Microstructural and hardness investigation of hot-work tool steels by laser surface treatment

Laser surface treatment technologies have been used to improve characteristics of wear and to enhance the fatigue resistance for mold parts. The objective of this research work is to investigate the influence of the process parameters, such as power of laser and defocused spot position, on the characteristics of laser surface treatment for the case of hot-work tool steels. CW Nd:YAG laser is selected as the heat source. The optical lens with the elliptical profile is designed to obtain a wide surface hardening area with a uniform hardness. From the results of the experiments, it has been shown that the maximum hardness is approximately 824 Hv when the laser power, focal position and the travel speed are 1095 W, +1 mm and 0.3 m/min, respectively. In addition, the surface heat treatment width using the plano-convex lens was three times larger than that using the defocusing of laser beam. In samples treated with lower scanning speeds, some small carbide particles appear in the interdendritic regions. This region contains fine martensite and carbide in proportions which depend on the local thermal cycle.