Fatigue crack propagation (FCP) tests have been conducted using CT specimens cut from mash seam welded joints coupled with two different steels, cold rolled low carbon steel and high tensile strength steel. FCP rate for two different directions, paralled and normal to the weld, were determined. In both directions, the FCP rates for the welded joints were considerably lower than those for the unwelded base steel regardless of the coupling of steel and slightly decreased FCP rates were seen within the weld zone in the FCP direction normal to the weld. After allowing for crack closure, the welded joints showed almost the same FCP behaviour as the base steel, indicating that the higher apparent FCP resistance were mainly due to compressive residual stress resulting from the welding. The differences in FCP behaviour between mash seam and laser welded joints are discussed on the basis of material property changes.
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