Seiichi Kaga

Effects of neutron irradiation on strength of fusion reactor materials and their electron beam welded joints

Abstract Several aluminum alloys (A7N01, A5083 and A6061) and a ferritic martensitic steel (JFMS) were used in the present study of the effects of neutron irradiation on the strength of base materials and their electron beam welded joints. Neutron irradiation tests were performed using the core irradiation facility at Kyoto University Reactor (KUR). Neutron fluences were 2.0 × 1022 9.1 × 1022 and 1.7 × 1023n/m2 (E > 0.1 MeV). Tensile tests were performed at 4.2, 77 and 293 K on miniature specimens prepared from both the base and welded materials. Aluminum alloys exhibit serrations in the nominal stress-nominal strain curve at 4.2 K. Little effect of neutron irradiation on the serration is observed. The ductility decrease of base metal and welded joints of aluminum alloys by neutron irradiation is smaller than that of JFMS. JFMS, especially welded joints, showed strong radiation embrittlement at cryogenic temperatures.

Study on Optimization of Welding Condition and Joint Efficiency in Friction Welding(1st Report). Optimazation of Friction Welding Condition for S45C Carbon Steel.

The combination of welding condition (optimum welding condition) which produced maximum tensile strength of S45C carbon steel friction welded joint under the notched tensile test specimen condition was investigated using response surface method.As a result, the combination of welding condition to yield maximum tensile strength at the weld was attained through a steepest ascent path. And, a second-order equation predicting the weld strength was accurately established.By the result of confirmation experiments using the predicting equation, a successful weld was obtained under the optimum welding condition. But, the optimum welding condition requires comparatively larger burn off quantity. Therefore, it is needed to consider a economical view such as less burn off quantity. Moreover, the observation of the successful welds showed that a fine grain ferrite perlite layer having comparatively low hardness widely distributed over the heat affected zone of the weld.

Effect of neutron irradiation on the strength of electron beam welded JFMS steel

Abstract Japanese ferritic-martensitic steel (JFMS) is a candidate material for nuclear fusion reactor application. It is material for high temperature use. Structural materials of the fusion reactor will be exposed to neutron irradiation. In order to research the fundamental properties of the material under irradiation, low temperature strength of JFMS steel and its electron beam welded joints were investigated under various irradiated conditions in this experiments. It was shown that strength decreases at low temperature in the base metal and, in electron beam welded joints of JFMS steel, increases with increasing neutron fluence.

A STUDY ON STRESS CORROSION CRACKING OF AN EXPLOSIVELY PLUGGED PART

ABSTRACT Studies on the stress corrosion cracking of an explosively plugged part were conducted. SUS 304 stainless steel was used as testing material. The distribution of residual stress in plug and tube plate after plugging was obtained. The effect of residual stress on the stress corrosion cracking was studied. Residual stress in tube plate near the plug was compressive and stress corrosion cracking did not occur in the tube plate there. However it occurred on the inner surface of plug because of residual tensile stress in axial direction of the plug. Stress corrosion tests in MgCl 2 solution under constant load were conducted. The susceptibility to stress corrosion cracking of the explosive bonded boundary was lower than that of base metal. Stress corrosion tests in high temperature and high pressure pure water were also conducted by means of static type of autoclave but stress corrosion cracking did not occur under the testing condition used.