Abstract: It is reported that laser-processing is effective to repair the heat checks, which are fine shallow cracks on a surface of die-casting dies. In this study, the rotating bending fatigue tests have been carried out to evaluate the fatigue characteristics of laser-processed hot working tool steel. Because test results are scattered, S-N curves are decided based on the evaluation of fatigue strength distribution. As a result, the fatigue strength of the laser-processed specimens decreases remarkably in comparison with that of base metal. However, it can be recovered to almost initial value by heat treatment at secondary hardening temperature. This procedure is also effective to decrease the scatter of fatigue strength. The laser-processing can be carried out at low cost and this method is effective for the extension of the work life of dies.

Key words: Hot working tool steel, Laser-processing, S-N curve, Fatigue strength, Reliability