contained in the SKH51 powder at the dendrite boundary of the alloy layer along with the formation of 100-nm-sized lath martensite during the fast quenching of the molten portion. The hardness of the laser surface alloyed layer reached values up to 791Hv, which is 190Hv higher compared to the hardness obtainable through a common solid state quenching process. The laser-hardened depth could be maintained at 0.4–0.5mm.