Effects of chemical composition and dose on microstructure evolution and hardening of neutron-irradiated reactor pressure vessel steels

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

https://doi.org/10.1016/j.jnucmat.2010.04.008

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.

Analyses of core Shroud materials by three dimensional atom probe (Contract research)

Kondo, Keietsu; Nemoto, Yoshiyuki; Miwa, Yukio; Kaji, Yoshiyuki; Tsukada, Takashi; Nagai, Yasuyoshi*; Hasegawa, Masayuki*; Okubo, Tadakatsu*; Hono, Kazuhiro*

JAEA-Research 2006-013, 39 Pages, 2006/12

JAEA-Research-2006-013.pdf:4.57MB

There has been an increasing number of stress corrosion cracking (SCC) incidents on low carbon austenitic stainless steels used in boiling water reactor (BWR) environments. To reveal the acceleration factor of intergranular crack propagation from the viewpoint of solute distribution in stainless steels, the material extracted from a core shroud of Japanese BWR was analyzed by the three dimensional atom probe (3DAP), which has the highest spatial resolution among the various microanalytical techniques. It was revealed by statistical analysis on 3DAP data that solute elements, such as Fe, Cr, Ni, Mo, Mn, Si, are randomly distributed in matrix of the shroud material. This result means that solute was not segregated or precipitated and was not form spinodal decomposition during the service. The concentration profile in the vicinity of grain boundary obtained from 3DAP dataset showed the random distribution of Cr. This result shows that degradation of the corrosion resistance induced by depletion of Cr was not responsible for the crack propagation along grain boundaries in low carbon stainless steel. On the other hand, enrichment of Mo and Si was observed at grain boundary. The width of the enriched zone was about 2 nm across the grain boundary, and the concentration of those elements could be much higher than the concentration obtained by field emission transmission electron microscopy/energy dispersive X-ray spectroscopy (FE-TEM/EDS). Therefore, it is necessary to study about the effects of enrichment of Mo and Si as a potential contributor to SCC.

Studies of formation structures of ultrafine Cu precipitates in Fe-Cu model alloys for reactor pressure vessel steels using positron quantum dot confinement in the precipitates by their positron affinity, JAERI's nuclear research promotion program, H13-034 (Contract research)

Hasegawa, Masayuki*; Nagai, Yasuyoshi*; Tang, Z.*; Yubuta, Kunio*; Suzuki, Masahide

JAERI-Tech 2003-015, 137 Pages, 2003/03

JAERI-Tech-2003-015.pdf:9.03MB

no abstracts in English

Effects of neutron-irradiation induced intergranular phosphorus segregation and hardening on embrittlement in reactor pressure vessel steels

Nishiyama, Yutaka; Onizawa, Kunio; Suzuki, Masahide; Nagai, Yasuyoshi*; Toyama, Takeshi*; Hasegawa, Masayuki*; Kameda, Jun*

no journal, , 

The effects of intergranular P segregation and hardening on the ductile-to-brittle transition temperature (DBTT) in several neutron-irradiated reactor pressure vessel steels with different bulk contents of P and Cu have been investigated using a scanning Auger microbe, a local electrode atom probe and positron annihilation spectroscopy. Increasing the neutron fluence at 563 K promotes intergranular P segregation. The content of P significantly affects irradiation hardening due to distinct formation of P-rich precipitates arising from the stabilization of vacancies. Analyzing the correlations between the P segregation, hardening, fraction of intergranular fracture and DBTT, it is found neutron irradiation mitigates an embrittling effect of segregated P, and therefore the hardening more strongly affects the DBTT shift than the P segregation.

Atom probe analysis of an aged overlay clad on reactor pressure vessel

Takeuchi, Tomoaki; Nishiyama, Yutaka; Onizawa, Kunio; Kameda, Jun*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Hasegawa, Masayuki*

no journal, , 

Microstructure evolution and hardening were investigated on stainless overlay clads of RPV aged at 400C for 10,000 h using three-dimensional local electrode atom probe (3DAP) and microhardness. In ferrite phases, a 12% of Cr concentration fluctuation observed before the aging was progressed to 25% after the aging while the wave length of the fluctuation was almost not changed about 8-10 nm before and after the aging. These feature indicated the fluctuation was arisen through a spinodal decomposition, which probably caused the age-hardening.