Surface heat treatment of EnS steel using a 2kW continuous-wave CO 2 laser

A CO₂ continuous wave laser producing up to 2 kW continuous power over an area down to 2·0 mm² was used as a surface heater. The surface hardening of certain steels is possible through a martensitic structure produced by rapid cooling from an elevated temperature, provided the laser power P, beam diameter D _b , and transverse speed V are kept within certain limits. Since the heat from a laser all passes into the surface and is not generated internally as with induction heating, thermal distortion is low and depth of hardening is controllable down to very thin layers. In the present paper the operating limits of the three principal process parameters when hardening En8 steel are described and it is shown that the depth of hardening is closely correlated with the parameter P/√D _b V. The resulting microstructures are analysed and the upper and lower speed limits for effective hardening discussed. Since the experiments were arranged statistically the reproducibility of hardness traces is also described.