Underwater laser hardening of bearing steels

Abstract

Water can act as an effective cooling agent during processing of materials. This can be beneficial especially for surface hardening of steels whereby a rapid quenching rate is desired to generate a hard martensitic surface layer. In this study, the underwater laser hardening of bearing steels is experimentally investigated using a fiber laser. The study found that underwater laser hardening increases surface hardness by about 3.5 times than that of the base material which is higher than in conventional laser hardening. Surface hardness as high as 900 HV is achieved when processed with a thin layer of water above the steel surface. However, the depth and width of the laser hardened zone are found to be significantly smaller than in conventional laser hardening. Further analysis revealed that irregular hardened track formed at slower scanning speed due to the convective motion of water and shock wave generation.