Effects of O, Se, and Te on the rate of nitrogen dissolution in molten iron
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I.
INTRODUCTION
I T is important to know the rate of nitrogen dissolution into molten iron and its alloys for the efficient control of the nitrogen content of steel. For this reason, various kinetic studies have been conducted by many investigators; we also investigated the rate of nitrogen dissolution into pure ironm and the effects of additional Ti, Zr, V, and Cr, which have stronger affinities for nitrogen than Fe, I21 on the reaction rate using an isotope exchange reaction. From these results, the enhancement of the reaction rate by such elements as Ti, Zr, V, and Cr was observed and correlations with thermodynamic affinities were found. On the other hand, it is well known that the reaction rate of nitrogen with liquid iron is depressed by surface active solutes, such as oxygen and sulfur, and their effects are explained by applying some site-blockage models by such elements at the metal surface. I3-8] However, it is difficult to know their effects accurately and some discrepancies between many investigators can be found regarding the effect of oxygen at lower concentration in particular. Although it is considered that selenium and tellurium affect the reaction rate considerably because they are more surface active than oxygen or sulfur, only a few measurements have been made to prove this.I9,~01 In the present work, the effects of oxygen, selenium, and tellurium on the rate of nitrogen dissolution in molten iron have been investigated by an isotope-exchange reaction at 1973 K, and their effects are discussed with regard to the rate-determining step. Moreover, the adsorption coefficient of each element derived from the present results is compared with that from surface tension.
HIDEKI ONO, Graduate Student and Research Fellow of Japan Society for the Promotion of Science, KAZUKI MORITA, Associate Professor, and NOBUO SANO, Professor, are with Department of Metallurgy, The University. of Tokyo, Bunkyo-ku Tokyo, It3, Japan. HIROKAZU FUKAGAWA, formerly undergraduate student, Department of Metallurgy, The University of Tokyo, is Engineer, with Hitachi Powder Metals Co. Ltd., Minoridai, Matsudo, Chiba, 271, Japan. Manuscript submitted May 30, 1995. 848--.VOLUME 27B, OCTOBER 1996
II.
EXPERIMENTAL
Experimental details have been described elsewhereY ,21 The subjects related to the present study are discussed in the following sections.
A. Measurement of the Effect of O.rygen An alumina crucible containing high-purity electrolytic iron with 2 ppm S weighing 30 g was inserted into a transparent quartz furnace tube and inductively heated in an argon and hydrogen gas mixture. When the temperature of molten iron reached 1973 K, the flow rates of argon and hydrogen were fixed and the gas mixture was introduced into a water vapor saturator (0 to 80 mass pct H2SO4 at 303 to 343 K) to control water vapor pressure and maintain the desired oxygen activity in the sample. After holding 1 to 2 hours, argon in the flowing gas mixture was replaced by nitrogen, which contains about 1 at. pct nitrogen isotope, 3~ 2, and measuremen
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