Improved three-point bending fatigue properties of surface-strengthened 42CrMo steel via pulsed magnetic field treatment

This study explores the efficacy of pulsed magnetic field treatment (PMFT) in improving the three-point bending fatigue properties of 42CrMo steel, while elucidating the associated multi-scale strengthening mechanisms. Comprehensive characterization, including fatigue testing, scanning electron microscopy (SEM) of fracture surfaces, residual stress measurements, microhardness profiling, static tensile properties, X-ray diffraction (XRD), and magnetic force microscopy (MFM), was employed. The results indicate a substantial 19.21% elevation in fatigue limit from 354 MPa to 422 MPa, accompanied by a transition in crack initiation from surface to subsurface sites and reduced secondary cracking on fracture surfaces. PMFT induced compressive residual stresses of −120.9 MPa at the surface (reversing initial tensile stresses of +58.6 MPa), increased surface hardness by 9.7% and the average hardness within the 0–5 mm subsurface region by 8.9%, elevated dislocation density by 22.8%, and improved yield strength by 10.7%. MFM revealed a shift from disordered, larger magnetic domains to ordered, finer stripe domains, indicating stress homogenization. These outcomes position PMFT as a non-contact, effective surface strengthening method for medium-carbon alloy steels, surpassing traditional mechanical treatments in preserving surface integrity and offering practical benefits for fatigue-prone components in aerospace and automotive sectors.