Research On Ultrasonic Assisted Underwater Wet Welding Of E40/304L Dissimilar Steels

In recent years,welded joints of dissimilar steel have been used more widely in marine engineering,and the problems of dissimilar steel joints underwater restoration have been paid more attention to.Aiming at the difficulties of dissimilar steel underwater wet welding,this paper puts forward a new method named ultrasonic assisted underwater wet welding to weld dissimilar steel,in order to improve the microstructure of the welding joint,reduce defects,and improve the quality of joints of dissimilar steel.Firstly,ultrasonic assisted underwater wet bead welding test of dissimilar steel was carried out.The optimal welding parameters based on further experiments found in orthogonal test was obtained.When the wire feeding speed was 9m/min,the welding voltage was 30 V,the welding speed was 2.5mm/s,the contact tip to work distance was 15 mm,the weld formation was the best.With the increase of the welding voltage,the weld width increased,the weld reinforcement decreased,and the penetration depth did not change significantly.With the increase of wire feed speed,the weld width increased,the weld reinforcement also increased,and the penetration depth did not change significantly.With the increase of welding speed,weld width decreased,the weld reinforcement also decreased,and the penetration depth did not change significantly.When the radiation height was 70 mm,the ultrasonic effect on the weld surface forming quality was the most obvious.The quality of butt welds formed by ultrasonic assisted underwater wet welding was better than that of conventional underwater wet welding.Then the influence of radiation height,welding voltage and wire feeding speed on arc stability was studied.When the radiation height was 70 mm,the arc stability was the best.With the increase of welding voltage,the arc stability of two kinds of welding methods firstly increased and then decreased.When the welding voltage was 30 V,the stability of the welding arc was the highest.With the increase of welding voltage,the transition mode of droplet transfer changed from short circuiting transition to short circuiting transition and free transition to free transition.The effect of ultrasonic can reduce the ratio of arc breaking time and short circuit time,and increase the ratio of arcing time,so as to improve the arc stability.With the increase of wire feeding speed,the arc stability of the two welding methods decreased,and the droplet transfer mode changed from free transition to short circuiting transition and free transition.Finally,the effects of ultrasonic on microstructure and mechanical properties of wet welding joint with dissimilar molten steel was investigated.The microstructure analysis of the joint shows that the weld metal zone was composed of austenite and δ-ferrite,and the heat affected zone on the E40 side included four parts: coarse grained zone,fine grained zone,incompletely quenched zone and tempered zone.The microstructure of the heat affected zone on the 304 L side was composed of coarse austenite.The effect of ultrasound can change the columnar crystalline structure of the weld center to small equiaxed grains.Under ultrasonic,the width of the fusion zone on the E40 side decreased remarkably,and the alloy elements were mixed more evenly.Under ultrasonic,the tensile strength of the weld was improved.When the ultrasonic was applied,the tensile fracture of the weld was a typical ductile fracture.When the ultrasonic was not applied,the fracture surface of the weld had a mixture of ductile fracture and brittle fracture.Under ultrasonic,the impact toughness of weld was improved.When the ultrasonic was applied,the impact fracture of the weld was a typical ductile fracture.When the ultrasonic was not applied,the fracture surface of the weld had a mixture of ductile fracture and brittle fracture.Ultrasonic can increase the hardness of weld zone.