Mechanical properties of full austenitic welding joint at cryogenic temperature for the ITER toroidal field coil structure

•No significant distribution of tensile strengths at 4K, 77K and room temperature along welding thickness of 200mm manufactured by one side narrow gap TIG welding with FMYJJ1.•Tensile strengths at cryogenic temperature of welded joint are increased with increasing of C+N contents of base material.•In the case that welded joint is manufactured by combination of different base materials, strength at 4K of welded joints are below strength of base material having higher C+N contents. ITER toroidal field coil (TFC) structures are large welding structures composed of coil case and support structures made of heavy thick high strength and high toughness stainless steels. Japan Atomic Energy Agency plans to apply narrow gap Tungsten Inert Gas (TIG) welding with FMYJJ1 (0.03C–10Mn–12Cr–14Ni–5Mo–0.13N) which is full austenitic stainless filler material. In order to evaluate effect of base material thickness and combinations of base material on tensile properties, tensile tests were performed at room temperature, 77K and 4K by using tensile specimens taken from 200mm thickness welded joints of two combinations of base materials and 40mm thickness welded joints of four combinations of base materials. As the results, it was confirmed that there were no large distribution of yield and tensile strength along the thickness of welded joints of 200mm thickness and yield and tensile strengths of welded joints were decreased with decreasing of C+N contents of base material.