APT AND EXTRACTION REPLICA CHARACTERIZATION OF Cu–RICH CLUSTERS PRECIPITATED IN PRESSURE VESSEL MODEL STEELS

Abstract

The precipitation of Cu-rich clusters in reactor pressure vessel (RPV) model steel was investigated by means of atom probe tomography (APT), extraction replica (ER) and HRTEM. RPV model steel was prepared by vacuum induction furnace melting with higher content of Cu (0.6%, mass fraction). The ingot (about 50 kg of weight) was forged and hot-rolled to 4 mm in thickness and then cut to specimens of 40 mm×30 mm. Those specimens were further heat treated by 880 /0.5 h water quenching and 660 /10 h tempering, and finally aged at 370 for different time from 1000 to 6000 h. 4% nitric acid alcohol solution was used as an etchant to extract the precipitates of Cu-rich clusters from �-Fe matrix. The results obtained by APT analysis show that the number density of Cu-rich clusters reaches 3.1×10 23 m −3 in the specimen aged at 370 for 4500 h, and the Cu content in the clusters increases rapidly during their growth from 1 nm to 5 nm. The segregation of Ni and Mn elements within and around the Cu-rich clusters was detected. The results obtained by ER, EDS