Influence of laser polishing on the high cycle fatigue strength of medium carbon AISI 1045 steel

Abstract Laser polishing is a surface treatment which is becoming a feasible alternative to mechanical processes such as conventional polishing and grinding, in a number of applications including moulds and dies. Being a relatively new process the knowledge of its effects on the fatigue behaviour is very poor. This research deals with the influence of laser polishing in the absence of an inert gas on the high cycle fatigue (HCF) of AISI 1045 steel. The experimental part of the work includes tests on tensile properties, surface roughness, residual stresses together with fatigue tests of mirror and laser polished specimens. The fatigue behaviour is slightly related to the surface roughness but mostly to the microscopic properties of the surface resulting from the melting and evaporation of material and the remainder of the heat affected zone (HAZ). A theoretical study, based on the experimental results, is addressed to obtain quantitative values of the fatigue strength useful for the analysis and design of laser polished components. It will also be demonstrated that laser polishing improves the HCF behaviour of AISI 1045 steel components whose surface roughness before laser polishing is higher than a threshold value.