We report results of measurements of first-order reversal curves (FORCs) for neutron irradiated reactor pressure vessel steels to seek their possible application to a nondestructive evaluation of the irradiation hardening. We find a peak position of the FORC distribution, which is the second derivative of measured FORCs, shifts towards zero field after neutron irradiation, associated with the narrowing of the peak width. The observations indicate the progress of the magnetic softening and magnetic homogeneity under neutron irradiation. The present investigations demonstrate that FORCs can offer additional information on microstructural changes due to neutron irradiation, which can not be obtained by a conventional hysteresis method.
