Abstract
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.
Highlights
Low-alloy steels subjected to irradiation by high-energy neutrons exhibit mechanical hardening, due to the formation of radiation-induced nanoscale defects such as Cu-rich precipitates, solute-vacancy clusters, dislocation loops.1 The irradiation embrittlement for reactor pressure vessel (RPV) steels is currently evaluated as a ductile-brittle transition temperature shift obtained by a destructive Charpy impact test
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
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
Summary
Low-alloy steels subjected to irradiation by high-energy neutrons exhibit mechanical hardening, due to the formation of radiation-induced nanoscale defects such as Cu-rich precipitates, solute-vacancy clusters, dislocation loops. The irradiation embrittlement for reactor pressure vessel (RPV) steels is currently evaluated as a ductile-brittle transition temperature shift obtained by a destructive Charpy impact test. The development of non-destructive evaluation (NDE) method is one of the solutions, because the integrity assessment of RPVs can be done semi-permanently using the same irradiated Charpy specimens. While an increase of a major-loop coercivity, which depends on chemical compositions and neutron fluence, was observed, the coercivity was found to be strongly affected by the recovery.. While an increase of a major-loop coercivity, which depends on chemical compositions and neutron fluence, was observed, the coercivity was found to be strongly affected by the recovery.3 This results in the appearance of a local maximum in the neutron fluence dependence of coercivity. Such competing microstructural change makes it difficult to precisely evaluate effects of nanoscale defects on magnetic hysteresis properties.
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