Residual stress field analysis and life prediction of S38C carbon steel axle based on neutron diffraction

Liu, J. J.*; Qin, T. Y.*; Hu, F. F.*; Xu, P. G.   ; Su, Y. H.  ; Wu, S. C.*

The railway axles are critical components for high-speed trains, subject to complex fatigue loads from wheels, rails, and the car bodies, directly affecting service safety. Medium carbon steel S38C axles after high-frequency induction hardening retain a significant gradient of triaxial residual stresses down to a depth of several millimeters, raising concerns about their fatigue integrity. This study measures the axial, hoop, and radial residual strains within the axles for the first time using advanced neutron diffraction. Utilizing the SIGINI Fortran subroutine, we reconstructed the global initial residual stress field from the measured data, revealing residual stresses of approximately -520 MPa (axial), -710 MPa (hoop), and -40 MPa (radial) beneath the surface. We also investigated the fatigue crack propagation behavior of S38C axles through numerical modeling in the context of fracture mechanics, finding that compressive residual stresses within 0-3 mm of the surface reduce the driving force for crack growth, preventing propagation as long as the crack depth remains below 3.7 mm for hollow S38C axles. These results suggest that the maximum defect size allowed in routine inspections is safe.