| The working environment of process burners used in field of coal-water slurry gasification is very severe,because of high temperature,oxygen-rich and sulfur-containing.After a period of service,the end face of process burner occurs radial cracks,and the radial cracks deepening will lead to the failure of process burners.In order to save cost,the process burner often continue to be used after repaired by surfacing.However,inclusions,porosity,cracks and other defects are easy to occur due to unreasonable surfacing process parameters,the service life of the process burner repaired is lower than that of the original parts.Therefore,choosing reasonable surfacing process parameters and surfacing layer material and improving the microstructure of surfacing layer have important engineering application value for improving the service life of process burner.In order to find out the failure mechanism and enhance the service life of the process burner repaired,Failure analysis was carried out by means of macroscopic observation,ultra-depth three-dimensional microscope,metallographic microscope,scanning electron microscopy and energy dispersive spectrometer.The welding process parameters of TIG filling wire which has the same components with base metal were optimized by orthogonal experiment design method.The effect of ultrasonic vibration on the microstructure and properties of surfacing layer was studied.In addition,Co-Cr-Mo-Si alloy powder was surfaced on UMCo50 plate and the microstructure and properties of Co-Cr-Mo-Si alloy surfacing layer were studied.The results of failure analysis showed that the failure mechanism of process burners under different working conditions was different.The mechanism of the No.1 failure burner was erosion wear and stress corrosion.The mechanism of the No.2 failure burner was oxidation-sulfuration corrosion and ablation at high temperature.Through orthogonal test to optimize the surfacing process of UMCo50,the optimum surfacing process parameters were: welding current 120 A,surfacing speed 12cm/min,interlayer temperature 50?,surfacing layer 3 layers.The validation test with the optimum parameters showed that the surfacing layer was well formed and there were no defects in the surfacing layer after X-ray detection.Ultrasound vibration with amplitudes of 10?m,15?m and 20?m was applied during TIG surfacing,and the microstructure and properties of UMCo50 surfacing layers were studied.The results showed that with the increase of ultrasonic amplitude in the range of 10?20 um,the grain of surfacing layers was refined gradually,the micro-pore in surfacing layer was reduced gradually.The phase of surfacing layers was composed of ?-Co(fcc)and ?-Co(hcp)under different ultrasonic amplitudes.The phase of surfacing layers was not changed by ultrasonic vibration.The introduction of ultrasonic vibration could improve the hardness and high temperature wear resistance of surfacing layers,but it was not conducive to the hot corrosion resistance of surfacing layers.When the amplitude was 20?m,the hardness and high temperature wear resistance of surfacing layer were the highest,and the hot corrosion resistance was the worst.In the process of surfacing Co-Cr-Mo-Si alloy powder on UMCo50 plate,Laves phases such as Co3Mo2 Si and Co Mo Si appeared in the surfacing layer besides ?-Co and ?-Co.Compared with the UMCo50 surfacing layer,the existence of Laves phase improved the hardness and high temperature wear resistance of the Co-Cr-Mo-Si surfacing layer,and the thermal corrosion resistance of the surfacing layer is lower than that of the UMCo50 surfacing layer due to the decrease of Cr content. |
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