레이저피닝을 이용한 스테인리스강의 표면 경도 강화

Enhancement of Surface Hardness of Stainless Steel by Laser Peening

Experimental results for the laser shock peening of stainless steels, duplex stainless steel and STS304, for the enhancement of surface hardness are reported. A high power Nd:YAG laser (532 nm, 2nd harmonics) was used to irradiate the workpiece in water at the irradiances of 5, 10, 15 GW/cm2. The surface of a workpiece was covered with Fe or Al foil for protection of the original surface and reduction of laser reflection. The laser pulse densities were varied from 25 pulse/mm2 to 75 pulse/mm2. In the case of the STS304, the surface hardness increased with increasing pulse density and the maximum increase of about 29% was achieved using Fe foil at 10 GW/cm2 and 75 pulse/mm2 conditions. The maximum increase in surface hardness of duplex stainless steel was about 8% at 10 GW/cm2 and 75 pulse/mm2 with also Fe foil. In the case of the Al foil, less increase of surface hardness was obtained, possibly due to the thermal expansion effect.