提高了Cu含量的核反应堆压力容器(RPV)模拟钢经过880 ℃水淬和660 ℃调质处理后, 在370℃时效6000 h, 利用HRTEM, EDS和原子探针层析(APT)方法研究了纳米富Cu相的析出过程和晶体结构演化. 观察到Cu原子在α-Fe基体的{110}晶面上以3层为周期发生偏聚, 并产生了很大的内应力使晶格发生畸变, 这是富Cu相析出时的形核过程; 随着Cu含量的增加和富Cu区的扩大, 内应力也随着增大, 富Cu区沿着α-Fe基体的\{110\}晶面发生切变, 形成了ABC/BCA/CAB/ABC排列的多孪晶9R结构; Cu含量继续增加, 富Cu相最终转变为fcc结构. 富Cu相的尺寸在1-8 nm范围内, 数量密度为0.71×1023 m-3. 富Cu相中还含有3%-8%(质量分数)的Ni和Mn, 并且在相界面上发生偏聚, 从而抑制了富Cu相的长大.
The crystal structure of Cu-rich nanophase in reactor pressure vessel (RPV) model steel was investigated by means of HRTEM, EDS and APT methods. RPV model steel was prepared by vacuum induction furnace melting with higher content of Cu (0.6%, mass fraction). The ingot about 40 kg in 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 ℃ for 0.5 h water quenching and 660 ℃ for 10 h tempering, and finally aged at 370 ℃ for 6000 h. It was observed that the Cu atoms segregated on {110} planes of α-Fe matrix in a period every three layers and the distortion of crystal lattice was induced by inner stress produced by the segregation of Cu atoms during the nucleation of the precipitation of Cu-rich nanophase. The inner stress in Cu-rich regions enhanced with the increase of Cu concentration as well as the enlargement in size. It was also observed that the Cu-rich regions underwent a transformation from bcc structure to 9R structure with twins by means of a shear along the {110} plane of α-Fe matrix. Finally, the Cu-rich clusters transformed to fcc structure with further increase of Cu content. The results obtained by APT analysis show that the equivalent diameter and the number density of Cu-rich clusters are about 1-8 nm and 0.71×1023 m-3, respectively. The content of 3%-8% Ni and Mn within the Cu-rich clusters was detected. It is suggested that the growth of Cu-rich clusters was restrained by the segregation of Ni and Mn atoms on the boundaries around the Cu-rich clusters.
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