Microstructure Of 304 Arc Stainless Steel Plasma Arc Welded Joint And Performance Studies

The 304 austenitic stainless steel have excellent corrosion resistance,good comprehensive mechanical properties and excellent weldability was widely used in pressure vessels,nuclear power,pipelines,machinery and shipbuilding industries.However,with the increase of the thickness of the plate,especially for the medium and heavy plate,the difficulty of forming the weld once was correspondingly increased,and the welding quality was difficult to guarantee.In order to improve the reliability of 304 stainless steel plasma arc welded joints,this paper selects 10mm thick 304 stainless steel.Microstructure,mechanical properties and corrosion resistance of plasma arc welded joints under different heat input conditions were studied and the effects of solution treatment and post-weld heat treatment on the microstructure and properties of welded joints were studied.The effects of welding heat input on the microstructure,mechanical properties and corrosion resistance of welded joints were studied.The orthogonal test was earried out with the tensile strength as the optimization target to optimize the welding process parameters.The results show that with the increase of welding heat input,the 6 ferrite content in the weld zone gradually decreases,the particle size of the heat-affected zone grows significantly,and the(Fe,Cr)23C6 carbide precipitates along the austenite grain boundary;As the welding heat input increases,the tensile strength gradually decreases.The impact toughness of the weld was higher than that of the heat affected zone.The higher the welding heat input,the smoother the surface of the weld and the heat affected zone,and the dimple becomes smaller and shallower.The hardness of the weld zone and the heat-affected zone was increased,and the hardness of the weld zone was always the highest;the higher the weld heat input,the worse the corrosion resistance,the increase of the weld heat input,and the cooling rate of the weld was reduced;the order of influence of orthogonal test factors on tensile strength was welding current,plasma gas flow and welding speed.The optimal combination of process parameters was:plasma gas flow 5.6L/min;welding current 270A;welding speed 180mm/min.A regression equation between the experimental welding process parameters and the tensile strength was established by regression analysis.The effect of solution treatment temperature on the microstructure and properties of the joint was investigated.The results show that with the increase of solution time,the content of ? ferrite in the weld and heat affected zone decreases,the heat affected zone and the base metal structure coarsen,and the weld,heat affected zone and parent metal(Fe,Cr)23C6 As the solid solution time prolongs,it gradually dissolves.At 950?,1000?,and 1050?,the corrosion resistance increases with the increase of solid solution time.At 1100? and 1150?,the corrosion resistance decreases with the increase of solid solution time.The corrosion resistance of the base metal increases with the extension of the solution time.The hardness of the weld zone,heat affected zone and base metal zone were all decreasing,and the hardness of the weld was decreasing first and then slower;With the increase of solution temperature,the dissolution rate of ? ferrite in weld and heat affected zone increases,the grain growth rate in heat affected zone and parent metal zone became larger,and the dissolution rate of carbides such as(Fe,Cr)23C6 increases.The corrosion resistance of the weld was firstly increased and then decreased.The corrosion resistance of the base metal was gradually increased.The corrosion resistance of the weld was best at 1000? for 2 hours.The hardness of the weld,heat-affected zone and base metal decreased with the increase of heat treatment temperature.The effects of post-weld heat treatment time and temperature on the microstructure and properties of joints were studied.The results show that with the prolonged post-weld heat treatment time,the ferrite content in the weld and heat-affected zone was reduced,and a small amount of(Fe,Cr)23C6 was precipitated in the weld microstructure.The longer the heat treatment time,the more precipitation phase,the mother The amount of precipitates in the material microstructure increases with time,and the self-corrosion potential and pitting potential of the weld and the base metal gradually decrease,and the corrosion resistance decreases.At 500? and 700°C,the tensile strength decreases gradually.The tensile strength at 900? was basically unchanged with the prolongation of heat treatment time.The fracture location occurs in the heat affected zone,and the fracture mechanism of the tensile fracture was micro-floating fracture.After 900? heat treatment after welding,the weld and base metal have the best corrosion resistance,the lowest corrosion resistance at 700?,and the lowest tensile strength and yield strength at 700?.