Development of Laser Carburizing Process using Hydrocarbon Gas

New laser carburizing quench process using hydrocarbon gas as the assist gas was proposed to strengthen ultra low carbon steel sheet. In this paper, the effect of CH4 concentration and various laser radiation parameters on hardness and area of fusion zone was investigated. Tensile strength of laser treated specimen were measured. The results of the present work were summarized as follows, (1) By using CH4, fusion zone with vickers hardness of more than 400 was obtained. (2) Hardness and area of fusion zone were well controlled by CH4 concentration, laser power, focal position, beam scanning rate and so on. (3) Tensile strength of laser treated specimen was about 20% higher than that of base metal. (4) CO2 laser carburizing apparatus consisting of the nozzle head and the exhaust of CH4 was newly developed, which enabled to strengthen ultra low carbon steel without breaking focal lens and the combustion of CH4.