Influence of a cutting fluid on the surface integrity and fatigue strength of 42CrMo4 drilled parts.

This study investigates the influence of a cutting fluid during the drilling operation on the surface integrity and fatigue strength of 42CrMo4 hardened steel. The investigation includes characterizing surface topography, microstructure at different hole locations, and residual stresses. Fatigue tests were conducted, and the results were correlated with observations on surface integrity. The findings reveal that crack initiation occurs in a transition zone within the hole, where the cutting process evolves from pure cutting to a region with a strongly adhesive layer. The absence of cutting fluid leads to increased surface roughness and tensile residual stresses, resulting in a 28% reduction in fatigue strength.