Spatially-resolved investigation of oxide scale formation in hydrogen and natural gas combustion atmosphere for spring steel on a semi-industrial scale

This study investigates the effect of different combustion atmospheres — natural gas/air versus hydrogen/air — on phase formation in oxide scales on a spring steel. Spring steel samples were oxidized at 1100 °C for 90 min in a semi-industrial scale furnace. The scale was analyzed layer-by-layer using X-ray diffraction and additional characterization using synchrotron radiation. No significant differences in phase composition were observed between the two atmospheres. Scanning electron microscopy and energy-dispersive X-ray spectroscopy provided detailed insights into chemical gradients, particularly at the metal–scale interface. Silicon diffusion along primary grain boundaries was identified as a key factor promoting serration formation, which enhances scale adhesion. The chemical behavior and phase distribution within the scale remained consistent across both atmospheres, confirming that hydrogen combustion does not adversely affect scale composition. However, the consistency of chemical characteristics is a crucial aspect of material behavior and effective scale removal. This supports the viability of hydrogen as a sustainable alternative fuel used in steel production. • Comparison of natural gas and hydrogen as fuel for heat treatment furnaces. • Oxidation in a semi-industrial scale furnace. • Layer-by-layer examination for spatial resolution of oxide scales. • Formation of silicon-rich phases along primary gain boundaries. • Synchrotron examination of the cross-section.