| With the rapid development of the power industry,the emergence of high-parameter,large-capacity generating units has brought about higher requirements for high-temperature creep and stress corrosion resistance of steel pipe materials.The T91/P91 martensitic heat-resistant steel,with its high temperature durability strength,thermal stability and high temperature creep resistance capability,has been more widely used for high temperature superheaters,reheaters and main steam pipes of power station boilers.Compared with 12Cr1 MoV steel,the carbon content of T91 steel decreased by 20%? The composition of these two kinds of steel are also very different,so the joint structure will be uneven when welding there will be many problems.This subject researches the TIG welding butt joints of T91 steel and 12Cr1 MoV steel pipe,conducts hot corrosion research on heterogeneous heat-resisting steel welded joint under simulated conditions,analyzes the corrosion behavior of joints in various areas,and observes the corrosion products at the same time and gives some guidance for production process.Using different welding parameters of argon arc welding,ER55-B2-MnV welding material was selected to weld T91 and 12Cr1 MoV heat-resisting steel pipes with a diameter of 5mm.The mechanical properties of the welded test tube were tested and the macroscopic formation of the welded joints and the microstructures of the various regions were observed.The microhardness was tested.A 3.5% NaCl solution soak and electrochemical corrosion experiments were performed on the dissimilar steel butt joints.Through the soaking experiment and electrochemical corrosion experiment,the corrosion resistance of dissimilar steel welded joints welded by different welding processes was studied.Experimental studies show that: different process parameters have a significant effect on weld formation and weld force performance.The forming under the currents of 100 A and 120 A are significantly better than those of 140 A.The bestwelding current is 120 A through mechanical testing.The microstructures of the base metal,heat-affected zone and weld are all different.The microstructure of the T91 base metal is martensite.The microstructure of the 12Cr1 MoV base metal is pearlite and ferrite.The different of the heat effected zone(HAZ)and weld is obvious,and the microstructure of the weld zone are not uniform.Due to the presence of hardened microstructures,the hardness of the heat-affected zone of the T91 side is the highest.The 12Cr1 MoV base metal has the lowest hardness because its microstructure are pearlite and ferrite.The weld formation and microstructure affect the corrosion resistance.The weld zone is coarse martensite and the structure is not uniform,resulting in non-corrosion resistance;the microstructure of the T91 side heat affected zone is not uniform,leading to corrosion resistance worse than T91 of base material;T91 base metal is martensite,while 12Cr1 MoV is pearlite and ferrite.Martensite is more corrosion resistant than pearlite,so T91 base metal has good corrosion resistance.It can be known from the immersion corrosion and electrochemical corrosion tests that the welded joints of 120 A are well formed and their corrosion resistance is good.The corrosion resistance of 100 A welded joints is worse than that of 120 A.The welded joints of 140 A are poorly formed and their corrosion resistance is also poor.In the process of stress corrosion test using constant deformation method,some elastic deformation in the sample is transformed into plastic deformation.With the progress of experiment,the plastic deformation is also bigger,which leads to the stress drop of the specimen,which makes the test always fail to get the crack.The plastic deformation produced by tensile test has an effect on the corrosion performance of T91/12Cr1 MoV dissimilar steel welded joint.When the plastic deformation produced by tensile is 5%,the specimen is in plastic deformation stage,and the corrosion performance of the specimen is not as good as that of the UN tensile sample. |
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