フェライト系ステンレス鋼SUS444溶接継手の疲労挙動

抄録

Fatigue behavior of welded joints was studied on a ferritic stainless steel, SUS 444. Plate specimens with weld zone located at the center of gauge section were used for fatigue strength evaluation and two types of CT specimens were employed for crack propagation tests. The fatigue strength of the welded specimens decreased remarkably compared with that of the base metal. Multiple cracks initiated at the toe of weld, then grew and coalesced, leading to final failure. In order to discuss causes of the reduction of fatigue strength in the welded specimens, additional fatigue tests were performed using the annealed specimens and the specimens whose reinforcement of weld was completely removed. The former specimens showed only a slight increase of fatigue strength compared with the welded specimens, while the latter specimens exhibited nearly the same fatigue strength as the base metal. Based on these results, it was concluded that the effect of residual stress was relatively small and thus the significant decrease of fatigue strength in the welded specimens was attributed to the stress concentration resulting from the geometry of the reinforcement of weld. Furthermore, it was found that the crack propagation resistance of HAZ (Heat Affected Zone) and weld metal was higher than that of the base metal due to higher crack closure level.