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Takeuchi, Tomoaki; Kuramoto, Akira*; Kameda, Jun*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Hasegawa, Masayuki*; Okubo, Tadakatsu*; Yoshiie, Toshimasa*; Nishiyama, Yutaka; Onizawa, Kunio
Journal of Nuclear Materials, 402(2-3), p.93 - 101, 2010/07
Times Cited Count：59 Percentile：96.15(Materials Science, Multidisciplinary)This study reports the effects of the composition and dose on microstructure evolution and hardening in high- and low-impurity A533B-1 steels neutron-irradiated in a wide range from 0.32 to 9.9 
10
n cm
(E 
1 MeV) under a constant high flux at JMTR. The early hardening was found to be caused by mainly matrix defects. The gradual hardening after middle stage of irradiation was found to be caused by the formation of Cu rich clusters (CRCs) and Mn-Ni-Si rich clusters (MNSCs), respectively, in the high- and low-impurity steels. By applying a RB model, it was found that the dislocation-pinning strength of the CRCs and MNSCs is almost the same. Moreover, the high-impurity steel subjected to the highest dose revealed the formation of MNSCs.
Takeuchi, Tomoaki; Kuramoto, Akira*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Hasegawa, Masayuki*; Yoshiie, Toshimasa*; Katsuyama, Jinya; Nishiyama, Yutaka; Onizawa, Kunio
no journal, ,
The dose dependence of the micro structural evolution and its correlation with hardening of the reactor pressure vessel (RPV) steel irradiated with neutrons is investigated. The two kinds of A533B-1 steels of different chemical compositions irradiated at JMTR with the almost same flux from 1.6 to 1.910
n cm s
and the wide range of dose from 0.32 to 9.910n cm are studied using the Vickers micro hardness, the positron annihilation, and the three-dimensional local electrode atom probe (LEAP) techniques. Results indicate that the gradual hardening of the high impurities steel from the middle to the late stage is caused by the solute nano-clusters enriched with Cu, Si, Mn, Ni, and P. It is also suggested the rapid hardening of both steels at the early stage of irradiation is caused by mainly matrix defects, especially small size vacancies and/or dislocations.
Katsuyama, Jinya; Onizawa, Kunio; Kuramoto, Akira*; Nozawa, Yasuko*; Toyama, Takeshi*; Nagai, Yasuyoshi*
no journal, ,
In order to characterize an inhomogeneity of heat affected zone (HAZ) in reactor pressure vessel (RPV) steels, effects of weld heat input and neutron irradiation have been investigated by SEM/EDX, 3D atom probe and positron annihilation methods. Coarse grain HAZ with/without post weld heat treatment (PWHT) showed higher toughness compared to base metal (BM) caused by mixed structures of lower-Bainite and Martensite. Fine grain HAZ before PWHT showed much higher strength and lower toughness due to Martensite-Austenite constituent (MA). After PWHT, FGHAZ toughness became similar to BM since MA disappeared. There are no clear differences among microstructures such as carbide, grain boundary for unirradiated HAZ materials and base metal, and Cu precipitation and irradiation damage for irradiated materials. Although HAZ materials of RPV steels might show equal or lower toughness compared to BM, irradiation embrittlement of HAZ materials would not become much larger than that of BM.
