Hot compression deformation behavior and microstructure evolution rule of a high-speed railway axle steel

The high performance of high-speed railway axle (HSRA) depends on the stress-strain state and microstructure formed in the hot processes, it is necessary to investigate the deformation behavior and microstructure evolution during hot uniaxial compression. Hot compression test was performed on specimen of a HSRA steel 25CrMo4 at a deformation temperature of 1040-1160^oC at a strain rate of 1.0-10.0 /s using a Gleeble thermal mechanical simulator. During hot compression test, samples were compressed to different true strain: 0, 0.2, 0.4, 0.6 and 0.8. Hot compressive deformation behaviors and effects of processing parameters, including forming temperature, strain rate and deformation degree, on microstructure evolution of HSRA steel 25CrMo4 are investigated and studied by metallurgical analysis. Experiments results show that the peak value of flow stress increases about 30 MPa at a certain deformation temperature when the strain rate increases from 1.0 /s to 10.0 /s. At a certain strain rate, the peak value of flow stress increases about 20-30 MPa when the forming temperature decreases about 60oC. The average grain sizes increases with the increasing of forming temperature at a certain strain rate and a given strain. For a given forming temperature, grain size decreased before the critical strain of 0.4 and increased after strain of 0.4 due to grain growth, especially at lower strain rate. Therefore, grain size at lower strain rate is larger than that at higher strain rate when true strain reached 0.8.