Abstract
In order to investigate characteristics of surface fatigue crack propagation from a pit shaped surface defect which frequently exists around welded joints, SS400 steel with thickness of 12mm, which has been generally used for structure members, was welded with submerged-arc butt type and machined for both surface. An initial surface defect of pit shape with the aspect ratio of 2 was made on the specimen. The initial defect was located at 5 different zones over the weldment : weld metal zone, boundary between weld metal and HAZ, HAZ, boundary between HAZ and base metal. Characteristics of surface fatigue crack propagation from the defect on each region under the same loading condition were investigated and compared.
