Development of welding technique between PNC-FMS wrapper tube and SUS316 steel. 3. Evaluation on strength properties of weld zone

It is necessary to carry out welding of Ferritic/Martensitic steel (PNC-FMS) wrapper tube with the austenitic stainless steel (SUS316, entrance nozzle, handling head) in order to apply to the real wrapper tube of Experimental Fast Reactor 'JOYO' and Proto type FBR 'Monju'. If the δ ferrite phase is formed at heat affected zone in welded PNC-FMS, toughness degradation would be suspected. For preventing the δ ferrite formation, PNC-FMS/SUS316 complex wrapper tube, which were welded by TIG at round tube condition before cold drawing, were developed. In this study, the mechanical properties of PNC-FMS/SUS316 complex wrapper tube were evaluated to make the material design base standard of PNC-FMS. The results obtained are summarized as follows. (1) In tensile test, fracture occurred at location of base metal, not PNC-FMS welded interface. Thus, tensile strength of welded PNC-FMS/SUS316 is equivalent to base metal or more. (2) Impact property of the welded part is superior to base metal. Its fracture toughness, bendability are equivalent to base metal. The creep rupture and fatigue properties of the welded part are slightly inferior to base metal, but both values are still beyond design base standard of base metal. (3) The tensile and impact properties of the welded part are degraded by thermal annealing, but the amount of their degradation is the same as that of base metal. (author)