Study On Microstructure And Mechanical Properties Of Laser Welded Joints About 2205 And 316L Stainless Steel

Laser welding is an efficient and precise welding method.Because of its high energy density,high precision and strong adaptability,it is widely used in the connection of engineering materials.316L stainless steel and 2205 duplex stainless steel are two kinds of good corrosion resistance,weldability and high strength of stainless steel,both of which are used in the marine environment,petrochemical and other corrosive environment.In the actual production,in order to meet the equipment requirements,while reducing costs,will inevitably encounter different types of stainless steel welding problems.There are large different physical properties and chemical composition in different stainless steel,in the use of traditional welding methods are often difficult to obtain excellent performance of welded joints.Therefore,in order to solve the heterogeneous stainless steel welding process in the microstructure and mechanical properties of non-uniformity problem,improve the comprehensive performance of dissimilar steel welded joints.In this paper,useing Nd:YAG pulsed laser processing machine,according to laser welding technology theory,through the single factor experiment.Experiment on Laser butt Welding of 316L Stainless Steel and 2205 Duplex Stainless Steel by Changing Welding Current,Pulse Width,Velocity and Frequency.The effects of welding parameters on the microstructure and mechanical properties of welded joints of dissimilar stainless steels were analyzed.The morphology,microstructure,chemical element distribution and fracture morphology of welded joint were studied by means of metallographic microscope and scanning electron microscope.The tensile properties and microhardness of the welded joints were analyzed by universal electronic tensile testing machine and Vickers microhardness tester.The dynamic signals of laser,such as light,electricity and heat were observed,collected and analyzed by high-speed camera,piezoelectric force measurement and infrared thermal imaging.The main conclusions are as follows:(1)During the welding experiment,it was found that the current and pulse width mainly affected the penetration depth and width of a single weld.The speed and frequency have a great influence on the heat input of the welded joint,which mainly determine the continuity of weld.In the 1mm butt welding,should use smaller current and pulse width,higher speed and frequency;in 2mm butt welding,should adopt the larger current and pulse width,lower welding speed.(2)The microstructure of the welded joint shows that the columnar grains and equiaxed grains are easy to be formed when the heat input is large in the welding parameters.A small amount of net ferrite and a large amount of strip austenite are present in the weld.The growth direction of the weld on both sides of the organization is asymmetric.(3)The element composition and the content of weld line are close to the base metal.Compare with the base materials,elements are mixing and dilution in the weld.The nickel content was changed from 5%(2205),10%(316L)of the base material to 8%.The chromium element content was changed from 25%(2205),17%(316L)of the base material to 20%.(4)Tensile test results show that the tensile strength of welded joints reached 620MPa,slightly lower than the base material 316L stainless steel,fracture occurs in the side of the 316L stainless steel.The penetration depth and width of the weld have the greatest influence on the tensile strength,and the microstructure has the second effect.(5)The welding speed and frequency have the greatest influence on the microhardness of the welded joint,followed by the current,the pulse width has the least effect on the hardness.2205 duplex stainless steel weld fusion line microhardness is high,reaching 320HV,increasing 10%,316L stainless steel weld fusion line microhardness is low,reaching 220HV,increasing 20%.(6)The tensile fracture morphology observation results show that:The mode of fracture in welding joint is ductile fracture,microvoid coalescence fracture.Under the same welding parameters,the toughness of the weld center on the upper part is the better,and the bottom of the weld toughness is poor.The toughness of the joint is better in the case of large heat input,and the toughness of the joint is smaller in the case of small heat input.(7)The size of molten pool,the solidification rate and the generation of splash are closely related to the welding parameters and have a great influence on the weld formation.The temperature field on both sides of the weld is non-uniform and the laser welding process produces almost no force.