Development Of Self-shielded Flux Cored Wire For FV520(B) Steel And Microstructure And Performance Of Welded Joint

At present,centrifugal fans are used in the metallurgical,power,chemical and other important areas of national conomy.FV520(B)martensite stainless steel used for the manufacture of draught fan with its excellent comprehensive performance.But fracture failure often happens to the impeller produced by it because of short toughness of welded joint and unsuitable technology for heating processing.The existing welding of FTV520(B)martensite stainless totor adopts imported electrode in China,which has eligible quality but high cost.The domestic welding materials has low cost,while the performance is poor.To meet the performance requirements fur welded joint,reduce the production cost of welding material and break the foreign monopoly,this paper based on microalloying theory,designed experiment and optimized wire formula by homogeneous design and regression analysis,tested and analyzed by metallographic observation,the mechanical property test,fracture scanning,and energy spectrum analysis,etc.The self-shielded flux cored wire that matches FV520(B)was successfully researched eventually.Meanwhile,the microstructure and property of researched flux cored wire were deeply analyzed.The results show that by the methods of uniform design and the regression analysis,ullimately determine the optimal welding process for each component content with Rutile 28-32%,Zircon sand 5-8%,Quartz 2-5%,Feldspar 8-10%,sodium carbonate 2-5%,Aluminium oxide 2-5%,Aluminium magnesium alloy 8-12%,Ferromanganese 6-8%,Chromium powder 16-20%,Nickel powder of 6-8%.Niobium iron 2-5%,Molybdenum powder 2-6%.After welding and heat treatment,both the organization of weld and HAZ FV520(B)martensite stainless steel are tempered sorbite(S)+ lath martensite(M)+ residual austenite(A')+secondary precipitated phase,and the secondary precipitated phase mainly about NbC,Mo2C3,Cr23C6,Cr7C3,Ti(C,N),etc.In the high temperature tempering,a small amount of reverse austenite appeared in the organization.FV520(B)precipitation hardening stainless steel mainly contains martensite phase can improve the toughness of deposited metal by transiting moderate alloying elements like Mo,Nb,Ni,Ti,B and Re,and obtain an excellent performance.The fracture analysis shows that 8-3#wire has best toughness,and the fracture mechanism is complex fracture with toughening nest and cleavage.The inclusions which exists in toughening and torn edges at the bottom of the tip with regular tetrahedron and irregular topography,mainly contains the elements such as Ti,Al,Cr,Si.The particles are carbide of Ti,Mn,Cr,and oxide of Al,Si,and have adverse effects for impact toughness of the joint.The corrosion resistance of welding joint of FV520(B)martensite stainless steel in the 10%H2SO4 solution all greater than the parent metal.Analysis shows that the improve of alloy elements such as Cr,Ni can significantly increases the corrosion resistance of welding joint,and the transition of alloy elements such as Nb,Ti to the weld through a wire also increase the corrosion resistance of welding joint.