| As the most traditional marine steel,45# steel has low prices and simple production processes.However,as a marine steel,45# steel has low corrosion resistance and high navigation resistance.However,preparing microstructure on its surface can effectively reduce resistance and improve corrosion resistance by preparing niobium carbide coatings.However,at present,most scholars have prepared microstructures on polymer surfaces or soft metal surfaces(Al),and few have conducted relevant research on preparing niobium carbide coatings in TD(Thermal Diffusion)salt baths after preparing microstructures on steel surfaces.In this paper,the surface of 45# steel with a width of 100-150 was prepared by molding method μm,depth 50-80 μm arc microstructure,followed by the preparation of a niobium carbide coating on the surface of 45# steel using TD salt bath technology at900 ℃-1000 ℃.The morphology,microstructure,and phase composition of the coating were analyzed.By measuring the coating thickness in different regions of the microstructure,a classical dynamic model of the coating thickness in different regions was established,and the formation process and mechanism of the coating in different regions of the microstructure were analyzed.The corrosion resistance and wear resistance of four samples with or without microstructure and niobium carbide coating were tested using electrochemical equipment and friction and wear equipment,respectively.The main conclusions are:(1)Comparing the surface microstructure morphology of 45# steel after normal temperature molding and hot pressing with molybdenum wire,blade,and diamond wire,it was found that the arc-shaped microstructure prepared by molding with 0.2 mm diameter diamond wire on the surface of 45# steel had the best effect,with a groove width of about 114.89 μm.The groove depth at both left and right ends is approximately72.34 μm.The optimal pressure for molding is 13 MPa.Through metallographic microscope observation,it is found that the degree of tissue deformation varies in different areas of the microstructure after molding.(2)After TD salt bath treatment,the niobium carbide coating layer at the bottom of the microstructure is the thickest,and the microstructure edges and corners are the thinnest.The coating thickness in different areas varies from large to small,ranging from A>B>C>D.According to the calculation of the classical kinetic model,the diffusion activation energy Q of niobium carbide in the three regions A,B,and C is224.90 kJ/mol,237.47 kJ/mol,and 253.67 kJ/mol,respectively.Plastic deformation increases the dislocation density and distortion energy in the region A,resulting in an increase in the diffusion coefficient of carbon in this region,a decrease in the diffusion activation energy,and a decrease in the carbon source leads to an increase in the diffusion activation energy in the region C.(3)In terms of corrosion resistance,the sample with a microstructure of niobium carbide coating has the highest self corrosion potential,the lowest self corrosion current density,and the highest impedance modulus.After being corroded by 3.5 wt.% NaCl solution,the surface basically does not change(the corrosion situation is not obvious),and the surface is still a granular niobium carbide coating.(4)In terms of wear resistance,planar niobium carbide coatings have the best wear resistance in atmospheric environments.Under simulated marine environment,the microstructure niobium carbide coating has the best wear resistance,and the average friction coefficient is stable at about 0.20.The friction coefficient and frictional mass loss of the four samples in simulated seawater environment(3.5 wt.% NaCl solution)are all smaller than their corresponding friction coefficient and frictional mass loss in atmospheric environment.The wear mechanism of samples without niobium carbide coating is adhesive wear,while the wear mechanism of samples with niobium carbide coating is abrasive wear accompanied by fatigue shedding. |
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