The segregation of impurity or solute atoms to grain boundaries as well as phase interfaces can either improve or degrade the chemical, physical and mechanical properties of alloys. This phenomenon has been studied widely for iron based alloys, and the analysis method by an atom probe tomography (APT) is a powerful tool for better understanding this problem. The resulting composition changes of grain boundaries and phase interfaces, as well as the precipitation of Cu-rich nanophases, are frequently associated with the phenomenon of embrittlement in ferritic reactor pressure vessel (RPV) steels. The present work was carried out to study the segregation of impurity or solute atoms to grain boundaries as well as phase interfaces in a RPV model steel with higher content of Cu (0.53%, atomic fraction) than commercially available one. The RPV model steel was prepared by vacuum induction melting. The specimens were further heat treated by water quenching at 880 ¢ for 30 min and tempering at 660 ¢ for 10 h, and finally aged at 370 ¢ for 3000 h. The results show

Reactor pressure vessel (RPV) is nonreplaceable component for the pressurized water reactor (PWR) in the nuclear power plants. RPVs are usually made of low alloy ferritic steels and A508-III steel is one type of these materials. After long-term service under the neutron irradiation, the ductile-to-brittle transition temperature (DBTT) of the RPV steel, which is the main parameter used to measure the degree of the embrittlement, will shift towards higher temperature. This phenomenon is termed irradiation-induced embrittlement, and it is a main factor to affect the operation safety and the lifetime of nuclear power plants. It is realized that the irradiation-induced embrittlement is mainly attributed to the precipitation of Cu-rich nanophases with a high number density. The precipitation process of Cu-rich nanophases can be well characterized by an atom probe tomography (APT) analysis for their size, composition and number density, and the Cu-rich nanophases obtained by the APT analysis are usually termed Cu-rich clusters. It is worthwhile to investigate the precipitation process of Cu-rich clusters by thermal aging for better understanding the mechanism of embrittlement. In order to accelerate the precipitation of Cu-rich clusters, experiment was performed by a RPV model steel containing higher Cu content than commercially available A508-III steel. RPV model steel was prepared by vacuum induction melting with higher content of Cu (0.6%, mass fraction). The specimens

Reactor pressure vessels (RPVs) are usually made of low alloy ferritic steels, among which A508-III steel is a typical one. The long-term neutron irradiation can induce the embrittlement of RPV steels, and the embrittlement may lead to a reduction of the RPV service life. Generally, this behavior of the embrittlement is well established and is typically assessed by the increase in the ductile-to-brittle transition temperature (DBTT) of the RPV steels. For many years, extensive studies have revealed that irradiation-induced ultrafine Cu-rich clusters (CRCs) play an important role and CRCs with high number density cause hardening and embrittlement of the RPV steels. In order to investigate the effect of the precipitation of CRCs on DBTT of RPV steels by thermal aging, it is necessary to increase the Cu content in RPV steel. A 40 kg ingot of RPV simulated steel based on the composition of A508-III steel with higher Cu content (0.6% in mass fraction) was prepared by vacuum induction melting, and it was forged and hot rolled to a plate with 7 mm in thickness. Specimens with a dimension of 7 mm×12 mm ×60 mm were cut from the hot-rolled plate. The heat treatment routes of the specimens consists of a soaking at 880 ¤ for 0.5 h, a water quenching, a tempering at 660 ¤ for 10 h, and a final aging at 370 ¤ for various times. The effect of the precipitation of CRCs on the *