鋼材溶接継手の疲労強度に及ぼす強ショットピーニング清掃および溶融亜鉛めっきの影響

抄録

The soiling of the slag, spatter and the fume etc which come in contact with the steel sheet surface with welding cleaned making use of the steel sphere shot material of large particle diameter, high projection pressure with peening processing strongly (below, calling this strong peening cleaning). In this research, the cleaning state of the soiling with welding and improvement of fatigue strength of the hot galvanized welded joint was inspected, when surface of SM490A welded joint was cleaned with strong peening cleaning.
The following experimental results were obtained:
1) The fatigue limit of smooth base metal which did strong peening cleaning with about 320MPa was high value remarkably in comparison with smooth base metal with about 245MPa.
2) The fatigue limit of welded joint which did strong peening cleaning with about 300MPa was high value remarkably in comparison with as welded joint with about 170MPa.
3) The strong peening cleaning was high efficiency and cleaning state was satisfactory remarkably.
4) The cause of remarkable rise of fatigue limit (300MPa) of welded joint which did strong peening cleaning was because in fatigue limit (about 170MPa, 57%) of as welded joint, the improvement effect (about 130MPa, 43%) with peening cleaning was joined. It was considered that improvement effects were rise (about 68MPa, 23%) of hardness of the weld toe, relief (about 43MPa, 14%) of stress concentration, increase (about 136MP, 45%) of compressive residual stress and the decrease (about—96MPa, —32%) by increase of surface roughness.
5) The fatigue strength of hot galvanized welded joint decreased remarkably. This was thought as the thing due to the decrease (about HV40) of hardness of the surface, the decrease (about—188MPa) of compressive residual stress and the influence of many factors which was accompanied hot galvanizing.