Influence of laser shock peening on fatigue performance of LZ50 axle steel for railway wheel set

Laser shock peening (LSP) is a surface treatment technique that forms a strengthened layer on the metal surfaces. In this study, the LSP was applied on the locomotive LZ50 axle steel surface which was interference fitted with the wheel. The microstructures, fracture morphologies and fatigue performances of LSP-treated and untreated axle steels were explored. The results indicated that after the LSP treatment, a strengthened layer was generated on the axle steel surface. The surface hardness was increased by 25%, that is, from around 204 to around 255 HV0.3. The residual compressive stresses were improved from 260 to 345 MPa along the axial direction and from 165 to 225 MPa along the radial direction. The fatigue limit was increased by 30%, that is, from around 130 to around 170 MPa. The fracture surfaces could be divided into three regions: crack initiation, crack propagation, and short-break regions. In the crack initiation region, the fatigue striation of the LSP-treated steel was denser than the untreated steel. In the crack propagation and short-break regions, the fracture morphologies of the LSP-treated and the untreated axle steels were similar.