Investigation of Reaction Mechanisms During Vacuum Processing of Low-Carbon Steels

Abstract

The article investigates the thermodynamic activation barriers and pressure-driven reaction pathways governing gas–metal interactions during industrial vacuum treatment of low-carbon steels. Vacuum treatment remains one of the most effective secondary-metallurgy techniques for improving steel cleanliness by removing dissolved gases and stabilizing melt chemistry. However, despite extensive research on hydrogen and nitrogen degassing, limited attention has been given to the thermodynamic activation barriers and pressure-driven reaction pathways that control gas–metal interactions under industrial vacuum conditions. A new theoretical framework supported by industrial-scale experimental data obtained at “Baku Steel Company” is proposed to clarify the role of pressure, activation energy, and equilibrium transformations during vacuum refining of low-carbon steels. The proposed model integrates Gibbs free-energy landscapes, activation-energy analysis, and pressure-dependent pathway reconstruction to explain how gas desorption transitions from a reaction-controlled regime to a diffusion-dominated process as vacuum levels decrease. Using experimentally derived kinetic coefficients and pressure profiles, activation-energy values for hydrogen and nitrogen desorption were estimated, revealing a nonlinear decrease in energy barriers as the vacuum level approached the sub-mbar range. The analysis further shows that pressure-induced shifts in equilibrium significantly modify the reaction coordinate, altering both the depth and the slope of the free-energy well. The results demonstrate that industrial vacuum refining is primarily governed by thermodynamic driving forces, providing a unified thermodynamic–kinetic basis for process optimization.