Comparative study of laser surface hardening of 50CrMo4 steel using continuous-wave laser and pulsed lasers with ms, ns, ps and fs pulse duration

Laser surface hardening, used to achieve hardened surface without affecting bulk properties of steels, generally employs continuous-wave laser to do the job. The purpose of this paper is to systematically investigate the use of different pulsed lasers for surface hardening of 50CrMo4 steel. A continuous-wave laser and various pulsed lasers with pulse duration ranging from fs to ms were used for the experiment. It was found that millisecond laser utilizing about 9 times lower power is as effective as continuous-wave laser for surface hardening. It produced an average surface hardness of ~719 HV (2.7 times higher than base material hardness) and ~200 µm hardened depth, which is comparable with continuous-wave laser hardening. Similarly, nanosecond laser could induce both surface hardening effect and material removal depending on the parameters used. However, a shallow hardened depth (of mere ~80 µm) was achieved compared to continuous-wave laser. Furthermore, femtosecond and picosecond lasers did not produce any observable surface hardening effect; instead they resulted in direct surface ablation.ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio