Effect Of Element Vanadium On The Mechanical Properties Of T91/316L Welded Joints And Corrosion Behavior Of The Weld Seam In Liquid LBE

316L/T91 dissimilar steel welded joints are widely used in the fourth generation of nuclear power development and application due to their good high temperature performance and corrosion resistance.They are ideal structural materials for accelerator driven subcritical systems(ADS).Lead-bismuth eutectic crystal(LBE)is used as coolants and spallation target materials in ADS.Dissimilar steel joints are in high temperature,high pressure,liquid LBE corrosion and other environments during service.Therefore,it has theoretical practical application value to realize high-quality welding of 316 L austenitic steel and T91 martensitic steel and to investigate effective methods for improving the welding joints' LBE corrosion resistance.And it provides a reference for the future application of nuclear power development.In order to investigate the corrosion performance of dissimilar steel joints,316L/T91 joint using TIG with four different kinds of welding wires with different vanadium content(0 wt.%,0.2 wt.%,0.4 wt.%,and 0.6 wt.%)were immersed in oxygen-saturated liquid LBE at 400°C.By analyzing and comparing the microstructure,mechanical properties,the surface morphology after corrosion and the formation of the cross-section oxide layer,the effect of vanadium on the structure,performance and LBE corrosion resistance of 316L/T91 welds was investigated.After metallographic observation and related mechanical property tests on the four groups of welded joint samples,it was found that the weld structure obtained by the four welding wires is austenite and ? ferrite.The weld structure becomes more uniform and finer with the content of vanadium in the welding wire increasing.When the content of vanadium is 0.6 wt.%,the structure is the most even and finest.In order to explore the effect of vanadium on the tensile strength of the weld,the method of prefabricated notch is used to control the fracture to occur at the seam.With the increase of vanadium,the tensile strength of the weld is increased.The fracture of the Charpy impact test is located at the weld.With the increase of the content of vanadium,the value of the impact absorption work increases and the size of the crater at the fracture increases,indicating that the impact toughness is improved.The hardness near the fusion line on the T91 side is significantly higher than other regions with using the welding wire of zero vanadium element,and there are large fluctuations.After adding vanadium,the hardness of this region decreases.The protrusion of hardness curve disappears and the hardness distribution in the weld zone tends to be horizontal when vanadium content is 0.6 wt.%.Four groups of weld samples were subjected to 200 h,500h and 1000 h corrosion tests in 400?,static LBE and 400?,2.74 m/s high-speed flowing LBE respectively.Under both corrosion test conditions,corrosion pits were formed on the sample surface and ellipsoidal compounds were formed.After 1000 h,the generated compounds were connected to each other and then covered the sample matrix.Under high-speed corrosion conditions,the sample surface had "Gully" erosion marks,and part of the oxide layer fell off.EDS analysis results of the sample cross-section showed that a double-layered oxide layer was formed at the interface between the sample substrate surface and the LBE.The outer layer structure was loose,and the main elements were Fe and O,and there is a small amount of Pb and Bi infiltration.The inner structure is dense,and it has a certain protective effect on the matrix.The main constituent elements are Cr,Ni and O.The corrosion forms of static corrosion are mainly dissolution corrosion and oxidative corrosion.The Fe and Cr elements in the matrix dissolve into the liquid LBE,and the O,Pb and Bi elements in the liquid alloy diffuse into the material matrix.Under high-speed flow corrosion conditions,the LBE cause friction and makes oxide layer fall off to aggravate the corrosion of the sample.From the contrast of the thickness of the oxide layer,as the content of the vanadium element increases,the thickness of the oxide layer decreases.When the vanadium content is 0.6 wt.%,the corrosion degree of the weld sample is the weakest,and the corrosion resistance in LBE was the best.