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., e_N^(H) = 0 (1050° ∼1250°C).
(3) The effect of carbon on the activity coefficient of nitrogen in austenite is expressed as e_N^(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.
