Double-sided friction stir welding of Nitronic-40 stainless steel for application in tokamak devices

摘要

Nitrogen containing austenitic stainless steels(N-ASS)are widely utilized to fabricate various structural components in tokamak type fusion reactors owing to their suitable mechanical and functional proper-ties.These components are exposed to a range of temperatures(4-500 K)and interact closely with the magnetic fields that are used to control and contain the plasma within the tokamak systems.Nitronic-40(N40)or XM-11 stainless steel is one such N-ASS used for fabricating structural components in the mag-netic and vacuum vessel systems in tokamak devices.Fabrication of most of the larger components in the magnetic and vacuum vessel systems typically involves some type of fusion-based welding process.This study presents a double-sided friction stir welding(FSW)approach as an alternative to fusion welding processes to join 12 mm thick N40 plates to obtain joints with a low fraction ofδferrite(a detrimen-tal ferromagnetic phase),high joint efficiency,no sensitization and loss of hardness in the heat affected zone,and minimal nitrogen desorption from the weld nugget.The double-sided FSW approach yielded superior weldments when compared to similar joints accomplished by fusion welding for application in tokamak devices.