Research On Microstructure And Corrosion Properties Of Super Duplex Stainless Steel Welded Joints

The corrosion problem of the welded joints of super duplex stainless steel which are used as petrochemical equipment has received a lot of attention with its wide application.So far there have been related researches at home and abroad,the corrosion problems of super duplex stainless steel welded joints have not been solved,and this result oil and gas leakage and environmental pollution accidents occurred.In this paper,the petroleum pipe is taken as the research background,and the microstructure and corrosion behavior of super duplex stainless steel welded joints are studied.Tungsten argon arc welding with pure argon shielding gas was adopted to study the influence of welding passes on microstructure and corrosion performance.The distribution of alloying elements such as Ni,Cr and Mo and their effects on mechanical properties and corrosion resistance were investigated.The weld center has high austenite content,its corrosion rate was about 0.68 times of the weld root,and the austenite content of the cap and the root were close,but the weld cap performed better corrosive property due to the larger intragranular austenite.Austenite exhibited better corrosion resistance.The weld root was a weak area of the weld metal.The mixing zone has the fastest corrosion rate due to the presence of the heat affected zone.And HAZ precipitated a large amount of Cr₂N.After component analysis,it was found that there was obvious chromium-depleted area around it,which induced pitting germination and expanded to the surrounding ferrite phase.The effect of nitrogen addition on the microstructure and properties of the welded joints was investigated through adding 2%of nitrogen to the shielding gas.The results show that in both cases,the addition of nitrogen in the shielding gas promotes the formation of austenite,reduces the corrosion current density by an order of magnitude,and imcreses the CPT by 4-8?.Through the calculation of the Factage equilibrium phase diagram,the approximate solution heat treatment temperature range 1150-1190?can be obtained,and the optimum solution temperature 1170?can be selected according to the results of the microstructure and performance analysis.The experimental results show that the austenite content and uniformity of the welded joints are optimal at 1170?,and the protective effect of the passivation film is relatively uniform in each region,and the difference in CPT is small.