Mechanical properties and microstructure of the heterogeneous DZ2 axle steel under high-strain-rate compression at ambient temperature

This study aims to clarify the mechanical properties and deformation characteristics of the newly-developed DZ27CrNiMo (DZ2) axle steel for the China standard electric multiple units under dynamic loadings along the diameter direction of the axle at room temperature. The DZ2 axle steel has a heterogeneous band structure consisting of equiaxed grain and lath morphology tempered martensite. When being impacted at the strain rate range from 500 s−1 to 2440 s−1, its yield strength, compressive strength, and plastic strain increase. The flow stress upturn after yielding mainly depended on the strain rate effect rather than the work hardening due to the suppressed dislocation cross-slip. Meanwhile, the steady plasticity was consistent with the presence of uniformly distributed dislocations and microbands within the heterogeneous laminates. Although the nanoscale adiabatic shear bands (ASBs) and micro-cracks were found to initiate at the high strain rate of 2440 s−1, their propagation could be inhibited by the hard-tempered sorbate laths. As a consequence, an excellent resistance for impact-induced fracture was realized in DZ2 axle steel. Taking the thermal activation damage evolution into account, a modified Zerilli-Armstrong (ZA) constitutive model was proposed to describe the dynamic mechanical behavior of DZ2 axle steel. The modeling results were consistent with the experimental data, indicating a high prediction accuracy and good application availability in the operation and maintenance of DZ2 axle.