Welding With Local Water Mist Cooling Technology For Multi-arc Submerged Arc Welding Of Pipeline Steel

Multi-arc submerged arc welding is a welding method in which multiple wires form multiple arcs to burn in a common weld pool.During the welding process,multiple arcs are coupled with each other,which can improve the metal cladding efficiency while obtaining good weld topography,so that the multi-arc submerged arc welding has the advantages of good forming quality and high production efficiency.And it have become an essential welding technology in industrial fields of pipeline steel pipe manufacturing.However,the large heat input of multi-arc submerged arc welding is likely to cause the impact toughness of the weld to decrease,which reduces the performance reserve of the joint,and restricts the development of oil and gas transmission steel pipes to the direction of large transportation capacity of thick-walled,large-diameter,and high-grade steel.The welding with local water mist cooling neutralizes the heat of the welding process through the evaporation of the water mist,which can reduce the heat input of multi-arc welding,adjust the microstructure of the weld joint,and improve the joint mechanical properties.This paper proposes a welding with local water mist cooling process method for multi-arc submerged arc welding of medium and heavy plates,and carries out the optimization of the process parameters of water mist cooling strength and the analysis of the morphology,microstructure and mechanical properties of the welded joints.Improper water mist control will contaminate the welding flux or molten pool,which will directly lead to welding defects such as pores and cracks,which greatly deteriorate the weld performance.In this paper,a back cooling source multi-arc welding test platform with quantitative control of multi-chilling parameters is constructed,which lays the foundation for the research of multi-arc submerged arc welding with local water mist cooling process.These parameters,such as water flow rate,gas pressure,spray distance,cooling source application position and length(number of nozzles),are the key factors to characterize the water mist cooling intensity,which directly affect the cooling capability and the scope of action of the joint heat affected zone during multi-arc welding.In this paper,the method of "high-speed camera + thermocouple temperature measurement" was used to study the internal relationship between chilling process parameters such as water flow rate and gas pressure,and the shape and cooling intensity of water mist.The research shows that the cooling effect is the best when the water in the mist is saturated,the atomization is uniform(no large droplets),and the stiffness is good.Based on the optimized water mist cooling parameters,this paper studied the effect of welding with local water mist cooling on the joint morphology.Compared with natural cooling,the welding with local water mist cooling can greatly reduce the width of the heat affected zone.Under the test conditions of this paper,the width of the heat-affected zone was reduced by 48.3%,and the effect of water mist chilling on the joint was obvious.Grain refinement,M-A component refinement and dispersion distribution will greatly improve the performance of pipeline steel.Through the comparative test analysis of X80 steel natural cooling and multi-arc submerged arc welding with local water mist cooling,the effect of grain refinement by welding with local water mist chilling was obvious,and the M-A components in the joint structure were refined and dispersed.The mechanical test study shows that compared with natural cooling,the impact absorption energy of welding seam and heat-affected zone of multi-arc submerged arc welding with local water mist cooling was greatly improved.Under the test conditions of this paper,the weld increased by 25.1%,the heat affected zone increased by 37.8%,and the hardness tended to be uniform,and the embrittlement and softening of the joints were weakened.It shows that the welding with local water mist cooling process method proposed by multi-arc submerged arc welding can effectively improve the microstructure and mechanical properties of welded joints of medium and thick plates,and greatly improve the performance reserves of the joints.It has shown application prospects in the fields of multi-arc welding such as oil and gas steel pipe manufacturing,ship splicing,etc.