Improvement of corrosion resistance, toughness and weldability of SUS329J4L for large thick plate applied for canister of spent fuel storage

SUS329J4L equivalent to ASTM A240 S31260 is selected for the candidate material of canister for the dry interim storage of spent fuels, for that shows excellent hot workability to manufacture into wide and thick plate and good corrosion resistance for canister usage at the present time. In order to improve the corrosion resistance, toughness and electron beam weldability which is applicable in future, candidate steel is investigated to obtain the suitable chemical compositions within the specification requirements, and the following results are obtained. (1) Some experimental alloys were melted in the laboratory to obtain the best balance of N and Ni contents for suitable toughness and corrosion resistance, as the contents of Cr and Mo contributed for corrosion resistance are maintained at upper limit of the specification requirements. The best balance is obtained more than 0.2 mass% in N and more than 6.5 mass% in Ni within the specification requirements. (2) The practical hot rolled plate melted with suitably selected compositions at 3 m in wide and 20 mm in thickness was manufactured with no defects in spite of higher nitrogen contents. The improved plate has satisfactory strength, high toughness and excellent corrosion resistance equivalent to austenitic super stainless steels.