The hardening and embrittlement of reactor pressure vessel steels has been investigated for many years. Nowadays, a consensus is reached assuming a two-component hardening model of copper-enriched clusters and matrix damage. Nevertheless, despite being the subject of significant research efforts, it is still a debatable question, whether a linear or quadratic superposition law is appropriate. The inaccuracy of either choice might be the effect of the existence of different populations of defects, such as loops, decorated interstitial and vacancy clusters, as every defect contributes to the hardening in a particular way. In this work, a correlation on model alloys is attempted between experimental results on microstructure found by different complementary techniques and a theoretical prediction of the hardening, where each defect is defined by a specific pinning strength. It is found that loops are very strong defects, but due to their low concentration, they only play a minor role in the hardening itself. For the precipitates, the contrary is found, although they are quite soft (due to their very low sizes), they still play the dominant role in the hardening due to their high density. Vacancy clusters are important for the formation of the former two defects, but they will play almost no role in the hardening by themselves.

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