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Authors: Dong Su Bae, Sang Ll Lee, Seung Hoon Nahm, J.W. Choi, H. Takahashi
Abstract: The high Mn-Cr austenitic steel for structure material of nuclear and/or fusion reactors from the point of view of the reduced radio-activation has been irradiated by using three irradiation modes of electron-beam irradiation, electron-beam irradiation after He-injection and electron/He+-ion dual-beam irradiation in 1250kV high voltage electron microscope (HVEM) connected with an ion accelerators to study the effect of He-injection on irradiation damage. Irradiation-induced segregation analyses were carried out by an energy dispersive X-ray analyzer (EDX) in a 200kV FE-TEM with beam diameter of about 0.5nm. Void formation was not observed in each irradiation condition. Grain boundary migration was observed in the case of electron/He+-ion dual-beam irradiation. Irradiation-induced segregations of Cr and Mn at grain boundary were observed in each irradiation condition. The amounts of Cr and Mn segregation decreased in the cases of electron-beam irradiation after He-injection compared with other irradiation conditions.
Authors: Dae Whan Kim, Chang Hee Han, Woo Seog Ryu
Abstract: Fatigue tests of type 316 and 316LN stainless steel were conducted at RT and 600ı, 0.8~1.5% strain range for low cycle fatigue (LCF), 300~600ı, 0% strain range for thermal fatigue (TF) and 300~600ı, 2% strain range, in-phase or out-of-phase for thermomechanical fatigue (TMF). LCF, TF, and TMF lives were increased but saturation stresses were decreased with the addition of nitrogen. The higher temperature was the lower TF life at a same temperature change. The minimum temperature change for TF failure was more than 100ı. TMF life was higher at inphase condition than at out-of-phase condition. Fracture mode was transgranular for LCF and outof- phase of TMF and almost transgranular and small intergranular for TF and in-phase TMF.
Authors: Woo Gon Kim, Hyun Hie Kim, Kee Bong Yoon, Woo Seog Ryu
Abstract: This paper is to evaluate the creep crack growth rate (CCGR) of the type 316SS series: 316SS, 316FR and 316LN, and to apply a creep ductility model. A number of the data are collected through wide literature surveys and experiment, and evaluated by the C* parameter. The results of the CCGR data were nearly matched with a small scattering band regardless of the different applied stresses, temperatures and test specimens configuration. In the CCGR, type 316FR and 316LN steels were slower than type 316SS. Type 316SS showed a better agreement in the application of the creep ductility model than the type 316FR and 316LN steels.
Authors: V. Voyevodin, V. Bryk, O. Borodin, I.M. Neklyudov, N. Akasaka, S. Onose
Abstract: Results of analysis of swelling behaviour of alloying austenitic steels are described from the point of view of the cooperative interaction of defect structure, solid solution decay and precipitates evolution.
Authors: Qiu Xu, Toshimasa Yoshiie, Takuya Nagasaka, Takeo Muroga
Abstract: To investigate the effect of impurites, such as O, N and C, on migration behavior of vacancies in several types of V-4Cr-4Ti vanadium alloy with different amount of impurites from 207wppm to 866wppm were irradiated with 28 MeV electrons using an electron linear accelerator at 100 K. After irradiation, positron lifetime measurements were carried out. Single vacancies were produced in all samples. The vacancy clusters were formed at 348 K and 433 K in samples with lowest and highest impurites, respectively. The temperature forming vacancy clusters incresased with increaisng amount of impurites. The vacancy migaration is depended on the amount of impurities rather than the kind of impurity.
Authors: Zhenyu Yao, Akihiro Suzuki, Takuya Nagasaka, Takeo Muroga
Abstract: A V-4Cr-4Ti alloy and pure V were oxidized in flowing argon for 0.5-8h and subsequently annealed in vacuum for 16h at 973K. The oxygen of 1000-9000ppm was introduced into the V-alloys with little nitrogen, where oxygen was concentrated in region near the surface. By the annealing, oxygen was homogeneously diffused into depth of 150µm. The diffusion depth of oxygen in V-4Cr-4Ti is much smaller than that of pure V, because of Ti-O precipitates formed as oxygen trap. The study indicated that it is feasible to control oxygen level and distribute in the surface region of the vanadium alloys.
Authors: Takeo Muroga, Takuya Nagasaka, A. Nishimura, J.M. Chen
Abstract: Potential enhancement of mechanical properties of V-4Cr-4Ti by controlling precipitates of interstitial impurities (C, O and N) was investigated by means of various thermal and mechanical treatments. The increase in the cold working degree resulted in band structure of coarse Ti-CON precipitates having enhanced impact properties. Solid solution heat treatment followed by re-heating resulted in the formation of high density Ti-O-C precipitates enhancing high temperature strength. Combination of re-heating and cold rolling enhanced further the strength. Improvements in thermal and mechanical treatments are discussed for application of V-4Cr-4Ti to fusion structural materials.
Authors: Hisao Kinoshita, Benfu Hu, H. Takahashi
Abstract: The effects of helium and aging treatment on radiation damage behavior in low activation Fe-Cr-Mn ( W, V) alloy were investigated by electron and helium ion dual-beam irradiation in a high voltage electron microscope. Specimens were aged at 673 K, 823 K and 923 K for 1000, 3000 and 10000 hours. Electron and He ion dual-beam irradiations were performed at 627 K to 10 dpa. M23C6 type carbides were precipitated in the aged specimens, and the amount of the precipitates was increased with increasing aging temperature and aging time. He bubbles were formed during dual-beam irradiation in all of the specimens. The cavity swelling under dual-beam irradiations was increased with increasing the aging temperature and aging time. It was suggested that cavity swelling is closely related to the concentration of solutes such as Cr and C in the matrix, namely cavity growth rate becomes higher with decreasing of the solutes in solution.
Authors: Chong Hong Zhang, Yue Sheng Wang, K.Q. Chen, Ji Guo Sun, J.M. Quan, Chang Qi Chen
Abstract: Low-activation Fe-Cr-Mn alloy and 316L stainless steel were irradiated with 92 MeV Ar ions at about 500°C, to fluences of 0.8~1.7×1021 ions m-2 .After irradiation, cross-sectional specimens were investigated with transmission electron microscopy.Cavities with high number density were observed in the peak dose regions. The cavity number density reaches maximum at Ar concentration peak, while cavity mean size is consistent with displacement damage profile. It is indicated that Ar atoms can enhance cavity formation in a manner similar to helium. There are thresholds of dose and dose rate for the bi-modal size distribution of cavities. The significant growth of a small portion of cavities in the peak damage region at the highest ion-fluence is ascribed to the effect of interactive sink strength of cavities.
Authors: Benfu Hu, Hisao Kinoshita, Tamaki Shibayama, H. Takahashi
Abstract: The effect of helium on irradiation damage behavior in Fe-Cr-Mn(W,V) steel was investigated by electron/helium ion dual-beam irradiation. The results indicate that helium can promote the increase of dislocation density and enhance the void nucleation and void swelling of Fe-Cr-Mn(W、V) alloy. The segregation of solute elements near grain boundary was suppressed by existence of helium. Also the interface of carbide-matrix migration and the change of solute concentration near the interface were observed during dual-beam irradiation.

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