Calculation of changes in specific volumes of Fe – C system alloys depending on carbon content and temperatures

The work presents a new technique for determining the temperature dependence of the alloy specific volumes in Fe – C equilibrium system based on known from the literature calculated and empirical dependence for account of the phases’ specific volumes. These data were based on the independent reports of S.F. Yuryev and were obtained for temperatures below 1200 °C. When using these forms at temperatures above 1200 °C, the specific volume of austenite exceeds specific volume of ferrite. However, it is known that austenite has the smallest specific volume among all phases of the Fe – C system. In this regard, in the field of high temperatures, it is proposed to use other dependences that do not contradict the physics of polymorphic and phase transformations in this system. Thus the authors have obtained the general expressions for calculating the alloys’ specific volumes separately for three intervals of carbon concentrations in which the change in shares of the temperature phases are calculated according to Fe – C equilibrium diagram using the lever relation. As an example, results of the calculated determination of specific volumes of alloys with carbon vontent of 0.05, 0.13 and 0.33 % in the temperature range of 20 – 1600 °C are considered. The presented results are compared with the results obtained with the help of the phase diagram calculation package JMatPro®, on the basis of which the adequacy of the proposed calculation method was established. The developed technique can be used to calculate not only specific volumes of alloys, but also their density and coefficient of linear expansion depending on temperature and carbon concentration. It is the basis for the correct use of methods for determining the size of continuous cast billets due to shrinkage in order to correctly configure the equipment of continuous casting machines.

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