Tensile and impact properties changes of HASTELLOY X after exposure in high-temperature helium environment
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I.
INTRODUCTION
H A S T E L L O Y X and HASTELLOY XR are being considered as one of the major high-temperature alloys for structural component applications in high-temperature gascooled reactors (HTGR) in JAERI (Japan Atomic Energy Research Institute). Materials selection for many of plant components of HTGR is strongly influenced by the high temperature and long life (20 years) required by the reactor design. Thus, it is necessary to develop a high degree of understanding concerning the long-time thermal response of alloy structures and subsequent effects on mechanical properties. The potential interaction of structural metals with primary coolant (helium) impurities is of first concem in reactor design, since it is known that the microstructures and mechanical properties of high-temperature alloys can change during long-time exposureJ l'zl Therefore, extensive experimental programs are currently in progress at JAERI to examine the HTGR helium corrosion behavior and its influence on the mechanical properties of HASTELLOY X and HASTELLOY X R . I3'4] This paper summarizes the results of the structural and mechanical properties changes of HASTELLOY X after use in the liner tube of the HENDEL hot gas duct exposed in high-temperature helium gas for about 6000 hours. The changes in microstructures, roomtemperature impact toughness, and room and elevatedtemperature tensile properties on HASTELLOY X were examined.
II.
E X P E R I M E N T A L PROCEDURES
A. Operating History of HENDEL Hot Gas Duct The HENDEL hot gas duct consists of three layers of ceramic fiber insulation (AI20 3 and SiO2), pressure tube *HASTELLOY is a trademark of Cabot Corporation. YASUO KONDO and KAZUHIKO KUNITOMI, Research Engineers, KIYOSHI FUKAYA, Chief, and YOSHIAKI M1YAMOTO, Head and Principal Engineer, are with the Department of High Temperature Engineering, Tokai Research Establishment, Japan Atomic Energy Research Institute, Tokai-Mura, Naka-Gun, Ibaraki-Ken, 319-11, Japan. Manuscript submitted May 5, 1987. METALLURGICALTRANSACTIONS A
(SB42, JIS), and the liner tube (HASTELLOY X). (See Figure 1.) The hot gas duct has been operated 13 cycles since February, 1982. The total operating time was about 6000 hours, and accumulated operating time at helium gas temperature of above 800 ~ was about 1000 hours. Table I shows the total operating time at each helium gas temperature. The CO/CO2 ratio of the helium was in the range of 1/ 1 to 1/ 10, in 13 cycle operations. The thermodynamically estimated surface oxidation reaction in this condition is selective oxidation of relatively active elements (Mn, Si, AI, Ti, and Cr), while the major constituent nickel is inert. But, there is the possibility of oxidation of iron which is another major constituent, t51 B. Materials and Test Procedures The liner tube was made from rolled and solution-annealed sheets of commercial HASTELLOY X of 6 mm thickness. Specimens were taken from the two kinds of liner tubes. One is used in the HENDEL hot gas duct in high-temperature helium gas, and the other is an unexposed (
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