Study On The Relationship Between Microstructure And Corrosion Resistance Of 2205 Duplex Stainless Steel Laser Hybrid Welding Joint

2205 duplex stainless steel(DSS)is a kind of stainless steel with high strength and excellent corrosion resistance widely used in harsh environment.However,after welding,the microstructure of welded joint is very different from that of base metal,so it is important to study the relationship between microstructure and corrosion resistance of joint.In this paper,DSS2205 was welded by laser hybrid welding(LHW)(laser + MIG)with different parameters to obtain some welded joints with different microstructure.The mechanical properties and corrosion resistance of welded joints were further analyzed.The metallographic observation of welded joints shows that the austenite phase decreases gradually in the thickness direction,and harmful phases precipitated in ferrite phase,hot-affected area(HAZ)and the ?/? interface.The increase of hot input could improve the austenite content,but the total ? content generally less than 50%.The tensile test consequence showed that the strengths of joints are slightly lower than base metal.According to the fracture analysis,some ferrite phase is quasi cleavage fracture for the precipitates.The hardness test results showed that the hardness of weld metal is lower than base metal while the HAZ is higher.During the welding process,additional nickel elements are added to the weld as the wire is melted which will decrease the hardness of welded metal.Bedsides in the high temperature,the nitrogen element will have certain burning loss,which causes the solid solution enhancement to reduce.In HAZ,the growth of grain leads to the increase of hardness under the high temperature.The potentiodynamic polarization experiments indicate that the corrosion resistance of welded joints is lower than that of base metal,and weak performance area is HAZ.In addition,the pitting potential of joint is close to that of base metal but the pitting protected potential is significantly lower than base metal which means the re-passivation ability of joints is poor.The critical pitting temperature(CPT)and polarization test results showed that the CPT of joints is lower than that of base metal,and the worse the microstructure uniformity of welded joints is,the lower the CPT is.According to the pictures took by scanning electron microscope,pitting occurs have obvious difference in the weld.Pitting usually occurs in austenite phase at the region where do not have precipitations.And in other area,pitting occurs in where the precipitations are when the content of precipitations is large.The Mott-Schottky(M-S)test results in different temperatures indicate that the integrity of the passive film on welded joints surface is similar to that of base metal.Under different applied potentials,the passive film exhibits different semiconductor properties.Furthermore,at the same region of different welded joints,the higher the austenite content is,the larger the density of carrier in passive film is,and the more easily the pitting corrosion occurs.Moreover,the proper temperature can promote the growth of the passive film.The increase of temperature has no effect on the carrier density,but will improve the flat bond potential of passive film,and decrease the pitting corrosion resistance.