Studies On The Fatigue Property Of High Strength Steel10Ni5CrMoV

High strength steel10Ni5CrMoV has been widely used in ship manufacturing industry because of its superior material mechanics performance which can satisfy the strength design requirement of many marine equipments. In addition, in the process of diving and floating, the submarine dive will suffer from cyclic load, which requires that the pressure hull structure has the ability to resist the corresponding static load and dynamic load, so the study on the fatigue properties and simulation of fatigue life have been a significant way in modern society.This thesis obtains fatigue data by using fatigue experiments, i.e. small size smooth circular cross section specimens under axial tension test, large size coarse rectangular cross section under cantilever bending test and triaxial fatigue loading test in actual situation. Patran finite element method (FEM) software has been applied to calculate the fatigue life of T-shape weld specimens, respectively corresponding to the longitudinal force, lateral force, circumferential force and biaxial loading. In addition, the fatigue properties of the T-shape welding joint of low alloy steel10Ni5CrMoV has been studied using metallographic analysis, hardness measurement, indentation test, scratch test and fracture morphology test Utilizing optical microscope, scanning electron microscope (SEM), the organization, structure and fatigue properties of high strength steel10Ni5CrMoV low alloy welding joint was analyzed in detail. The research of high strength steel material provides guidance for optimization of marine structural design and improvement of heat treatment process.The results show that the organization of10Ni5CrMoV steel is mainly tempering sorbite, its yield strength is835MPa, tensile strength is875MPa and young’s modulus is290GPa. The welding joint consists of mainly tempered sorbite with three distinguishable regions, i.e. the base metal, heat-affected zone and the weld metal. The hardness test shows that the heat-affected zone has the highest hardness, while the heat-affected zone has the lowest plasticity in the scratch test Ductile facture was confirmed by the typical dimple structures presented on the surface. Voids and inclusions were also found in the welding joint, serving as the crack nucleation sites. Crack propagation path was determined by both the local microstructure and the macroscopic stress states. Crack started in the weld zone owing to stress concentration effect and then propagated along the interface between the weld metal and heat affected zone, which was greatly influenced by microstructure and the external force. Finally crack got through the heat affected zone and propagated within the base metal until it reached failure in the end. The fatigue life was more sensitive to stress concentration, and the simulation method was used to calculate biaxial fatigue life of welding toe, which has a decent agreement with the fatigue data. Therefore, improving the heat treatment process and optimizing the geometry of the welding joint will be the key to increasing the fatigue life of low alloy high strength steel10Ni5CrMoV.