Effect of Oxygen Content Upon the Microstructural and Mechanical Properties of Type 316L Austenitic Stainless Steel Manu
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isostatic pressing (HIP) is the process by which metal components are fabricated from the consolidation of a metal powder of required chemistry, to bulk material via the application of high temperature and isostatically controlled pressure, under an inert atmosphere.[1–3] HIP permits several advantages over conventional forging and casting procedures, the most significant being the possibility for near-net shape manufacture.[2–6] Because consolidation occurs in a prefabricated vessel, the vessel may be developed to allow HIP of a component with a relatively complex shape and geometry, of which might only be possible via forging through machining or additional welded joints. This advantage can result in significantly reduced associated machining and welding costs, less wasted material due to fewer machining stages, increased design ADAM J. COOPER, Postdoctoral Research Associate, is with the School of Materials, University of Manchester, Oxford Road, M13 9PL, U.K. Contact e-mail: [email protected] NORMAN I. COOPER, Head of Materials Technology, is with BAE Systems, Bridge Road, Barrow-in-Furness, LA14 1AF, U.K. JEAN DHERS, Manager of Areva Research and Development, is with AREVA, Lyon, France. ANDREW H. SHERRY, Chief Scientist, is with the National Nuclear Laboratory, Birchwood Park, Warrington, WA3 6AE, U.K. Manuscript submitted November 26, 2015. Article published online June 22, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
freedom, as well as easier inspection via nondestructive examination techniques due to HIP’s tendency to produce components with much smaller grain sizes than chemically equivalent forged materials. Furthermore, Hot Isostatically Pressed (HIP’d) materials typically display increased yield strengths, UTS, and enhanced ductility over ‘‘chemically equivalent’’ forged counterparts, which is generally attributed to HIP’s smaller grain size and isotropic grain structure, exhibiting no grain directionality like that of rolled plates. However, although HIP is a relatively popular manufacture route toward components employed in oil and gas, as well as the aerospace industry, the more extreme safety concerns associated with the nuclear sector require much greater insight into the potential issues regarding HIP, and as such, HIP is yet to launch as a serious rival to forging and casting for the manufacture of components used within integral parts of a nuclear reactor, specifically those which are subjected to irradiation damage. Before it is introduced, components fabricated by HIP must stand up to all of the basic standards and code cases set by conventional forged components, in order to justify implementation of a different manufacture route. One particular issue surrounding HIP manufacture of austenitic stainless steel concerns the concentrations of oxygen that remain in the austenite matrix after HIP and ultimately have a detrimental effect upon the material’s Charpy impact toughness.[7–9] Although this is a VOLUME 47A, SEPTEMBER 2016—4467
well-known metallurgical phenomenon which is not r
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