Study On Weldability Of High Nitrogen Austenitic Stainless Steel And GMAW Process With Twisted Wire

High nitrogen austenitic stainless steel is a kind of stainless steel owning high strength,high plasticity and excellent corrosion resistance.However,the escape of nitrogen from high nitrogen austenitic stainless steel is easy to occur in the welding process,which results in the formation of nitrogen pores and nutride.The defects reduce the mechanical property and corrosion resistance of high nitrogen austentic stailess steel and limit the widespread use of high nitrogen stainless steel.Twisted wire gas metal arc welding(GMAW)was employed to join the high nitrogen austenitic stainless steel to improve the mechanical property and corrosion resistance of welded joints.The paper focuses on the study about weldability and Twisted wire GMAW of high nitrogen austenitic stainless steel,which provides a theoretical basis for industrial application.The main works and conclusions are as follows:Research on weldability characteristics and the evolution of strengthening mechanism under the different welding thermal cycles for high nitrogen austenitic stainless steel.The results show that high nitrogen content can inhibit the formation of ?-ferrite and M₂₃C₆ in steel,and improve the strength,plasticity and corrosion resistance at the heat-affected zone.The strength of the heat-affected zone increases with the increasing of cooling rate.Plasticity is reduced and strength improved with the increasing of peak temperature.However,heat-affected zone weakens when the peak temperature is 1250?.Study on correlation between filling materials and weld joints.GMAW welding processes using Twisted wire and solid wire were employed to join the high-nitrogen stainless steel plates,and correlation was studied by comparing the arc behavior during welding,microstructure and mechanical properties.It is found that the molten pool rotates during welding,and the welding defects are reduced.Furthermore,the weld grain is refined,and compared with conventional solid single-wire,the yield strength and tensile strength are increased by 46.5%and 42.3%respectively.However,a brittle zone along the(?)-ferrite forms in welding seam after the welding using conventional solid single-wire ER307Si,which reduces the mechanical properties of welded joints.Based on Twisted wire single-wire GMAW,effect mechanism of twin-wire welding process of high nitrogen austenitic stainless steel on microstructure and mechanical property was explored.It was found that welding using twin-wire greatly improves the welding efficiency,but the yield strength and tensile strength are reduced due to the high heat input of twin-wire.Study on effect mechanism of microstructure on corrosion resistance of welded joints under the different thermal cycles.Tests for corrosion resistance of welded joints were conducted,and resuts show that high heat input and low cooling rate increase the corrosion resistance of welding seams,and reduce the corrosion resistance of heat-affected zone.Compared with the conventional solid single-wire ER307Si,Twisted wire TP-N1670 after welding has lower corrosion resistance.Study on effect mechanism of chemical compositions of welding wire on corrosion resistance of high nitrogen austenitic stainless steel welded joints.It is found that the increasing fractions of Cr and Ni and the decreasing of Mn and Mo can improve the corrosion resistance of welded joints.Furthermore,the effect by increasing the fraction of Cr and Ni and decreasing the fraction of Mn is better.