Reduced activation ferritic/martensitic (RAFM) steels are considered the main candidate material for the water-cooled ceramic breeder (WCCB) in a fusion reactor. High-energy density welding approaches, such as electron beam welding (EBW) and laser beam welding (LBW), are frequently utilized in the welding of RAFM steels. During the welding process, cracks and other defects are prone to appear. In this paper, EBW was selected for the welding of RAFM steels. Those with and without pre-heat and post-heat treatment by electron beams are studied by finite element simulation and trials. The results show that the experimental results are consistent with the simulation. In particular, in the case of similar deformation, the residual stress after electron beam heat treatment is far less than that without heat treatment. Without heat treatment, the residual stress near the weld is more than 400 MPa, while the residual stress after heat treatment is about 350 MPa. As the reduction of residual stress is essential to prevent the occurrence of cracks and other defects after welding, pre-heat and post-heat treatment by the electron beam is deemed as an effective way to greatly improve the welding quality in RAFM steel welding.

Vacuum electron beam welding (EBW) is selected as the welding of the water-cooled ceramic breeder (WCCB) blanket. In the process of welding the first wall (FW) of WCCB blanket, it is necessary to add a backing plate to the arc section. At this stage, the thickness of reduced activation ferrite/martensite (RAFM) steels is up to 31 mm. In this article, thick plate RAFM steels after hot isostatic pressing (HIP) are welded by EBW, and then different heat treatments are performed. The results showed that, in the welding condition, hardness of welded joints was changed slightly. The highest hardness of the joint is 440 HV while the lowest is 290 HV, and a softening zone was observed in the heat-affected zone (HAZ). Moreover, after different heat treatments, the welding seam changed into the tempered martensite. In addition, the hardness of base metal and welded joints is all reduced, and the performance of welded joints in quenched and tempered conditions is better than that in normalized and tempered conditions.

The structural material of the water-cooled ceramic breeder (WCCB) blanket is reduced activated ferrite/martensite (RAFM) steels. The first wall (FW) of one of its components is realized by hot isostatic pressure (HIP) diffusion welding and vacuum electron beam welding (EBW). In order to study the performance difference of electron beam welded joint of RAFM steels before and after heat treatment, the EBW test of RAFM steels was carried out, and the welded joint was quenched and tempered treatment. The properties of welded joints before and after quenched and tempered treatment were studied. The results show that the microstructure of the weld is composed of $\delta $ ferrite and coarse lath martensite. After quenching and tempering treatment, the microstructure of the joint changes into tempered martensite with no obvious martensite characteristics. Moreover, $\delta $ ferrite disappears, and carbide precipitates out at the original austenite grain boundaries. Here, the type of precipitated carbide is M ₂₃ C ₆ as characterized by the electron backscatter diffraction analysis.