# Technological Processes for Steel Applications in Nuclear Fusion
## 10 Summary and Conclusions  
### Fusion Welds  
Charpy tests on beam welded specimens (especially EB welds) have shown surprisingly good results, even without post-veld heat treatment. Just by tempering at 700 \({}^{\circ}\)C for 2 h, the Ductile-to-Brittle-Transition-Temperatures (DBTT) of Laser and EB welds were almost as good as those of the EUROFER97 base material with a shift of only 10-30 K. Difficulties of these weld processes are connected to the selection of the beam characteristic to adjust penetration depth and shape of the fusion zone, the formation of pores, and the surface preparation. The ductility of the 12 mm TIG weld was acceptable after a one-step PWHT of 740 \({}^{\circ}\)C for 2 h. The 5- and 10-mm TIG welds required a two-step PWHT. Also, the results might be interpreted to that effect that thinner plates are better suited for beam welding compared to thicker ones, while for TIG welds it seems to be the other way around. However, the most important result of these investigations is that EUROFER may be welded by TIG, EB or Laser techniques with the necessity of just a one-step post-welding heat treatment that may be performed below 750 \({}^{\circ}\)C, i.e., without preceding austenitization. However, beam welding should be preferred when PWHT is restricted to one-step tempering. Besides the encouraging Charpy test results of the welded plates we have also to mention the downsides: They lose creep-strength of about 40 MPa at 600 \({}^{\circ}\)C, but since the maximum operation temperature for EUROFER is 550 \({}^{\circ}\)C, the reduction in creep strength, which is about 20 MPa at 550 \({}^{\circ}\)C, might still be tolerable. Investigations have shown that this loss in creep strength results from fine grain formation in the vicinity of the HAZs. (Note: These creep studies are published in [38]).  
Finally, we present a list of conclusions and recommendations for further investigations on EUROFER welds:  
* Beam welds need fine adjustment to the specific geometry, especially power and feeding speed have to be adjusted for a correct penetration depth.  
* Misalignment after TIG welding is larger for thinner plates and has to be determined for a correct compensation (strongly depending on geometry).
* All observed weld defects did not lead to fracture initiation.
* Chemical composition of EUROFER filler wire is stable (no decarbonization).
* Negligible traces of delta-ferrite have been detected in 5 mm TIG welds.
* Extended softened zones form in TIG welds.
* Coarse grain formation occurs in TIG welds and in thick beam welds.
* Microstructure can only be restored by austenitization, i.e., annealing at temperatures above 900 \({}^{\circ}\)C.
* Only 5 mm EB welds might be acceptable regarding ductility without PWHT.
* Ductility of beam welds might be acceptable with just an one-step PWHT of T? 700 \({}^{\circ}\)C for 2 h (without austenitization).
* TIG welds seem to require austenitization (due to coarse grain as well as softening in the HAZ) or at least higher tempering temperatures (T? 740 \({}^{\circ}\)C).
* One-step PWHTs at temperatures less than 700 \({}^{\circ}\)C are not expedient.
* Tensile properties (transverse tests) are nearly independent of the weld type since fracture occurs in the base material.
* Future tensile studies should be performed just on untreated welds (in addition to creep and Charpy tests), since the results are not very informative.