Abstract: In this article, laser transformation hardening of HT250 material by high speed axis flow CO2 laser was investigated for first time in China. Appropriate laser hardening parameters, such as laser energy power P(W), laser scanning rate V m/min), were optimized through a number of experiments. The effect of the mentioned parameters on the hardened zone, including its case depth, microhardness distributions etc ., were analyzed. Through the factual experiments, it is proved that axial flow CO2 laser, which commonly outputs low mode laser beam, can also treat materials as long as the treating parameters used are rational. During the experiments, the surface qualities of some specimens treated by some parameters were found to be enhanced, which does not coincide with the former results. Furthermore in the article, the abnormal phenomenon observed in the experiments is discussed. According to the experimental results, the relationship between laser power density q and scanning rate V is shown in a curve and the corresponding formulation, which have been proved to be valuable for choosing the parameters of laser transformation hardening by axial flow CO2 lasers, was also given.

Key words: Laser transformation hardening, Hardened case, Laser parameters, Cast iron