Abstract
Neutron irradiation of low-copper reactor pressure vessel steels containing manganese and nickel gives rise to microstructural changes and a deterioration of mechanical properties. This deterioration apparently progresses slower than in steels containing more than ∼0.1 wt% Cu. An acceleration of this process after the accumulation of a threshold fluence caused by the so-called late blooming phases is a matter of debate. We report results of small-angle neutron scattering experiments and tensile tests for two low-Cu model RPV steels irradiated at 255°C. Motivation is given for the use of the integrated magnetic scattering as a microstructural parameter combining the volume fraction and magnetic contrast of nanometer-sized irradiation-induced features. The results indicate one of the rare cases of acceleration of both a change of a microstructural parameter and a yield stress increase. The issues of the nature of the irradiation-induced features, the role of phosphorus, and the observed strong correlation of integrated magnetic scattering and yield stress increase are addressed.
Acknowledgement
The SANS experiment was performed on the spectrometer D11 of ILL Grenoble with the kind assistance of Charles Dewhurst.