4388 - FATIGUE CRACK PROPAGATION CHARACTERISTICS OF WELDED JOINTS IN A 444 STAINLESS STEEL

This paper describes the fatigue crack propagation (FCP) behavior for large cracks of a ferritic stainless steel welded joints. FCP experiments were performed using electro-hydraulic fatigue testing machine in laboratory air and in 3%NaCl aqueous solution. Three types of welded CT specimens, the specimens in which the starter notch was introduced perpendicular to the weld line, within HAZ (Heat Affected Zone) and within the weld metal, were evaluated. In laboratory air, when the crack propagated normal to the weld line, FCP behavior was rather complicated and FCP rates decreased temporarily as it reached HAZ and then increased with crack propagation within HAZ. When the crack propagated within HAZ and the weld metal parallel to the weld line, FCP rates were significantly lower than those of the base metal in the entire ∆K region. After allowing for crack closure, however, the FCP data of all the welded specimens became similar and agreed with those of the base metal. In 3%NaCl aqueous solution, the FCP rates of all the welded specimens were still enhanced at high ∆Keff regime, where some intergranular fracture and quasi-cleavage fracture were seen, which was due to an environmental effect.