Improve inclusion control in recycled steel for net-zero manufacturing

Secondary steel manufacturing involves complex and energy-intensive processes that rely on precise control of alloy composition and microstructure manipulation, mainly in downstream stages. While the current approach has been successful, largely due to a good understanding of solid-state processing, it heavily depends on energy-intensive primary metal to maintain low concentrations of key elements known to be detrimental. If carbon neutrality is to be achieved by 2050, an urgent transition to more sustainable metals manufacturing and increased utilization of low-carbon, higher impurity recycled metal is needed. However, producing alloys from diverse scrap sources, whether increased or lower-grade, leads to the accumulation of tramp elements. Even trace amounts of elements like Cu, Sn, and Zn can segregate in semi-solid regions, resulting in grain boundary decohesion and the formation of damaging defects and secondary phases, including non-metallic inclusions (NMIs).

The project aims to investigate how elevated levels of Cu, Sn, and Zn impact the nucleation and growth of secondary inclusions and defects during the late stage of solidification when segregation is well-developed. Limited knowledge exists about this environment, and understanding the interdependency of fundamental phenomena is crucial for comprehending the dynamic evolution of microstructure during solidification and subsequent solid-state transformations.

The research will primarily employ in-situ approaches based on X-ray imaging to explore the dynamic formation of microstructure and study how to engineer the nucleation and growth of non-metallic inclusions throughout the entire thermomechanical history of the materials, from the liquid to the rolling step. Post-mortem characterization methods, including SEM and EBSD, will also be utilized to understand the crystallography and orientation relationships between various phases. This part of the project may also involve atomistic modelling to explore the elemental effects on inclusion formation and develop new inoculants and modifiers. The studentship is part of two extensive collaborative EPSRC projects involving the Materials and Engineering departments at Oxford, Loughborough University, and STFC. The project will also be linked to others ongoing collaborations in the field of sustainable metals, including academic collaborators at the Max-Planck Institute (Germany), Diamond Light Source and the European Synchrotron Research Facility (ESRF, France).