Stray flux effects on the magnetic hysteresis parameters in NDE of low carbon steel

The magnetic minor hysteresis loops and parameters of low carbon steel plate samples annealed at different temperatures have been measured and compared with the results of ring samples. The influences of stray flux in the fringe areas of the plate on the magnetic properties were discussed with the help of a finite element approach. It is found that the coercivity HC and the hysteresis loss WH of all of the plate samples sharply deviate from the values of the corresponding ring samples with the same applied field amplitude Ha larger than 3000 A/m. It is proposed that the fringe areas of the plate sample are magnetized by the stray flux to an irreversible state at large Ha, and the remanent fields act against the applied field in the inverse direction, resulting in the extreme increase of HC and WH. Although these parameters measured at high-applied field can reflect the microstructure changes, low field results are preferable for the practical use.