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Abstract: The oxide dispersion strengthened (ODS) steels are being developed and investigated for fission and fusion structural applications in Japan, Europe, and the United States. In this paper, the fracture toughness and tensile properties of an ODS steel with nominal composition Fe–12Cr–2.5W–0.4Ti–0.25Y2O3 (designated 12YWT) were investigated and compared to commercial reduced-activation ferritic/martensitic (RAFM) steels. Small, 1.6-mm thick and 3.2-mm wide, 3-point bend specimens were used for fracture toughness characterization of this steel. Specimens were fatigue pre-cracked to initial crack length (a) to width (W) ratio of 0.45 and tested quasi-statically in the temperature range from −50°C to 550°C. Specimens tested up to 50°C exhibited elastic–plastic cleavage fracture that was typical for the transition region in ferritic steels. The master curve transition temperature, T 0, for the 12YWT alloy was determined to be 102°C. Specimens tested at 100°C and higher exhibited ductile stable crack growth. In these cases, the J-integral at the onset of stable crack growth (J Ic) was determined from the J–R curves. Their equivalent values in terms of stress intensity factor, , were about 93MPa√m at 100°C and decreased to 53MPa√m at 550°C. This study showed that oxide dispersion strengthening resulted in significant decreases in the toughness properties compared to commercial RAFM steels, although appreciable level of toughness was still retained. Tensile tests were performed at temperatures between room temperature and 800°C. As expected, this material exhibited very high yield strength, ∼1300MPa, at room temperature. For comparison, the yield strength of commercial RAFM steels is about 550MPa. Yield strength of 12YWT decreases as test temperature increases and at 800°C it is about 323MPa. [Copyright &y& Elsevier]

Abstract: The status and key issues of reduced activation ferritic/martensitic (RAFM) steels R&D are reviewed as the primary candidate structural material for fusion energy demonstration reactor blankets. This includes manufacturing technology, the as-fabricated and irradiates material database and joining technologies. The review indicated that the manufacturing technology, joining technology and database accumulation including irradiation data are ready for initial design activity, and also identifies various issues that remain to be solved for engineering design activity and qualification of the material for international fusion material irradiation facility (IFMIF) irradiation experiments that will validate the data base. [Copyright &y& Elsevier]

Abstract: Irradiation hardening and fracture toughness of reduced-activation ferritic/martensitic steel F82H after irradiation were investigated with a focus on changing the fracture toughness transition temperature as a result of several heat treatments. The specimens were standard F82H-IEA (IEA), F82H-IEA with several heat treatments (Mod1 series) and a heat of F82H (Mod3) containing 0.1% tantalum. The specimens were irradiated up to 20dpa at 300°C in the High Flux Isotope Reactor under a collaborative research program between JAEA/US-DOE. The results of hardness tests showed that irradiation hardening of IEA was comparable with that of Mod3. However, the fracture toughness-transition temperature of Mod3 was lower than that of IEA. The transition temperature of Mod1 was also lower than that of the IEA heat. These results suggest that optimization of specifications on the heat treatment condition and modification of the minor alloying elements seem to be effective to reduce the fracture toughness-transition temperature after irradiation. [Copyright &y& Elsevier]

Abstract: This work investigates irradiation response in the joints of F82H employed for a fusion breeding blanket. The joints, which were prepared using welding and diffusion welding, were irradiated up to 6dpa in the High Flux Isotope Reactor at the Oak Ridge National Laboratory. Post-irradiation tests revealed hardening in weldment (WM) and base metal (BM) greater than 300MPa. However, the heat affected zones (HAZ) exhibit about half that of WM and BM. Therefore, neutron irradiation decreased the strength of the HAZ, leaving it in danger of local deformation in this region. Further the hardening in WM made with an electron beam was larger than that in WM made with tungsten inert gas welding. However the mechanical properties of the diffusion-welded joint were very similar to those of BM even after the irradiation. [Copyright &y& Elsevier]

Abstract: Several types of reduced activation ferritic/martensitic (RAFM) steel have been developed over the past 30years in China, Europe, India, Japan, Russia and the USA for application in ITER test blanket modules (TBMs) and future fusion DEMO and power reactors. The progress has been particularly important during the past few years with evaluation of mechanical properties of these steels before and after irradiation and in contact with different cooling media. This paper presents recent RAFM steel results obtained in ITER partner countries in relation to different TBM and DEMO options. [Copyright &y& Elsevier]