Effect Of Welding Process On Microstructure And Properties Of UMCo50/Inconel600 Dissimilar Alloy Weld

Process burner is the key equipment in the field of coal water slurry pressurized gasification.It works in a harsh environment where it is not only eroded by solid,liquid and gas in the gasifier,but also corroded by corrosive medium at high temperature.Therefore,the process burners are generally made of cobalt-based or nickel-based alloys with good strength,corrosion resistance and oxidation resistance at high temperature.Aiming at the problem of dissimilar alloys welding between cooling water coil(made of Inconel600)and burner head(made of UMCo50),the orthogonal experimental design method was used to optimize the TIG welding process parameters in this paper.And the effect of ultrasonic vibration amplitude on the microstructure and properties of the welded joints was studied.Besides,the effects of four different welding wires,which were UMCo50,ERNi Cr-3,GH18 and ERNi Cr Co Mo-1 on the microstructure and properties of the welded joints were studied.The conclusions obtained in this paper not only provided data support and theoretical basis for the optimization of welding process of UMCo50 and Inconel 600dissimilar alloys,but also had important practicle value for life extention and safe operation of the process burners.The orthogonal test design which took the welding current,welding speed,interlayer temperature,gas flow rate and number of weld passes as optimization factors was carried out,after which the welding parameters were optimized as welding current 140A,welding speed 8cm/min,interlayer temperature 150?,gas flow 8L/min and weld passage layers2,during which the forming quality,defect grade,hardness of weds and instantaneous tensile strength of welded joints at high temperature were taken as the evaluation criteria.The validation test results showed that when one side welding under these conditions,the two sides of welds of UMCo50 and Inconel 600 dissimilar alloys were well formed and there were no internal defects in the welds.Ultrasound vibration was added to assist weld using the optimized parameters,and the results showed that with the increase of ultrasonic vibration amplitude in the range of 0-20 um,the grain refinement effect was obvious,and the microhardness and impact toughness increased while the heat corrosion resistance decreased.The microstructures of welded joints obtained by four kinds of welding wires were analyzed by metallographic microscope,scanning electron microscope and EDS.The results showed that the four kinds of welding wires could achieve good metallurgical bonding with base metal with optimized process parameters.Recrystallization occurred near the weld zone on the side of UMCo50,for which the grain size was obviously refined compared with the forged structure of the base metal;The grains near the weld zone on the side of Inconel600 grew up due to overheating.There were cast structure with coarse grains,and there were substructure such as cellular and cellular dendrites in the grains.EDS analysis results showed that the transition of ERNi Cr Co Mo-1 wire was smoother than that of the other three wires near the fusion line on both sides of the weld.The results of X-ray diffraction analysis of the welds obtained by four kinds of welding wires showed that the weld using UMCo50 wire was mainly cobalt-based solid solution and there were no second phase precipition.But there were second phase preciption in the welds using the other three welding wires.There were Cr2Ni3?Fe3Ni2?Ti Co3?Cr₄Ni₁₅W?Ni₁₇W₃on the matrix of?Co(fcc)in the weld using GH188 welding wire.The matrix phase of weld using ERNi Cr Co Mo-1 was Ni(fcc)with some Al0.9Ni4.22 and Ni Cu.The matrix phase of weld using ERNi Cr-3 was Ni(fcc),on which a small amount Cr2Ni3?Fe3Ni2 were distributed.The results of mechanical properties tests at room and high temperature(700?)showed that the weld strength using welding wire GH188 was the highest,followed by ERNi Cr Co Mo-1 and UMCo50,and the weld using ERNi Cr-3 had the lowest strength.In terms of impact toughness,the higher the strength,the lower the impact toughness.On the one hand,the amount of Co content in the weld had a significant impact on its strength at room temperature and high temperature,on the other hand,the precipitation of intermetallic compounds affected the mechanical properties of the weld.Although the strength at room temperature and high temperature(700?)of the weld was the lowest among the four kinds of wires when the wire was ERNi Cr-3,the strength of the weld was still higher than that of the base metal Inconel 600,so the ERNi Cr-3 welding wire could also meet the requirements of use in terms of carrying capacity of weld joints.The results of hot corrosion test at 700?by salt coating showed that the oxidation reaction took place mainly when using UMCo50 and ERNi Cr-3 welding wires,and the heat corrosion resistance was good and the corrosion rate was slow;when the welding wires were GH188 and ERNi Cr Co Mo-1,the oxidation-sulfuration reaction occurred,and the corrosion rate was higher than that of the other two materials,so the heat corrosion resistance is poor.The results of oxidation weight gain test at 700?showed that the oxidation resistance of the welds using four different welding wires had little difference,among which UMCo50 is the best.