# Technological Processes for Steel Applications in Nuclear Fusion
## 2 Eurofer97  
Within the European Fusion research program, the first so-called low-activation alloys CeTa and TaHf were produced in 1986. For these, all alloying elements with long decay times due to high activation by neutron irradiation (Nb, Mo, Ni, Al) were substituted by Ta, W, and Ce. The alloys were specified along the lines of international fusion material development programs. A variety of CrWVTa experimental alloys (LA series) had been already produced and tested, in particular by the Culham Laboratory/British Steel, UK. The specification of the alloys was based on activation calculations which, at that time, were characterized by contradictions regarding element activation due to different spectra, computation methods, and nuclear data libraries. At that time, at least in part, only simple neutron-induced collision processes were taken into account. Nonetheless, the introduction of sequential reactions allowed to plot generally accepted decay curves, which formed the basis for a new set of specifications for low activation steels. In these, several alloying elements were rejected or limited (Hf, Ta, W) and new upper limits were obtained for all tramp elements that would increase the activation. Part of these limits is found to be in the ppm and sub-ppm range and cannot be fully achieved metallurgically and analytically. This is the reason why these steels are also referred to as reduced activation ferritic/martensite (RAFM) steels. Then, the development line of the OPTIFER (Optimized Ferrite) alloys started at Forschungszentrum Karlsruhe in 1992 within the framework of the European Long-term Programme. The OPTIFER alloys are 9.5% Cr-Mn-V-Ta steels with 1% W or variants with germanium replacing tungsten. Parallel to the work on OPTIFER, a Japanese version of an 8% Cr-Mn-V steel with 2% W has been investigated since 1994. This RAFM steel, called F82H-mod, was produced as a batch of 5 tons by JAERI/NKK and made available in form of plate materials by IEA to European laboratories for joint examinations. Based on the physical, mechanical, and structural data obtained for OPTIFER and F82H-mod, combined with the findings made by various European institutes with regard to low activation alloys (UK, France), BATMAN alloys (Italy), and OPTIMAX steels (Switzerland), a specification was set up for a European reference alloy--the EUROFER steel. Funded by the European Commission, the first so-called EUROFER97 batches were ordered from Bohler Edelstahl GmbH, Austria, in 1998. Motivation for this industrial heat can be summarized as follows:  
* Gathering experience with the industrial production of a high purity steel and comparison with experimental heat production details. * Gathering information about forming properties, homogeneity of mechanical and structural properties, and targeting specified mechanical and microstructural characteristics. * Gaining technological results from the production of a test blanket module with respect to forming and weldability. Five melts were produced by vacuum arc-melting in a rotating electrode facility (ROTEL) and casted into cylindrical blocks of about 2 tons each. Thereafter, the blocks were remolten in another vacuum arc melting (VAR) facility: 3 blocks with diameters of 510 mm, 2 blocks with diameters of 410 mm. The 3 bigger blocks were then forged into slabs with cross-sections of 190 mm \(\times\) 520 mm and the 2 smaller blocks were round forged to diameters of 200 mm. The slabs were hot-rolled to one plate of 8 mm, one of 14 mm, and two of 25 mm thickness at temperatures between 1150 \({}^{\circ}\)C and 1180 \({}^{\circ}\)C. The following final heat treatment was conducted: 980 \({}^{\circ}\)C for 27 min, followed by air cooling to room temperature, and tempering at 760 \({}^{\circ}\)C for 90 min, followed by air cooling. The final plate dimensions were 3500 mm \(\times\) 1500 mm \(\times\) 8 mm, 3600 mm \(\times\) 1500 mm \(\times\) 14 mm, and 3800 mm \(\times\) 1200 mm \(\times\) 25 mm. In addition, a 1.5 mm thick plate was produced.