Fracture Failure Analysis on 20MnTiB Steel High-Strength Bolt Used in Bridges

Abstract

The fracture failure of 20MnTiB steel high-strength bolts in some bridges occurred. To reveal the reason for the fracture failure of the high-strength bolts, macroscopic analysis, chemical analysis, phase analysis, microscopic analysis, and metallographic analysis were carried out on one of the failed high-strength bolts. The results show that the corrosion products on the fracture surface of the failed high-strength bolt are mainly composed of SiO2, Fe2O3, and Al2O3 and contain the elements S and Cl by energy spectrum analysis. The fracture analysis of the failed high-strength bolt shows that it had two crack sources, one was outward expansion caused by the notch, and the final fracture turned out tongue pattern, while the other was outward expansion in the form of branches, and the final fracture turned out intergranular fracture morphology. It can be deduced that the main cause of the high-strength bolt fracture is machining defects and stress corrosion.