高サイクル繰返し負荷を受ける炭素鋼の応力磁化効果に関する実験的検討

Abstract

A magnetic non-destructive inspection method based on measurement of the magnetic flux leakage near the material surface has been studied for carbon steel pipes used in various plants. However, in actual plants, stress fluctuations caused by changes in the temperature and internal pressure of the fluid passing through the pipes may affect the residual magnetization state due to magnetomechanical effect and prevent accurate inspection. In this paper, we applied cyclic stress to pre-magnetized STPG370 carbon steel up to 10⁷ cycles and measured the change of the magnetization state as the change of the magnetic field near the specimen surface. As a result, under the environmental magnetic field, the magnetization (or corresponding magnetic field near the specimen surface) of the specimen decreases significantly after the first few cycles of stress loading, which suggests the magnetization state approaches the anhysteretic (stable) magnetization state. Furthermore, the magnetization gradually decreases further with higher cycles of stress loading.