Electron-beam (EB) welding is an important joining technique for fabricating and assembling blanket and first-wall components in fusion reactors. A numerical modeling of the EB procedure of a selected part of a DEMO fusion reactor blanket is presented. Stress and temperature distributions during and after EB welding are analyzed with the help of nonlinear finite element calculations, including phase transformations of MANET stainless steel. Residual stresses are discussed. Their magnitude and distribution may stimulate the initiation and growth of surface cracks parallel to the weld. Analysis of postweld heat treatment shows that the residual stresses can be neglected if appropriate postweld heat treatment is performed. The main drawback of this analysis seems to be the lack of appropriate material data for high temperatures close to the melting point. Despite this, qualitative statements on the feasibility of joints are possible, and improved analyses of welding stresses are expected to make a valuable contribution to future studies that address the safety and reliability of blanket structures.