Equilibrium Constants and Nitrogen Activity in Liquid Metals and Iron Alloys

Abstract

In the initial period of steel production with nitrogen as an alloy addition, from among the three thermodynamic factors, i.e. chemical composition, temperature and pressure, use was made of the first and the second factor only. Consideration given to the third factor created conditions for the realization of the “old” idea of steel ennoblement using nitrogen. An experimental setup for the investigation of the equilibrium state of chemical reactions in the gaseous phase–liquid metal system in the pressure range from 0.001 to 3.2 MPa and at temperatures not exceeding 2423 K has been constructed and is presented in this paper. This setup relies on the levitation metal melting technique, whereby the ceramic crucible is eliminated and does not take part in the reaction phenomena. Intensive induction mixing of the liquid metal and the rapid cooling of samples in the experiment period provide the reproducibility of a given state through chemical analysis of the frozen samples of metal. The solubility of nitrogen in liquid iron, chromium, nickel, cobalt, vanadium and iron alloys in the pressure range 0.001 to 3.2 MPa at various temperatures, was determined. The determined characteristics made it possible to develop a thermodynamic model describing the solubility of nitrogen, temperature and chemical composition in a wide range of variation of these factors. The established nitrogen–nitrogen interaction reduces the effectiveness of nitrogen introduced to the liquid steel.