NUMERICAL ANALYSIS OF LASER SURFACE HARDENING OF A MEDIUM CARBON STEEL.

The results of a FEM-simulation on laser surface hardening of a medium carbon steel are described. A 2-dimensional computer program was used to investigate the effects of travel speed and beam spot diameter on the shape and size of hardened zones. For the confirmation of the accuracy of the numerical analysis a medium carbon steel of 5-mm thickness was heat-treated with a 1-kw CO//2 laser. A simulation scheme for the cooling time and the corresponding CCT-diagram showed that the cooling rate is high enough to consider the heated zone above 723 degree C as the martensitic hardening zone. With proper assumption of the absorptivity the numerical and experimental shape and size of hardened zones were in good agreement. The numerical analysis showed that the beam mode has a considerable effect on the width and depth of lenticular-shaped hardened zones and for a constant heat input per unit length the heat input rate has a great effect, if the traverse speed is low. It was also found that there exists a range of beam spot diameters, which can produce optimal hardened zones for a given beam scanning speed.