The Study Of Underwater Wet Flux-cored Arc Welding Assisted By Ultrasonic Frequency Pulse High-current

Underwater welding is commonly used for routine maintenance work on cross-sea Bridges,undersea oil and gas pipelines,offshore floating Bridges and nuclear power plants.With the increasing of ocean engineering projects,higher requirements are put forward for welding efficiency and welding joint quality.Underwater wet cored welding overcomes the dry process and the local dry welding process is complex,high cost of drawbacks,in the case of drainage device does not need complex directly for welding in water environment,the method with high efficiency and high welding accessibility and easy to realize automation welding underwater welding development the main trend in recent years.However,due to the great interference of the water environment,this process method causes serious damage to the forming and quality of the welding seam.Therefore,many scholars put forward an improved underwater welding process without giving up the high efficiency.In this paper,underwater wet flux-cored arc welding assisted by ultrasonic frequency pulse high-current(UFPHC-UWFCAW)is one of them.In this paper,UFPHC-UWFCAW process mechanism analysis mainly through visual acquisition system analysis,organizational evolution system analysis and comprehensive performance test system analysis.The analysis of visual acquisition system focused on the evolution of "arc-bubble-droplet".Compared with UWFCAW and UFPHC-UWFCAW,it was found that the introduction of UFPHC can reduce the arc extinguished rate,reduce the disturbance caused by bubble expansion speed to the water environment,and improve the height of constriction and separation.This behavior effectively promoted the protection of droplet.Decrease droplet average size and increased droplet transition frequency.The influence of different ultrasonic parameters on "arc-bubble-droplet" evolution was studied.It was found that with the increase of UFPHC frequency,the bottom transverse size of bubble necking becomed more stable,the expansion speed was slower,the necking height was higher,and the effect was the best at 40 kHz.Finally,the combined effect of the "arc-bubble"stabilization process made the droplet transition mode optimized and the splashing behavior inhibited.On the other hand,it was found that the transverse size of bubble increases gradually with the increase of pulse current,and the droplet transition improved with the increase of pulse current.The systematic analysis of microstructure evolution focused on microstructure evolution,phase content,grain size,grain boundary and orientation difference.The study found that after joining the super audio could organize grain refinement,promote the proeutectoid ferrite in the weld to acicular ferrite,acicular martensite in the heat affected zone to lath martensite transformation and grain boundary ferrite,small Angle grain boundary distribution more uniform,the content of martensite in the heat affected zone and aggregation degree further reduced.By further exploring the ultrasonic frequency and pulse current and comparing different ultrasonic frequencies,it is found that 40 kHz has the best effect on refining the microstructure grain and reducing the martensite content in the heat-affected zone.Compared with different ultrasonic pulse currents,100 A is the best for refining the microstructure grain and reducing the martensite content in the heat-affected zone.The comprehensive performance test system analyzes the porosity of the weld,the hardness distribution of the welded joint,the impact toughness of the weld and the corrosion resistance of the weld.The final results show that the introduction of ultrasonic reduces the porosity of the weld,improves the hardness peak of the heat-affected zone,and improves the impact toughness and corrosion resistance of the weld.