Abstract
Laser beam hardenling of 12%-Cr steel has been evaluated by using a continuous wave 3 kW CO$\_$2/ laser with a hardening mirror set. Experiment was performed on the optimum hardening condition with a laser power of 2.85kW and travel speed of 10 and 5 m/min. Multi passes have been alsotried to find the hardening characteristics of partly overlapped zone. The black paint to use at high temperature was adopted to increases the absorptivity of laser beam energy with the wavelength of 10.6 .mu. m at the surface of bese metal. The microstructure of the hardened layers was observed by using a light microscopy. SEM and TEM. A fine lamellar martensite formed in the hardened zones exhibits very high Vickers microhardness of 600 Hv, whereas the tempered martesite distributes in the base metal with Vickers microhardness of 240 Hv. It has been found that laser hardening with multi pass showed no significant drop of the hardness between adjacent passes.