MAGNETIC INVESTIGATION ON THERMALLY AGED PRESSURE VESSEL STEELS

Satoru Kobayashi - Hiroki Sato - Taku Iwawaki - Takuya Yamamoto - Doug Klingensmith -

   Aging effect at 290 and 500°C on magnetic hysteresis property on nuclear reactor pressure vessel (NRPV) steels and Fe model al-loys for times up to 6780 hours has been investigated to understand mechanism of magnetic property changes under neutron irra-diation at the operating temperature of 290°C. While a significant change of coercivity was not detected for samples aged at 290°C, a steady increase after aging at 500°C was observed for NRPV steels, reflecting the formation of Cu-rich precipitates. On the other hand, coercivity for Fe model alloys aged at 500°C exhibits an abrupt decrease just after aging and the decrease was 20-30% of that of as-received samples. The results were explained as due to the formation of Cu-rich precipitates and recovery, but the latter has the dominant effect for Fe model alloys due to their ferritic microstructure. The possible effect of relaxation of lattice strain due to dissolved Ni under irradiation was discussed.

Keywords: magnetic hysteresis, nuclear reactor materials, thermal aging, precipitate, recovery, nondestructive evaluation

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