Abstract: The O-shaped hole of the stainless steel 05Cr17Ni4Cu4Nb tie rod OU type joint used in a bridge project was broken during service. In order to find out the cause of the failure, the chemical composition, macroscopic fracture, microstructure, and mechanical properties were tested and analyzed. The results show that the chemical composition of the joint is in accordance with the standard of 05Cr17Ni4Cu4Nb in GB/T 1220—2007, the specified non-proportional elongation strength and tensile strength reaches the technical requirement of the steel aged at 480 ℃. However, the elongation after break and percentage reduction of area are lower than the requirements, revealing that the material is with poor plasticity, which should be due to the precipitated δ ferrite resulted from a high solution treatment temperature. Therefore, the overload brittle fracture of the joint occurs which is caused by its high surface notch sensitivity.

Key words: stainless steel, tie rod, joint, fracture, failure analysis