A high powered YAG laser was applied to a carbon steels hardened surface with assistant gases such as air, oxygen, nitrogen, carbonic acid and argon. Effects of the assistant gas on the hardened zone were measured by hardness and microstructure.
The structure of the hardened zone underwent complete martensitic transformation, and its hardness ranged from Hv 750-800. Under identical laser irradiation conditions, the hardened zone showed various values depending on the type of assistant gas, and the gas flow rate. Remelting took place in oxygen assistant gas. These results were due to the heat of oxidation and the exothermic reaction. The experimental results indicated that the hardened zone was affected by the cooling of the assistant gas as well as oxidation reaction.
