A review of the corrosion and wear resistance mechanisms of gas nitriding on steel

This article presents a systematic evaluation of the mechanisms, recent process advances, and practical applications of gas nitriding for improving the corrosion and wear resistance of steels. It first revisits the thermodynamic and kinetic foundations of conventional gas nitriding, with particular emphasis on ammonia dissociation, nitrogen potential regulation, and the coupled processes of surface adsorption, dissolution, and diffusion. Subsequently, the microstructural characteristics of the compound layer and diffusion layer are summarized, and their respective roles in controlling frictional behavior and electrochemical performance are discussed. Emerging catalytic nitriding techniques, such as surface nanocrystallization (e.g., UNSM, SMAT, and SP), pre-oxidation-assisted gas nitriding, rare-earth or alloy-element catalysis, laser-assisted gas nitriding, and low-temperature nitriding, are reviewed. A comparative analysis highlights their effectiveness in improving hardness, wear resistance, and corrosion resistance. In addition, the synergistic mechanisms by which nitrided layers suppress micro-electrochemical heterogeneity, facilitate the formation of dense passivation films, and improve resistance to abrasive and adhesive wear through the dispersion of fine nitrides are analyzed. Finally, key scientific and engineering challenges are identified, particularly the absence of quantitative models describing corrosion-wear coupling at the microscale. In response to these gaps, prospective research directions are proposed, including multiscale mechanistic studies, high-fidelity simulations, scalable industrial routes for efficient low-temperature nitriding, and data-driven process-structure-property prediction frameworks enabled by machine learning. Collectively, this work establishes a theoretical foundation and research roadmap for optimizing nitriding processes and accelerating their industrial application in high-reliability engineering components.