抄録
In large welded steel structures, there are a lot of free edges cut by plasma arc cut without finishing treatment. In the surface layer of steel plate with plasma arc cut surface, the material is hardened. Therefore, we have to take care of the reduction of fatigue strength due to the local stress concentration and residual stress in the surface layer.
In this study, from a view of the present, the fatigue strength in air and in artificial seawater of five types of 490 MPa class high tensile steel plates with plasma arc cut surface were organized and evaluated comparatively. As a result, the following conclusions were obtained :
1) The surface layers of the steel plates cut by plasma arc cutting were quenched and hardened (about 500～400 HV 3N).
2) For the fatigue strength in air at 1×106 cycles, all types of tested steel plates with plasma arc cut surface or gas cut surface had the fatigue strength over about 90% of the steel plates with machined cut surface and it shows that plasma arc cutting and also gas cutting have almost no problem on the fatigue strength in air of these steel plates.
3) For some types of steel plates cut by plasma arc cutting, the fatigue strength in artificial seawater decreased obviously.
4) Under the conditions in air, the negative effect of plasma arc cutting on the fatigue strength of 490 MPa class high tensile steel plates does not need to be particularly taken into account, while under the corrosion conditions in seawater the sufficient consideration and measures for the fatigue strength of these steel plates are needed.
