Corrosion behaviors of inconel 617 in hydrogen base gas mixture
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INTRODUCTION
HIGH temperature gas-cooled reactors (HTGR) appear to be promising sources of energy for process heat. In Japan, the direct steel making system that utilizes heat from H T G R has been developed for the last ten years? Asphalt will be reacted endothermically with high temperature helium gas from H T G R with the result that a hydrogen base gas mixture will be produced. The refined hydrogen base gas mixture will be then heated up to about 850 ~ by the helium outlet gas from H T G R at the heat exchanger and will be used to reduce iron o r e s . 1,2 For such plants, the materials for the heat exchanger will have to withstand long time exposure to high temperature corrosive gas atmospheres. The materials will be attacked by oxidizing and/or carburizing (decarburizing) gases. This attack can pose serious limitations to the life of the heat exchanger in the direct steel making system. Corrosion behaviors of materials in impure helium atmospheres have been studied in several nations where HTGRs have been developed, and many excellent articles have been published over the last twenty years. 3-9 On the other hand, relatively few papers have appeared about high temperature properties of materials in hydrogen base gas mixtures, although some coalgasification systems have been developed in a few countries. 10-~2 National Research Institute for Metals (NRIM) in Japan has been conducting research and tests of high TATSUO SHIKAMA, TATSUHIKO TANABE, MASAKAZU FUJITSUKA, MASAHIRO KITAJIMA, HEITARO YOSHIDA, and RYOJI WATANABE are with the Nuclear Materials Division, National Research Institute for Metals, (Tsukuba Branch), 1-2-1 Sengen, Sakura-Mura, Niihari-Gun, Ibaraki-Ken, 300-31, Japan. Manuscript submitted September 18, 1979.
temperature properties of several nickel base heat resistant superalloys in some impure helium environments, which simulate primary coolants for a H T G R reactor core, and in a hydrogen base gas mixture simulating the reducing gas for iron ores in the direct steel making system. In the present paper, corrosive behavior of Inconel 617 in the high temperature hydrogen base gas mixture will be described. Our results have shown that alloying elements, A1, Ti, and Cr in Inconel 617 were oxidized. A protective Cr203 film containing titanium oxide was formed at elevated temperatures. The aluminum was internally oxidized at 900 and 1000 ~ The Inconel 617 was partially carburized at 650 and 900 ~ Carbides of Mo, Ti, and of Si were formed a few hundred/zm beneath the surfaces exposed for up to 200 h at 900 ~ II. E X P E R I M E N T A L PROCEDURES Inconel 617, the nickel base heat resistant superalloy, whose chemical composition is shown in Table I, was exposed to the hydrogen base gas mixture of 80 pct H 2 + 15 pct CO + 5 pct CO/(hereafter denoted as the test reducing gas) at 900 ~ for up to 1500 h and at 650 and 1000 ~ for 200 h. The chemical composition of the test reducing gas is tabulated in Table II. The gas pressure was 9.8 • 104 Pa and gas flow rate was 300 ml/min in testing. The specimen confi
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