Nearly 1.9 billion tons of steel are produced every year, making it the most important alloy in terms of volume and impact. While steel is a sustainability enabler, through lightweight design, wind farms and magnets, its primary production is the opposite. Iron is today reduced from oxidic iron ores using fossil carbon carriers. This produces >2t CO₂/t of steel, standing for >30% of the global greenhouse gas emissions in manufacturing. These emissions can be massively reduced when replacing carbon by hydrogen and hydrogen-containing mixtures as reductants [1,2].

The lecture presents recent progress in understanding the nucleation, transport and redox mechanisms of the phase transformations occurring during hydrogen-based direct reduction of iron oxides at the atomic scale. The kinetics of the reactions strongly depend on mass transport kinetics, nucleation during the multiple phase transformations, the oxide’s chemistry and microstructure, and on damage and fracture associated with the phase transformation and mass transport phenomena occurring during reduction. Understanding these effects is key to make hydrogen-based reduction of iron ores commercially viable, enabling massive CO₂ reductions in the metallurgical sector.

[1] Raabe D, Tasan CC, Olivetti EA. Strategies for improving the sustainability of structural metals. Nature. 2019 Nov; 575 (7781): 64-74. https://www.nature.com/articles/s41586-019-1702-5

[2] SH Kim, X Zhang, Y Ma, IR Souza Filho, K Schweinar, et al. Influence of microstructure and atomic-scale chemistry on the direct reduction of iron ore with hydrogen at 700° C, Acta Materialia, 2021. https://www.sciencedirect.com/science/article/pii/S135964542100313X