Development of XM-19 fasteners for the IWS blocks assemblies

Fasteners of XM-19 material were developed for the first time in INDIA for the IWS block assemblies for the ITER Vacuum Vessel. Total quantity of fasteners required for the IWS block assembly is around 97000. Fasteners are manufactured from chromium-manganese-nickel austenitic stainless steel type XM-19,UNS S20910 bars in accordance with A479/A479M-04 Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels (identical to SA-479/SA-479M ASME Edition 2007). The high strength, corrosion resistance, and low magnetic permeability of this alloy allow it to be used for IWS block assembly. XM-19 possesses strength and corrosion resistance that is higher than stainless steel grades 316, 316/316L, 317, and 317/317L. Development of fasteners for the first time with XM-19 material itself is associated with challenges to acquire the required mechanical properties after heat treatment. Other activities which are important for the manufacturing of fasteners are tolerance to be kept while hot forging, development of die for hot forging, shrinkage allowance, thread rolling, slotting on the threads, and selection of heat treatment method to retain the mechanical properties. The various stages of manufacturing of M30 bolts, M30 nuts and M20 cap crews from raw material to the finished product, challenges faced during manufacturing and how it were resolved will be explained in this paper