Finite element method(FEM)was used to analyze the temperature field,stress field,and thermo-mechanical coupling field of the piercing plug,and the maximum thermo stress,maximum coupling stress,maximum surface temperature,stress concentration area,and fatigue crack type were determined.And laser cladding+high-temperature slow oxidation composite treatment was carried out on 20Cr2Ni4 steel to improve the mechanical properties and high-temperature resistance of the plug.The FEM simulation results show that the thermo-mechanical coupling stress of the plug is the vector sum of thermo tensile stress and mechanical compressive stress.The coupling stress is dropped by about 5.7％compared with the peak value of thermo stress.The value of thermo-mechanical coupling stress is mainly affected by thermo stress,and the changing trend and distribution are mainly affected by mechanical stress.the failure of the plug originates from the crack source on the inner surface under the combined action of thermo fatigue and mechanical fatigue,and propagates radially outward to form fatigue cracks on the surface.The results of laser surface composite treatment show that after laser cladding and high temperature slow oxidation treatment,the surface hardness of 20Cr2Ni4 steel can reach 494 HV0.025,the surface strengthening layer is firmly bonded to the matrix,and the content of oxygen element in the matrix is less and more evenly,which effectively improves the service life of the plug.
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