Abstract: A bolt of 05Cr17Ni4Cu4Nb high-strength stainless steel fractured during fastening. In this paper, the fracture morphology, metallographic structure, chemical composition and mechanical properties of the broken bolt were tested and observed by scanning electron microscope, optical microscope, inductively coupled plasma spectrometer, microhardness tester, and tensile tester. And the fracture mechanism was analyzed. The results indicate that the fracture of the bolt is intergranular brittle fracture. Both the chemical composition and mechanical properties of the bolt meet the requirements, but the microstructure is coarse and contains excessive δ-ferrite. Improper control of heating temperature during hot upsetting and solid solution processes led to local higher temperature. The transverse toughness of the bolt decreased due to excessive δ-ferrite, leading to a decrease in its shear resistance and fracture under a large torsional torque.