Hard-turning-induced surface integrity and fatigue performance of 18CrNiMo7-6 steel for V-notched specimens

In conventional grinding processes for hardened steel, excessive residual tensile stress can negatively affect part performance. Additionally, using cutting fluids during grinding often causes environmental pollution. To address these issues, this study adopted dry hard turning (DHT) instead of grinding processing for fatigue specimens. This study focused on the DHT of 18CrNiMo7-6 hardened steel and examined how the DHT processing parameters affect the surface roughness, surface residual stress, and 3D surface morphology of 18CrNiMo7-6 hardened steel V-notch specimens. Additionally, fatigue tests and fracture analyses were performed to compare the fatigue performance of the specimens machined via DHT and grinding processing with the preferred parameters. The experimental results show that as the rotational speed (n) increases, the surface roughness (Ra) first decreases and then increases, whereas the residual compressive stress of the V-notch fatigue specimens first increases and then decreases. As the feed velocity (v_f) increases, Ra increases, and the residual compressive stress decreases. Under specific conditions, when n = 1200 rpm and v_f = 5 mm/min, Ra reaches a minimum of 0.259 μm, the axial residual stress reaches a maximum of −580.0 MPa and the tangential residual stress reaches a maximum of −420.6 MPa. Additionally, the surface integrity of the specimens machined via DHT is significantly superior to that of the specimens processed via conventional grinding, and the fatigue resistance of the DHT-machined specimens is superior to that of the specimens processed via grinding. The fatigue resistance of the DHT specimens is better than that of the ground specimens, which can realize “Turning instead of Grinding.”