Nondestructive Evaluation of Plastic Deformation in Reduced Activation Ferritic/Martensitic Steels for Structure of Fusion Reactors

Reduced Activation Ferritic/Martensitic (RAFM) steel is considered to be a candidate structural material for future Tokamak fusion nuclear reactors. The plastic deformation may occur during the operation of the reactor for reason of unexpected loads. Therefore, a reliable non-destructive evaluation (NDE) of RAFM steel is needed. In this study, magnetic NDE methods such as magnetic Barkhausen noise (MBN), magnetic incremental permeability (MIP) and magnetic flux leakage (MFL) method have been applied to evaluate the residual plastic strains in RAFM steel to ensure the structural integrity after an unexpected giant loading process. The study shows that the MBN signals and the amplitude of the high harmonic components of the MFL signals decrease regularly with the increasing residual strain. The shape of MIP butterfly trajectory also changes evidently in range of small plastic deformation. The experimental results reveal that the MFL method is the most suitable way in the three magnetic NDE methods for measurement of plastic strain in the RAFM steels.