Determination of optimal ultrasonic surface rolling parameters to enhance the fatigue strength of railway axle EA4T steel

Abstract

The increasing complexity of railway services is placing higher demands on ensuring the fatigue resistance of critical components of high-speed trains. The ultrasonic surface rolling process (USRP) was employed to enhance the fatigue resistance of the EA4T axle steel used for high-speed trains in China. The optimal USRP parameters were first determined by orthogonal testing, with the rotational bending fatigue life as the evaluation index. Multidimensional experimental characterization and finite element simulation results demonstrated that the surface layer of the treated axle steel underwent violent plastic deformation, in which the grain size, hardness and geometrically necessary dislocation density showed distinct variation with depth from the surface. The surface roughness of the USRP-treated specimens was significantly less than for the untreated specimens, and the average compressive residual stress increased by a factor of 4.3. The 46.9 % increase in rotational bending fatigue strength (from 320 to 470 MPa) was attributed to the combined action of the large compressive residual stresses, the work-hardened surface layer, and less surface roughness. These results demonstrate that ultrasonic surface rolling is an effective surface hardening technique to improve the fatigue resistance of railway axles.