03pC03
低放射化フェライト鋼の高速引張変形挙動
High-speed tensile deformation of reduced-activation ferritic steel
石井 大貴1，笠田 竜太2，小西 哲之2，大畑 充3，安堂 正巳4，谷川 博康4
D. Ishii1, R. Kasada2, S. Konishi2, M. Ohata3, M. Ando4, H. Tanigawa41

京大エネ科（院生）, 2京大エネ理工研, 3阪大工, 4原子力機構
1,2
Kyoto U., 3Osaka U., 4JAEA

1. Introduction
In fusion reactor, huge electromagnetic forces areloaded on the structural materials by eddy currents
induced by the plasma disruption within 10ms].
Obviously, the possible strain rate of structuralmaterials during plasma disruption events is a
design-dependent and operation-dependent parameter.
Tanigawa et al. have calculated eddy current
distribution generated by the disruption. Plasma
current of 16.7MA was assumed to linearly decreasein 30 ms [1]. Substantial electromagnetic forces areloaded on the blanket structures across the large
toroidal magnetic field. In this case, estimated strain
rate during current plasma disruption event is 0.1/s.
According to the safety management of fission reactor
pressure vessel steels, dynamic fracture toughness willbe the key property to guarantee the structural safetyof nuclear power plants including fusion reactor.
However there is no sufficient data of dynamic tensile
properties and dynamic fracture toughness of
reduced-activation ferritic (RAF) steel F82H.
Generally, the tensile strength and toughness of bcc
alloys have temperature dependence. Considering thethermal activation process of gliding dislocation
responsible to the deformation, therefore, highstrain-rate may have an impact on the mechanicalproperties of RAF steels. In addition, irradiation
damage may have a significant impact on thestrain-rate sensitivity. Objective of this study is toinvestigate the high-speed tensile deformation
behavior of RAF steel F82H.
2. Experimental procedure
The material used in this study is F82H BA-07
heat. The specimens used are small round bar type of
which gauge length and diameter is 10 mm and 2 mm.
High-speed tensile tests were carried out using
Hydroshot HITS-T10, SHIMADZU Co. Testing
temperatures were 296 K and 423 K. Nominal strainrates were from 0.01 from 1400 s-1. Fracture surface
was observed by scanning electron microscopy (SEM)
using JEOL JSM-5600LV.
3. Results and discussion

Nominal stress-strain curves obtained by thehigh-speed tensile machine were shown in Fig. 1 (a) at276 K and (b) at 423 K. The results clearly show
strain-rate effect on the both of strength andelongation at 296 and 423K. Both nominal stress andnominal fracture strain increased with strain-rate.
However the reduction of area obtained by SEM
resulted in the similar values as shown in Fig. 2.
Modified R parameter with considering temperaturerising during the high strain-rate deformation canexplain the temperature dependence of the tensile
strength with different strain-rates. The higher strengthwith higher strain-rate can be explained by activation
volume analysis, suggesting a change of deformation
mechanism from kink-pair formation to dislocationinteraction. The mechanism of higher uniform
elongation with higher strain rate will be discussed
through a true stress-strain approach.

Fig.1 S-S curves of F82H obtained from high-speed
tensile tests.
Fig.2 Reduction ofarea (ROA) of
F82H after testing.

[1] H. Tanigawa et al., 24th IAEA Fusion EnergyConference – IAEA CN-197, Oct. 2012, USA.