| Laser welding is widely used in the welding of stainless steel due to its high energy density,fast heating speed,small heat affected zone,low welding stress and small deformation.In this paper,4.4 mm thick high-strength 316 L stainless steel is used as the research object in the tank container.The 1500 W laser is used for flat butt welding to analyze the microstructure and mechanical properties of the weld.The variation of laser power,welding speed and defocusing distance is studied.The influence of mechanical properties;the application prospects of laser welding and plasma-tungsten inert gas hybrid welding in the tank container industry are also compared.The research results are as follows:Under the process parameters of laser power of 1350 W,welding speed of 0.8 m/min and defocusing distance of 0 mm,the solidification of the weld is in F-A mode,and the microstructure is austenite + ferrite at room temperature.The tensile specimen of the base metal showed obvious plastic deformation before fracture,and the fracture was fractured at 45°.The fracture mechanism was microporous aggregation fracture,and the fracture mode was ductile fracture.Keeping the welding speed and the defocusing distance unchanged,when the laser power is in the range of 1050-1200 W,the weld bead is formed without obvious defects,and the degree of oxidation on both sides is low.As the laser power increases,the degree of oxidation of the weld increases gradually.With the increase of laser power,the penetration depth,melt width,waist height and waist width have different degrees of increase,but the width and waist height are high.The increase of the waist width is smaller than the penetration depth.Keeping the laser power and defocusing distance constant,when the welding speed is in the range of 1.1–1.7 m/min,the weld is generally well formed without obvious defects.With the increase of welding speed,the degree of oxidation of the weld increases first and then increases,and the area of the weld heat affected zone decreases.With the increase of welding speed,the weld depth and waist height decrease less than the melting.The width and width of the waist are reduced.When the welding speed is 0.8 m/min,the tensile specimen is broken from the weld due to the presence of pores in the weld,and the tensile specimen at the other speeds is broken at the base metal.Keep the laser power and welding speed constant.When the defocusing distance is in the range of-2~1 mm,the weld bead is well formed.With the increase of defocusing distance,the oxidation degree of the welded joint decreases first and then increases,and the weld width and the area of the welded heat affected zone change little.With the increase of the defocusing distance,the weld depth is significantly reduced.However,the width of the melt,the waist height and the waist width are almost unchanged,and the penetration depth under negative defocus is greater.When the value is the same,the hardness of the positive defocus is slightly higher than the hardness of the negative defocus.In addition,it is also found that the laser power and the defocusing distance have a great influence on the penetration depth,and the welding speed has a great influence on the melt width,the waist height and the waist width.The mechanical properties and corrosion resistance tests of the welded joints obtained by LBW and PAW-TIG were carried out under the same conditions of welding heat input.The results show that the hardness,strength,tensile properties and corrosion resistance of LBW are better than PAW-TIG.Therefore,LBW has the possibility of replacing the PAW-TIG and is applied to the actual production of key structural components of the tank container. |
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