Effect Of Shielding Gas On Microstructure And Performance Of BN4 Austenitic Stainless Steel Fiber Laser Welded Joints

BN4 austenitic stainless steel is a chromium-manganese-nitrogen austenitic stainless steel developed by replacing the expensive nickel with manganese and nitrogen.Due to its good corrosion resistance,and its cold and hot processing properties,BN4 is extensively applied in the fields of construction,energy,transportation,etc.Generally,austenitic stainless steel contains a small amount of ferrite phase,which can improve welding thermal crack resistance and corrosion resistance of austenitic stainless steel.BN4 austenitic stainless steel tends to cause the loss of nitrogen during the welding process,which makes the ferrite content in the weld seam high,thereby reducing the mechanical properties and corrosion properties of the welded joint.By using different shielding gases to increase the nitrogen content in the weld,the ferrite content the carbon/nitrogen compound content in the weld is controlled within a reasonable range,therefore the welded joint has good mechanical properties and corrosion properties.This article focuses on the weldability and shielding gas of BN4 austenitic stainless steel in laser welding to provide a theoretical basis for practical applications.The main research work has the following aspects:(1)The influence mechanism of different shielding gas types and flow rates on the metal vapor temperature field and velocity vector field in the welding process is studied.The test results show that when the same shielding gas is used,the height of the metal vapor gradually decreases with the increase of the shielding gas flow;when the same gas flow and different shielding gases are used,compared with argon as the shielding gas,nitrogen is used as the shielding gas.When,the height of the metal vapor is smaller.(2)The influence of shielding gas on the formation,microstructure,element distribution,austenite and ferrite content of welded joints was studied.The test results show that: using different shielding gases,the weld surface is slightly oxidized,and no obvious defects such as undercut,spatter,deformation,etc.are observed.All three shielding gases enable the weld surface have a good shape.Compared with argon as a shielding gas,when nitrogen is used as a shielding gas,the nitrogen content in the weld is significantly increased,which lead to the improvement of austenite content meanwhile.(3)The mechanism of the shielding gases on the mechanical properties and(4)corrosion properties of BN4 austenitic stainless steel fiber laser welded joints was studied.The test results show that the microhardness of the weld seams under different shielding gases is higher than the base metal.Compared with argon,the microhardness of the welds using nitrogen is significantly improved.All tensile specimens under different shielding gases fractured at the base material,indicating that the tensile strength of the weld seams was higher.Compared with argon,the weld under nitrogen protection has better corrosion resistance.In this paper,fiber laser welding tests of BN4 austenitic stainless steel executed through different shielding gases.Through study,the weld seam has a good shape,the ferrite content in it is controlled within a reasonable range,and the welded joint has good mechanical properties and corrosion properties.