The samples for this study were taken from reactor pressure vessel (RPV) model steel having higher Cu content. The samples were divided into two sets. The first set of samples were heat treatment of 0.5 h at 880℃and quenched into water, and the second set of samples were tempered at 660℃for 10 h followed by air cooling after an initial heat treatment of 0.5 h at 880℃and quenched into water. Two sets of samples were then isothermally aged at 300℃-500℃for different times up to 6000 h. The Vickers microhardnes...