Reduced-Activation　Ferrite/Martensitie　(RAFM)　CLF-1　steel　thick　plates　currently　exhibit　extensive　applications　in　helium　cooled　ceramic　breeder　Test　Blanket　Module　(TBM)　building.　This　study　conducted　electron　beam　welding　(EBW)　of　T-joints　without　base　plates,　and　achieved　the　single-pass　welding　and　double-sided　forming　welding　of　CLF-1　thick　steel　plates　via　the　optimization　of　technological　parameters.　Moreover,　the　microstructure　and　mechanical　properties　of　two　welded　joints　were　systematically　investigated.　The　welds　in　both　joints　were　well-formed　with　no　defects,　such　as　pores,　incomplete　fusion,　and　cracks.　The　weld　zone　(WZ)　was　mainly　composed　of　tempered　martensite　laths.　No　obvious　δ-ferrites　appeared　in　the　weld,　and　numerous　MX　carbides　were　dispersed　in　the　martensite　laths.　The　coarse-grain　heat-affected　zone　(CG-HAZ)　near　the　fusion　zone　mainly　included　slender　batten-shaped　martensites　and　a　few　carbides.　The　fine-grain　heat-affected　zone　(FG-HAZ)　near　the　base　metal　(BM)　mainly　consisted　of　dual-phase　mixed　structures　of　tempered　sorbite　and　martensite.　The　tensile　strengths　of　the　two　welded　joints　at　room　temperature　were　621　MPa　and　623　MPa,　while　at　550,　they　were　350　MPa　and　363　MPa,　respectively.　The　fracture　positions　of　both　joints　were　located　in　the　BM.　The　microhardness　of　the　WZ　slightly　exceeded　that　of　the　BM,　while　HAZ　exhibited　no　apparent　softening.　The　mean　impact　absorbed　energy　values　of　the　welds　in　two　joints　were　296　J　and　297　J,　being　much　higher　than　that　of　the　BM.　Accordingly,　the　welded　joints　fully　satisfied　the　service　requirements.　©　2020　Elsevier　B.V.