Effect of long-term thermal aging on magnetic property in reactor pressure vessel steels

Effect of long-term thermal aging at 290 and 500 °C on magnetic hysteresis property in reactor pressure vessel steels and simple model alloys have been investigated for times up to 8800 h. While Vickers hardness is insensitive to thermal aging at both temperatures, coercivity generally exhibits a slight decrease after aging at 290 °C. In particular, at a higher temperature of 500 °C a steady increase of coercivity was observed for reactor pressure vessel steels, whereas coercivity for simple model alloys exhibits an abrupt drop just after aging and the decrease was 20–30% of that before aging. The results were interpreted by the thermally-assisted formation of Cu-rich precipitates and recovery, but the latter has the dominant effect for simple model alloys because of their ferritic microstructure. The possible effect of relaxation of lattice strain created by dissolved interstitial atoms during neutron irradiation is proposed.