Contributions from research on irradiated ferritic/martensitic steels to materials science and engineering
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INTRODUCTION
OVER the last 15 years, there has evolved a major change in the specification of steels for irradiation environments. Prior to 1974, the undisputed materials choice for liquid metal-cooled reactor (LMR) structural components was AISI 316, an austenitic stainless steel in the 17 pct Cr range with 13 pct Ni and 2 pct Mo (all compositions given as weight percent). The choice was based on good high-temperature properties, excellent corrosion resistance, and ease of fabrication and welding. That choice was fn'st challenged following the observation that AISI 316 developed cavities during neutron irradiation, indicating a volumetric expansion of the material now called "swelling. "tl] Swelling, and its associated phenomenon ~irradiation creep," proved to be the life-limiting factors in the application of AISI 316 for LMR fuel cladding. The discovery that cold working to the level of about 20 pct delayed the development of swelling t2] allowed interim use of AISI 316. In about 1974, a concerted effort was begun to find a replacement alloy, in order to permit optimization of fast breeder reactor systems. t3] That program, initially called the Alloy Development Program and later changed to the National Cladding/Duct Materials Development Program, was similar to British, French, Japanese, and Russian efforts. The program was initially funded by the Atomic Energy Commission (AEC), later by the Energy Research and Development Administration (ERDA), and finally by the Department of Energy (DOE). The Alloy Development Program took as its mission the testing of altemate alloys for fast breeder reactor structural applications. The major goal was to reduce the tendency for irradiation-induced swelling, but at the same time, other materials properties such as creep, rupture D.S. GELLES, Staff Scientist, is with Battelle Pacific Northwest Laboratory, Richland, WA 99352. This paper is based on a presentation made in the symposium "Irradiation-Enhanced Materials Science and Engineering" presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25-29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD. METALLURGICAL TRANSACTIONS A
strength, and postirradiation tensile strength were measured. A wide range of alloys was investigated, including austenitic, ferritic, and martensitic steels, nickel-base superalloys, and molybdenum- and niobium-base alloys. The primary candidates were titanium-stabilized austenitic steels and precipitation-strengthened superalloys. Martensitic steels were included initially as a low-priority option based on observations of swelling inhibition in the ferrite phase of a ferritic/austenitic dualphase steel, t41 and that martensitic steel would retain this swelling inhibition but maintain good high-temperature properties. However, as it became apparent that titanium stabilization only delayed the onset of swelling tS'6,Tj and precipitation strengthening led to severe postirradiation emb
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