Weldability of steel used in an aged bridge

A series of experiments was performed to investigate the weldability of steel used in an aged bridge. A steel material used in an aged railway bridge constructed in 1912 was extracted for this investigation. The chemical compositions of this steel were suitable for welding. However, the aged steel contained much sulfur. Cruciform welded joints were fabricated with this aged steel. Welding defects or cracks were not observed in the joints. The Vickers hardness test on the welded part did not confirm extreme hardening or softening. After yielding by the static tensile test, the cruciform joints were fractured at the welded parts. One of the specimens was fractured in the middle of the thickness of the aged steel. The Sulfur contained in the aged steel might cause this type of fracture. The results show that there may be a risk of brittle fracture not only from the welded part but also from the base metal. The chemical compositions of aged steel must be analyzed when repair welding is applied to the steel.