Fatigue crack growth behavior in weld-repaired high-strength low-alloy steel

Fatigue crack growth properties and Vickers micro-hardness of a weld-repaired high-strength low-alloy steel, known for high strength, low carbon, excellent notch toughness and good weldability and formability, have been studied under the following conditions: as-received high-strength low-alloy, weld-repaired high-strength low-alloy without buffer layer, and weld-repaired high-strength low-alloy with various thickness buffer layers. Those conditions are examined to determine the respective fatigue crack growth behaviors and Vickers hardness distribution, and the effects of different weld-repaired conditions on fatigue characterizations and microscopic features of the fracture and fatigue surface. The extended-compact tension specimen geometry is adopted in this study for all tests. Paris fatigue crack growth curves and the hardness distribution across weld metal, buffer layer and parent metal has been measured together with the relevant scanning electron microscope observations along the fatigue crack growth path, with special attention at and around the interfaces between the weld metal, buffer layer and parent metal. The results show the presence of the BL of a moderate thickness has a significant influence on the fatigue crack growth behavior in the heat-affected zone and around the interface between buffer layer and parent metal. The fatigue resistance of the selected high-strength low-alloy + buffer layer + weld metal tri-metal system is higher than that of the high-strength low-alloy + weld metal bi-metal system.