It is necessary to control and calculate the nitrogen content in the metal during the production of nitrogen-containing steel in order to determine in advance the conditions for obtaining a given grade of steel. For this, a thermodynamic calculation should be used, which describes the solubility based on the parameters of the interaction of nitrogen with alloying elements in iron.

There are different approximations of the calculation, which include the interaction parameters of the first, second, second and first order and their various combinations and temperature dependences. A comparison was made of various methods of calculating the solubility of nitrogen in 10Cr14NMn15 steel, in particular, the Wagner method, the Chipman and Corrigan method, the calculations of V.I. Lakomskyi with co-authors, analytical and experimental material by J. Pitkälä with co-authors and others.

Chromium-manganese steels have high plasticity in a wide range of temperatures and can be used in cryogenic technology. Manganese is an austenizer of steel, it stabilizes the austenite structure at room and lower temperatures. Manganese is cheaper than nickel, but is a less effective austenizer. Therefore, these elements can often be used together.

Nitrogen, as a substitute for nickel, is a much stronger austenizer. A small amount of nitrogen in steel releases a large amount of nickel. Thus, a nitrogen content of 0.1% in chrome-nickel steels is equivalent to 1.5%–2.5 % Ni [1].

Now a large number of studies on the microstructure, properties, mechanisms of deformation, strengthening and destruction of austenitic chromium-manganese steels, including those doped with nitrogen, have appeared [2–8]. Therefore, the purpose of the study was to compare the thermodynamic calculation of nitrogen solubility in 10Cr14NMn15 steel by different authors and the experimentally determined solubility.

The calculation using the Wagner interaction parameters of the first and second order gave the following result for the temperature 1873 К:

Using only the first-order interaction parameters in the calculation, as done by Wagner, gave a larger and, in our opinion, less likely estimate of nitrogen solubility.

The calculation according to the Chipman–Corrigan equation [9], which allows taking into account the influence of temperature on interaction parameters, made it possible to obtain the following data for a temperature of 1873 K:

The advantage of using the Chipman-Corrigan equation remains the ability to calculate solubility at any temperature, but with approximately the same temperature effect on all interaction parameters.

Taking into account the temperature dependence of the interaction parameters when calculating the solubility according to the works of V.I. Lakomskyi and V.V. Lakomskyi was reflected in their monograph [10]. In the case of steel 10Cr14NMn15, the calculation gave the following results:

The formula given in [11] was obtained using averaged literature data and the authors' own experimental data. That is, the authors obtained an averaged dependence that made it possible to obtain for the temperature 1873 К:

To determine the differences in the solubility values obtained by different authors, a calculation was made for the temperature range 1873–2300 K, the results of which are shown in the fig. 1.

Fig. 1. The effect of temperature on the estimated solubility of nitrogen in 10Cr14NMn15 steel: 1 – Wagner's method taking into account the effect of temperature; 2 – the Chipman-Corrigan method; 3 – calculation according to the formulas of V.I. Lakomskyi [10],                  4 – calculation according to the formula of Pitkälä J. with co-authors [11]

Experimental determination of the solubility of nitrogen at a temperature of 1923 K showed that the Sieverts constant is 0.306775, and the obtained dependence has the following form:

Thus, it is quite justifiable to estimate the solubility of nitrogen in 10Cr14NMn15 steel according to the formulas of V.I. Lakomskyi. The calculation error in this case is on the level 5 %.

It is sufficient to maintain the partial pressure of nitrogen in the system at the level of 0.3–0.7 atm to obtain 10Cr14NMn15 steel with a nitrogen content of 0.15–0.25 % when the melt is saturated from the gas phase at a temperature of 1923 K.

References:

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