Microstructure and Strength Evaluation of EA4T Axle Steel Repaired by Laser-cladding
XIAO Peng1,2, GAO Jiewei3,4, LIU Ligen1,2, HAN Jing1,2
1 Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu 610031, China 2 School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, China 3 School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China 4 State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, China
Abstract: In order to prolong the service life and reduce the scrap rate of high-speed train axles, laser cladding remanufacturing was used to repair the damaged surface of axles. In this study, 24CrNiMo alloy powder was cladding on EA4T axle steel surface, and the effect of heat treatment(HT) on the properties of the cladding layer was investigated. The microstructure, microhardness and tensile properties of the cladding layer were analyzed by optical microscope(OM), scanning electron microscope(SEM), electron backscattering diffraction(EBSD), Vickers hardness tester and universal testing machine. The fatigue strength was measured by four-point bending experiments, and the fatigue fracture was observed. The results showed that the microstructure of the cladding layer was mainly composed of cellular dendrite, columnar crystal and fine dendrites with random orientation. The microhardness, tensile strength and yield strength of the cladding layer were much higher than that of the substrate because of the fine grain strengthening and the formation of tempered martensite. After HT, due to grain coarsening and the formation of tempered sorbite, the hardness and strength of the cladding layer decreased, while the plasticity and toughness increased, and the fatigue strength of the sample decreased compared with the original cladding sample. The fatigue fracture of EA4T steel after laser cladding was a micro-cleavage fracture with cleavage steps and tear ridge, and the fracture after HT appeared quasi-cleavage cracks.
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