Performance Impact And Mechanism Research In The Pre-torsion Of EA4T Steel

The improvement of train running speed demands higher and stricter requirements of the performance of railway and train. The axle is an important component part of train, so the mechanical properties of the material not only determines the probable running speed, but also directly affect the safety of train transport. Currently, EA4T axle steel has been widely used in high-speed heavy-load locomotives. However, researches of pre-torsion processing are few. Based on experiments, this article processes the pre-torsion of EA4T, tests the mechanical properties of materials and to explore its performance optimization mechanism.With the aid of torsion and tensile testing machines, micro-hardness, fatigue testing machine, XRD diffractometer and other mechanics and microscopic testing methods, the article makes a systematic study of EA4T steel from common mechanical properties, microstructure, stress, and dislocation.By testing properties before and after torsion of EA4T steel, it is found that the mechanical properties of periphery sample are superior to core sample. After pre-torsion processing, the yield strength is highly enhanced; tensile strength fluctuates within a small range, while the plasticity descends. The hardness of the sample enhanced, and increases with the decreasing distance from the surface. The fatigue limit of the sample is also enhanced after torsion, carrying out SEM observation of fatigue fracture, analyzing fracture characteristic of the crack original area and propagation region area as well as final fracture area.With aid of microscopic observation and XRD techniques, exploring the torsion mechanism, comparing microstructure of the periphery and the core sample, it can be seen that the volume fraction and the size of the ferrite gradually increases from the periphery to the core, and influences material mechanical properties along the radial direction. By XRD test, measuring macroscopic stress and sub-grain size and micro-strain after torsion material, to get dislocation density and makes quantitative analysis of dislocation density. Material macroscopic stress is compression stress which can improve fatigue limit of alternate loading sample, grain refinement can enhance the material’s strength and plasticity, while dislocation density can significantly enhance the material’s strength, but will reduce ductility. In the reverse process, the dislocation density plays a primary role.