Study On Process Of Laser Cladding Nickel Based Anti-corrosion Coating On The Inner Wall Of Oil Pipe

Oil pipelines have the characteristics of unlimited transportation direction and low transportation cost has become the main way to transport crude oil,most of which are made of low carbon steel,which is easy to corrode with crude oil compared with other steels,resulting in corrosion of the inner wall.At present,coating anti-corrosion is the main anti-corrosion measure,and laser cladding technology is a new process for preparing inner wall anti-corrosion coatings.Therefore,this paper uses laser cladding technology to prepare inner wall anti-corrosion coating,and further improves the microhardness and corrosion resistance of the coating by optimizing the forming process and preparing composite coating.The paper achieved the following main results:The temperature field model was established to optimize the forming process parameters,and the accuracy of the model was verified by experiments.ABAQUS was used to establish the temperature field model of laser cladding Inconel 625,and the temperature change law at the interface of coating and substrate was studied by a single-pass single-layer temperature field model,and the forming process parameters of laser cladding Inconel 625 coating were optimized,and the results showed that when the laser power was 1600W～2000W and the scanning speed was 600mm/min～800mm/min,the coating and substrate could be well combined.According to the above results,an experimental protocol was formulated to prepare a single-pass single-layer Inconel 625 coating,and the coating was well formed without obvious defects,which was consistent with the simulation results.Further analysis of the cross-sectional morphology of the molten pool and the relationship between the geometric parameters of the molten pool and the process parameters showed that the coating with a laser power of 2000W,a scanning speed of 600mm/min,a powder feeding speed of 0.082g/s and a dilution rate of 6.1%had the best forming quality,without defects such as porosity and cracks.The results of the top temperature and molten pool morphology in experiments and simulations were compared,and the error was small and the accuracy of the model was high.To study the effects of different levels and sizes of B₄C on the microstructure of Inconel625 coating.Firstly,the B₄C/Inconel 625 coating forming process was optimized,and the crack rate of the composite coating was reduced by increasing the line energy（the ratio of laser power to scanning speed）,and when the line energy was higher than 350J/mm,no surface cracks were produced in B₄C/Inconel 625 coatings with different content and different particle sizes.B₄C/Inconel 625 coating was prepared by using the process parameters of laser power of 3000W,scanning speed of 350mm/min and powder feeding speed of 0.057g/s,and then microstructure analysis was carried out,and the results showed that Inconel 625 coating was mainly composed of austeniticγ-Ni phase,with a large number of columnar crystals in the middle and bottom,and a small number of equiaxed crystals at the top.After the addition of B₄C,planar crystals exist at the interface between the coating and the substrate,forming a good metallurgical bond,resulting in Ni-Cr-Fe,Fe-Cr,（Fe-Ni）and NiB compounds.When the B₄C content is5wt.%～10wt.%and the particle size is 10μm～60μm,the number of equiaxed crystals increases significantly,and the coarse columnar crystals are also refined,which weakens the texture strength of the coating and effectively improves the microstructure of the Inconel 625 coating.Further study of the effect of B₄C on the microhardness and corrosion resistance of Inconel625 coating.For the microhardness of the composite coating,the hardness of Inconel 625coating is higher than that of the substrate,and the hardness of B₄C/Inconel 625 coating is improved to different degrees compared with Inconel 625 coating,and when the B₄C content is15wt.%and the particle size is 10μm,the average hardness of the coating is the highest compared with the Inconel 625 coating.For the corrosion resistance of composite coatings,when the B₄C content is 5wt.%,the coating has the lowest corrosion current density of 8.956E-7A/cm² and the maximum polarization resistance of 48833.2Ω/cm²,and the lowest corrosion current density of 1.289E-6A/cm² and the largest polarization resistance of 34021.1Ω/cm² when the B₄C particle size is 60μm.In summary,when the B₄C content is 5wt.%～10wt.%and the particle size is 10μm～60μm,the coating performance of Inconel 625 is effectively improved,mainly due to fine grain strengthening and solution strengthening.