Research On Fatigue Ability Of 10Ni5CrMoV Steel Joints Welding By Austinite Consumables

10Ni5Cr Mo V steel developed by our country is a kind of quenched and tempered steel with high strength and high toughness, and its yield stress is 785 MPa. In order to avoid welding cold crack, austenitic electrode 0Cr18Ni24Mo6 N is used for welding large rigidity structure. Fatigue failure is focused on for causing ship structure failure in ship design and building. F-A-F joint of 10Ni5 Cr Mo V steel welded by 0Cr18Ni24Mo6 N is widely used in heterogeneity joint, but its fatigue property has not been studied. The calculation of weld toe stress and strain, cyclic stress-strain constitutive relationship, fatigue property of F-A-F joint under plane stress and plane strain condition are investigated in this thesis.Cyclic stress-strain curves of 10Ni5 Cr Mo V base metal and 0Cr18Ni24Mo6 N weld metal under series of strain amplitude are measured. Their cyclic stress-strain properties are revealed. The yield stress of material is significantly reduced by cyclic plastic strain. The materials have no obvious cyclic hardening and softening at constant strain amplitude. The stress-strain curves of stress during increasing period and decreasing period are rotational symmetry at the same strain amplitude. The yield stress and apparent elastic modulus are both linearly decreased with the increasing strain amplitude. Yield stress and plastic strain meet single logarithmic relationship in cyclic plastic deformation period. The single logarithmic strain-hardening constitutive equation is proposed to describe the cyclic stress-strain. The constitutive equations of 10Ni5 Cr Mo V base metal and 0Cr18Ni24Mo6 N weld metal under cyclic plastic strain condition based on linear strain-hardening model and power strain-hardening model are also provided.The cyclic stress-strain property of F-A-F joint under plane stress is analyzed through numerical simulation and fatigue experiment. The S-N curve and fatigue property of F-A-F joint with 10Ni5 Cr Mo V and 0Cr18Ni24Mo6 N under plane stress are obtained. The crack initiation life of F-A-F joint is higher than that of ferrite joint with the same strength under the same fatigue load. High proportion of total fracture life, which is over 70%, is taken by crack initiation life. The strain parameters nearby austenitic weld metal are higher than those of ferrite weld metal, but the fatigue cracks are all emerged at weld toe and propagated to base metal which is perpendicular to load direction.The cyclic stress-strain property of F-A-F joint under plane strain is analyzed through numerical simulation and fatigue experiment. The fatigue property of F-A-F joint with 10Ni5 Cr Mo V and 0Cr18Ni24Mo6 N under plane strain condition is obtained. Stress reversal effect can be caused by stress concentration and localized plastic deformation. Stress at weld toe is cyclic stretch and compression which can result in initial crack and its propagation at weld toe. For F-A-F joint, peak stress and strain at weld toe nearby austenitic weld metal are higher than those of ferrite weld metal. Therefore, the fatigue crack occurs at the weld toe which is near to the austenitic weld metal, and the crack grows a short distance along the fusion line, then it would continue to propagate in base metal.Calculation equations of peak stress and valley stress at weld toe under different cyclic load conditions are established concerning the initial residual stress based on linear strain-hardening model, power strain-hardening model and single logarithmic strain-hardening model. Stress concentration factor equation of heterogeneity joint is also provided due to the material difference based on the numerical simulation result.The cyclic stress-strain constitutive relationship of 10Ni5 Cr Mo V and 0Cr18Ni24Mo6 N, fatigue property of 10Ni5 CrMo V joint welded by austenitic metal under plane stress and plane strain conditions, calculation equations of stress and strain at weld toe under plane stress condition considering residual stress, stress concentration factor equation of heterogeneity joint considering material difference can provide technical support for reliability design of 10Ni5 Cr Mo V joint.