Experimental Investigation of Hydrogen Embrittlement in Post-Fire Q690 Weldments

The evaluation of the mechanical properties of post-fire high-strength steel welds, particularly for secondary applications in medium and large infrastructure, is of critical importance in engineering. This study investigates Q690 high-strength steel welds subjected to heat treatment at 300°C, 500°C, 700°C, and 800°C for 20 minutes, followed by air cooling. Electrochemical hydrogen charging, uniaxial tensile testing, and fracture morphology analysis were employed to examine the mechanical properties of these welded components after fire exposure. The effects of hydrogen embrittlement on the mechanical properties and fracture modes of Q690 welds were analyzed, and a hydrogen embrittlement sensitivity index for the welding joints was proposed. The results of the study show that the heat treatment temperature has a significant effect on the hydrogen embrittlement susceptibility of welded structural components. Higher heat treatment temperatures and longer hydrogen charging times lead to a decrease in the mechanical properties of the material, which is characterised by a flatter and smoother macroscopic fracture surface, while the microscopic fracture pattern is characterised by micro-voids. Hydrogen-induced deformation leads to the accumulation of structural defects, such as micro-inhomogeneities and micro-voids, due to increased hydrogen concentrations. Consequently, the material’s resistance to brittle failure is diminished.