Study On Microstructure And Corrosion Resistance Of SASS 254SMo TIG Welding Joint

SASS 254 SMo has excellent corrosion resistance,high mechanical properties and high oxidation resistance because of the high contains of Cr,Ni,Mo elements,and more and more widely used in harsh corrosive environment,especially high chloride ion corrosion environment and the cost advantage is remarkable,Therefore,it becomes the important material of the seawater desalination,the flue gas desulphurization,the sewage treatment and so on,However,during the welding process,due to the complex alloy composition,the influence of the thermal cycle of the welding,will lead to the heat affected zone(HAZ)austenite grain coarsening and the second phase of precipitation,causing 254 SMo steel welded joint mechanics Performance and corrosion resistance of the decline,thereby shortening the life of the welding structure.At present,the research on 254 SMo at home and abroad is mainly focused on the welding process method,as well as the effect of solid solution aging on precipitation phase,corrosion resistance of materials and so on.However,the research on the corrosion resistance of welded joints with different heat input is rarely reported.In this paper,the heat affected zone of 254 SMo welding is simulated by GLEEBLE3800,and the actual TIG welding is carried out on this basis.The relationship between the mechanical properties and the corrosion resistance of the welded joint was studied systematically under different welding parameters.Firstly,254 SMo heat affected zone(HAZ)was simulated and the effects of heat input and cooling time t12/8 on microstructure properties the hardness and the second phase precipitation of heat affected zone(HAZ)were investigated by OM and SEM in the paper.The results indicated that with the enlargement of heat input,austenite grains coarsed and the microhardness decreased.When the heat input increased greater than 1.5kJ / mm,Sigma phase was observed along the austenite grain boundaries gradually increased,no Sigma phase was found inside the grains.Secondly,254 SMo TIG welding experiment was carried out and the influences of heat input on microstructure and mechanical properties of welded joints were studied by OM,SEM;microhardness and charpy impact in the paper.The results indicated that weld solidification mode was fully austenitic solidification.With enlargement of heat input,the toughness of the welded joint gradually deteriorates,the microhardness increases first and then decreases,which reached top at 1.56kJ/mm.When the heat input increases to 2.83KJ/mm,? phase precipitation was found in the heat affected zone.Finally,the electrochemical corrosion behavior of 254 Smo welded joints was carried out by electrochemical workstation,and the effect of heat input on the pitting corrosion resistance of the welded joint was investigated.The results indicated that when heat input was less than 2.04kJ/mm,passive current density of potentiodynamic polarization curve was relatively small,secondary passivation current is small,while broken potential relatively high,which showed compact passivation film,high self repair ability and good pitting resistance while the heat input below 2.04 k J/mm.Considering the effect of heat input properties,mechanical properties and microstructure of pitting resistance welding of super austenitic stainless steel 254 SMo,heat input between 0.97~2.04 kJ/mm was recommended in actual TIG welding production.