日本金属学会誌

J. Japan Inst. Metals, Vol. 31, No. 7 (1967),
pp. 887-892

Effects of Carbon and Hydrogen on the Activity of Nitrogen in Austenite

Toshisada Mori1, Eiji Ichise1, Yasuo Niwa3 and Masaaki Kuga2

1Department of Metallurgy, Faculty of Engineering, Kyoto University, Kyoto
2Postgraduate Student, Kyoto University, Kyoto
3Postgraduate Student, Kyoto University, Kyoto; and now, Nippon Kokan Kabushiki Kaisya

Abstract:

The effects of carbon and hydrogen on the solubility of nitrogen in austenite have been measured by the use of the quenching method. To determine the effect of hydrogen, the pure iron specimens were equilibrated with N2+H2 gas mixtures, and the effect of hydrogen partial pressure on the solubility of nitrogen was investigated instead of determining the dissolved hydrogen contents because of the difficulty for analysing the dissolved hydrogen. The determination of the effect of carbon was performed under the atmosphere having a constant carbon potential in order to prevent the decarburization of specimens. The constant carbon potential atmosphere was prepared by adding CO+CO2 gas mixtures, having a fixed gas ratio, to the N2 gas flow. The results obtained are as follows:
(1) Hydrogen accelerates the denitrogenization when the cooling rate of the nitrogenized specimen is small, but
(2) Hydrogen has no effect on the activity coefficient of nitrogen in austenite, i.e.,

eN(H) = 0    (1050° ∼ 1250°C).

(3) The effect of carbon on the activity coefficient of nitrogen in austenite is expressed as
eN(C) = 395/T-0.183    (1050° ∼ 1250°C).

(4) The value of interaction parameter of carbon in austenite is smaller than that in liquid iron, which may be explained by the fact that upon fusion of iron, there is a drastic increase of lattice imperfections, i.e., holes which are capable of accomodating interstitial atoms.


(Received 1967/2/25)

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