Contribution of Sodium Metasilicate to the Diffusion of Mn in Steel under Tribological Contact at High Temperatures

The environmentally friendly sodium metasilicate is regarded as one of the promising lubricants for hot metal formation because of its excellent thermal stability and unique physical chemistry property. This work aims to reveal how alkaline silicate reacts with manganese (Mn) in mild steel during tribological contact at high temperatures. The results suggest that the melted sodium metasilicate contributes to the diffusion of Mn from mild steel because of the combined effects of the chemical potential gradient and the different oxidation states of Mn in the steel substrate and melts. The hierarchical structure of the tribo-interface indicates that a Mn-rich layer containing fingerlike and mushroomlike oxides, such as Mn2O3, NaMnO2, and MnFe2O4, exists between the iron oxide scale and the sodium-rich layer, which acts as a barrier to the inward diffusion of oxygen.