Welding state of art for Eurofer 97 application to Tritium Blanket Module for ITER Reactor

Full text of publication follows: Eurofer weldability must be established for data base assessment and TBM manufacturing support. Electron Beam, Hybrid (Laser combined with MIG/MAG), Laser and Narrow Gap TIG processes have been carried out on Eurofer samples from 0.5 mm to 40 mm. Electron Beam produces very narrow fusion zone width, in the range of 3 to 4 mm, that yields brittle joints with (5-ferrite. This process is considered only for low penetration depth (cooling plates). The other processes produce similar results, with attenuation or enhanced effects, depending on cooling rates and weld penetration depth. Pre- and post-heating have been applied on hybrid and laser welds. High hardness values, increasing brittleness and softening effects in the Heat Affected Zone are observed for each welding configuration that could signal creep problems. The Fusion Zones are typically composed of martensite laths, with small grain sizes. In the Heat Affected Zones, martensite grains are observed with M23C6 carbide precipitation. Delta ferrite has been observed only in Electron Beam welds, due to very high cooling rate during the solidification phase, related to strong enhanced weld shape. Eurofer filler wire with optimized chemical composition is developed for producing welds with good properties. To restore properties after welding, PWHT seems is necessary and several treatments including one at 750 deg. C for 2 hours have been performed. Also tries is a re-austenisation treatment of 10 h at 1050 deg. C. affecting order to improve results, pre- and post-heating has been applied. The heating produced by the resistive heater was too low, and new welding tests are planned at higher temperatures (400 deg. C). However, the pre- and post-heating at higher temperatures will complicate manufacturing of TBM clamping For penetration depths below 10 mm, laser process is the reference method and TIG second. Distortion level performed by laser process is acceptable for manufacturing stage. For TIG and laser processes, no metallurgical defect or damage has been observed. HAZ and Fusion Zones are larger in TIG welds compared with laser welds. Six TIG welding passes are necessary, compared to the two passes for laser process. For laser and Hybrid (MIG/Laser) welding process, joint coefficient can be considered as 1. All tensile specimens have broken outside the welds, and in the parent base material. For laser welds, tempering Post Welding Heat Treatment has markedly reduced the hardening level in fusion zone, to acceptable values in the range of 300 HV 10. Impact tests have shown good results. Welding simulation has been carried out, and numerical martensitic weld width is close to real one. (authors)