Research On The Process And Mechanism Of 316LN Stainless Steel By Oscillating Laser-hot Wire TIG Hybrid Welding

With the increasing size of various equipment in the industrial field,welding of medium and heavy plates has become an indispensable technology in various large projects.At present,all kinds of arc welding methods are mainly used for the welding of medium and heavy plate,such as TIG welding,MIG welding,submerged arc welding,etc.These methods have the characteristics of low welding efficiency and excessive heat input,which tends to reduce the weld performance,and the laser can be better to overcome these problems,people have introduced laser into thick plate welding to obtain laser-arc hybrid welding,laser welding with filler wire and other methods.Although this has greatly improved the efficiency and quality of thick plate welding,the welding process is still difficult to avoid defects such as unmelted and pores.In order to ensure the welding efficiency and obtain high-quality welds stably,this paper proposes a scanning galvanometer laser-hot wire TIG hybrid welding method,which is used for nuclear power main pipeline austenitic stainless steel316 LN.First,the process experiment of oscillating laser welding was carried out,and three parameters of oscillating track,oscillating frequency and oscillating amplitude were selected to conduct single-variable tests respectively,and it was found that increasing the oscillating frequency and oscillating amplitude can reduce pore defects.After the oscillating amplitude increases,the area of the molten pool increases and the depth of the molten pool decreases,which provides more space for the bubbles to float and reduces the floating time.When the oscillating frequency is increased,the convection in the vertical direction of the molten pool is enhanced,which is beneficial to accelerate the escape of the bubble.The parameters of the process test are optimized.When the oscillating track is perpendicular to the weld,the oscillating frequency is 100 Hz and above,and the oscillating amplitude is 2 mm and above,the overall weld is well formed without defects.Then,the laser-TIG hybrid welding process test was carried out.The laser power,the distance between laser and tungsten and the oscillating frequency were selected for univariate process tests.It was found that under the premise of a certain total heat input,the greater the laser power,the higher the weld porosity.The larger the laser-tungsten distance,the worse the hybrid effect and the higher the weld porosity.During the test,it was observed that a conductive channel was formed between the laser and the arc to ensure the stability of the compounding process.Monitoring of the molten pool of oscillating laser-TIG hybrid welding showed that the area of the molten pool increased after the laser oscillated,and the front end of the molten pool was flattened.When the vertical oscillating track is used,the oscillating frequency reaches 100 Hz and above,and the oscillating amplitude reaches 2 mm and above,the composite weld pool is relatively stable.The preferred process parameters in the test are laser power: 2500 W,light-tungsten distance: 2mm and above,oscillating frequency: 100 Hz and above.Using the preferred process parameters of the two methods,a 5mm board simulation bottom welding butt test was carried out,and both well-formed welds were obtained.The structure of both welds is composed of austenite and skeleton ferrite.There is a certain width of equiaxed grain in the middle of the weld seam of the oscillating laser welding,which is mainly formed by the stirring effect of the oscillating laser on the molten pool.There is also an equiaxed grain area in the middle of the weld of the oscillating laser-TIG hybrid welding,but it is narrower than the former,and the range of the heat affected zone is wider than the former,which is related to the slower cooling speed of the weld after TIG welding.The tensile test results show that the tensile strength of the weld by oscillating-laser welding is592.98 MPa,reaching 96.8% of the base material,which is higher than the 559.59 MPa of the oscillating laser-hot wire TIG welding,the hardness of the two welds is equivalent.Afterwards,the oscillating laser-hot wire TIG with filler wire welding process test was carried out.The oscillating frequency,oscillating amplitude,hot wire current/wire feed speed and welding speed were selected for single variable process tests.It was found that the oscillating frequency and oscillating amplitude mainly affect the sidewall fusion Status,and the hot wire current/wire feed speed and welding speed mainly affect the weld filling amount.In order to further analyze the influencing factors of side wall fusion,the arc shape in the groove during the filling welding process was collected.The test phenomenon shows that when the oscillating frequency is low,the laser has an attractive effect on the TIG arc in the groove.When the oscillating frequency is too high,The oscillating laser has almost no attraction to the arc,while the increase in the oscillating amplitude can enhance the attraction of the laser to the TIG arc.After analysis,it can be seen that the suppression of the unmelted defects of the side walls of the narrow gap filling welding mainly depends on the direct heating of the oscillating laser and the stirring effect of the molten pool,and the arc deflection plays a role in assisting the side wall fusion.Finally,the preferred filling welding process parameters were combined with the previously determined bottom welding method to complete the 20 mm thick plate narrow gap filling welding test.Compared with the conventional hot wire TIG welding,the former has a tensile strength of 623 MPa,which is higher than the latter’s 535 MPa The longitudinal hardness of the weld increases gradually from top to bottom,which is related to the gradually refined grain structure.