Austenitic stainless steel has been extensively used in nuclear power plants (NPP). The nondestructive Testing (NDT) of its mechanical damage at pre-crack state is very important for the safety assessment of a NPP. Aiming at to develop a new NDT method for inspecting mechanical damage before the initiation of macro cracks, the correlation between the natural magnetization and the mechanical damage is experimentally investigated for a typical austenitic stainless steel - SUS304. In the experiments, simple tensile loads were applied to lateral notch specimens to generate states of different plastic damages, and the corresponding natural magnetic field and residual strain distribution were measured after each loading cycle. The distribution of natural magnetization was analyzed based on the measured magnetic field signals in view of the principle of the metal magnetic memory phenomenon, and the dependence of the magnetization on the mechanical damage was discussed. The experimental results reveal that there is a good possibility to detect mechanical damages by measuring the natural magnetic field.

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