Abstract
With the increase demand in high-strength steel members, high-strength steel bolts are needed for high-strength steel structure connections to provide matching tensile strength and shear strength. With the further increasing of bolt steel strength from grade 10.9 to 12.9, Hydrogen-Induced Delayed Fracture (HIDF) may become the major concern for the application of grade 12.9 high strength steel bolts in steel constructions. The HIDF resistance of grade 12.9 42CrMo high strength bolt was investigated in comparison with 20MnTiB steel for grade 10.9 bolt by means of constant load test, and analyses of fracture surface morphology and thermal desorption spectroscopy. It is found that the activation energies of the hydrogen traps of grade 12.9 42CrMo steel and grade 10.9 20MnTiB steel are very close to each other, indicating that the hydrogen traps of the two types of steel are of the same type. Because the HIDF resistance of grade 12.9 42CrMo steel is inferior to the grade 10.9 20MnTiB steel, it is not safe to simply extend current steel structure design code to include the design of grade 12.9 bolt connection. To achieve the same service life as grade 10.9 bolts, the prestress reduction factor is recommended for grade 12.9 42CrMo steel bolts.
Published Version
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