繰返し応力下における磁壁のピン止め効果緩和に関する検討

抄録

A magnetic Non-Destructive Inspection (NDI) method based on measurement of the magnetic flux leakage near the surface has been studied for inspection of carbon steel pipes used in various plants. However, in an actual plant, stress fluctuations caused by changes in the temperature and internal pressure of the fluid passing through the pipes may affect the residual magnetization state and prevent accurate inspection. In this study, we applied cyclic stress to pre-magnetized STPG370 carbon steel and measured the change of the magnetization state as the change of the magnetic field near the surface of the specimen to investigate the relaxation of the pinning effect of the magnetic domain wall under cyclic stress. As a result, it is shown that under the environmental magnetic field (same or opposite direction to the specimen magnetization), the magnetization (or corresponding magnetic field near the specimen surface) of the specimen decreases significantly after the first few cycles of stress loading and the magnetization state approaches the neutral magnetization state. And it is also found that the magnetization gradually decreases further with higher cycles of stress loading and under the opposite magnetic field the sign of magnetization is finally reversed.