The influence of laser re-melting on micro-structure and hardness of gas-nitrided steel

In this paper, modification of nitrided layer by laser re-melting was presented. The nitriding process has many advantageous properties. Controlled gas nitriding was carried out on 42CrMo4 steel. As a consequence of this process, ɛ+ɣ’ compound zone and diffusion zone were produced at the surface. Next, the nitrided layer was laser re-melted using TRUMPF TLF 2600 Turbo CO₂ laser. Laser tracks were arranged as single tracks with the use of various laser beam powers (P), ranging from 0.39 to 1.04 kW. The effects of laser beam power on the microstructure, dimensions of laser tracks and hardness profiles were analyzed. Laser treatment caused the decomposition of continuous compound zone at the surface and an increase in hardness of previously nitrided layer because of the appearance of martensite in re-melted and heat-affected zones.