Reducing carbon dioxide emissions from steelmaking requires more efficient ways to turn iron ore into iron. While hydrogen-based technologies offer a promising path toward lower-carbon steel production, conventional blast furnaces will remain important during the transition. Understanding how iron ore behaves inside these furnaces could help improve their efficiency and stability.

A research team led by Associate Professor Shungo Natsui at Tohoku University, in collaboration with Tata Steel Europe, Delft University of Technology, and the National Institute of Advanced Industrial Science and Technology (AIST), has developed a new method to predict the mechanical properties of iron ore pellets under extreme heat. By combining high-energy X-ray computed tomography (CT) with chemical analysis and computer simulations, the team can estimate how strongly iron-rich structures resist deformation as temperatures rise.

Inside a blast furnace, iron ore pellets undergo a series of changes as they are heated and chemically reduced. They gradually soften and eventually melt. Under the weight of the surrounding materials, the pellets deform, narrowing the spaces between them through which gases flow. This can restrict gas movement and affect furnace performance. However, conventional experiments have largely relied on measurements of overall bed shrinkage and gas pressure loss, making it difficult to determine how changes within individual pellets contribute to the behavior of the entire packed bed.

To investigate these processes, the researchers conducted high-temperature experiments that reproduced conditions inside a blast furnace. Using high-energy X-ray CT, they reconstructed the internal structures of the pellets in three dimensions at different temperatures. At 1,300°C, a relatively rigid shell of metallic iron helped the pellets withstand the applied load. At 1,400°C, components that form slag became concentrated inside the pellets as softening progressed. By 1,550°C, the pellets had melted sufficiently for liquid material to drip away.

The team then used a particle-based simulation method called Moving Particle Hydrodynamics-Implicit (MPH-I) to reproduce the observed deformation. By comparing the simulated results with the three-dimensional CT images, they estimated how the effective yield stress of the iron-rich shell changes with temperature. Yield stress describes how much stress a material can withstand before it begins to deform permanently. Measuring this property directly under blast furnace conditions is challenging.

The key advance is a way to estimate the mechanical properties of iron ore pellets from their observed three-dimensional deformation, rather than relying solely on measurements of the overall packed bed. Linking X-ray imaging with numerical simulation provides a new approach to understanding how individual pellets respond to heat and pressure, and how their behavior affects gas permeability throughout a furnace.

The findings could help researchers better predict the deformation of iron ore beds and assess how different raw materials perform under high-temperature conditions. The team plans to extend the approach to other types of iron ore and hydrogen-rich reducing environments. In the longer term, this technology could support the selection of suitable raw materials and the development of more stable, efficient operating conditions as the steel industry moves toward lower-carbon production.