Investigation of the effect of surface transformation hardening by high power diode laser on the microstructure, hardness and wear behavior of AISI O1 cold work tool steel

In this study, surface transformation hardening of AISI O1 cold work tool steel was investigated by use of a high power (1600 W) diode laser apparatus. In order to evaluate the effect of laser hardening, different output powers and scanning rates were applied and microstructures and phases were characterized, as well as micro-hardness and wear resistance were measured. The hardening treatment resulted in formation of a hardened zone of about 2 mm depth and up to 10 mm width at the surface of sample. The microstructure of this hardened zone was comprised of martensite and residual austenite; average surface hardness of the samples treated under various set of variable parameters was 650 to 760 Vickers. Increase of heat input caused increase of residual austenite content and formation of coarse martensite structure so that the least hardness was obtained for the sample processed by the highest heat input. Comparing wear resistance of laser hardened samples with traditionally quench-temper hardened and annealed specimens, it was revealed that the laser hardening process improves wear resistance of hardened samples so that wear resistance of the samples hardened via laser was about 10 times of the annealed ones.