The Materials Science Behind Sustainable Steel ProductionAbstractIron- and steelmaking stand for about 8% of all global greenhouse gas emissions, which qualifies this sector as the biggest single cause of global warming [1,2]. This originates from the use of fossil carbon carriers as precursors for the reduction of iron oxides. Carbon is turned in blast furnaces into CO and – through the redox processes reducing iron oxide – into CO2, producing about 2 tons CO2 for each ton of steel produced.Mitigation strategies pursue the replacement of fossil carbon carriers by sustainably produced hydrogen and / or electrons as alternative reductants, to massively cut these CO2 emissions, thereby lying the foundations for transforming a 3000 years old industry within a few years [1,2].As the sustainable production of hydrogen using renewable energy is a bottleneck in green steel making, at least during the next decade (transforming this industry would need about 300 Million tons of green hydrogen each year, i.e. about 5 orders of magnitude more than produced around the globe today), the gigantic annual steel production of 1.85 billion tons requires strategies to use hydrogen and / or electrons very efficiently and to yield high metallization at fast reduction kinetic.This presentation presents progress in understanding the governing mechanisms of hydrogen-based direct reduction and plasma reduction of iron oxides and also shows how these methods work for other transition metal reduction processes [2-5]. The metallization degree, reduction kinetics and their dependence on the underlying redox reactions in hydrogen-containing direct and plasma reduction strongly depend on mass transport kinetics, Kirkendall effects, nucleation phenomena during the multiple phase transformations, chemical and stress partitioning, the oxide's chemistry and microstructure, the acquired (from sintering) and evolving (from oxygen loss) porosity, crystal plasticity, damage and fracture effects associated with the phase transformation phenomena occurring during reduction [5-8]. Understanding these effects, together with external boundary conditions such as other reductant gas mixtures (including also ammonia [8]), oxide feedstock composition [9], pressure and temperature, is key to produce hydrogen-based green steel and design corresponding direct reduction shaft or fluidized bed reactors (with and without plasma support), enabling the required massive C02 reductions at affordable costs. Possible simulation approaches that are capable of capturing some of these phenomena and their interplay are also discussed [3-8].BiographyDr. Dierk RaabeProf. Dr. habil. Dr. h.c.Managing Director, Max Planck Institute for Sustainable MaterialsMax-Planck-Str. 1, 40237 Duesseldorf, GermanyEmail: d.raabe@mpi-susmat.dehttps://www.mpi-susmat.dehttps://www.mpie.de/2763408/microstructure_physics_and_alloy_designDierk Raabe studied music, metallurgy and metal physics (summa cum laude) at RWTH Aachen (Germany). After his doctorate 1992 (summa cum laude) and habilitation 1997 at RWTH Aachen he received a Heisenberg fellowship and worked at Carnegie Mellon University and at the High Magnetic Field Lab in Tallahassee. He joined Max Planck Society as a director in Düsseldorf at the Max Planck Institute for Iron Research (now: Max Planck Institute for Sustainable Materials) in 1999. His main research interest is Sustainable Metallurgy, i.e. to make industrial production, use and recycling of materials more sustainable, focusing on basic research with high leverage for CO2 emission mitigation and lower energy consumption. His specific interests are in sustainable metals (specifically ���green’ steel, Nickel, Aluminium, Titanium etc.), recycling-oriented material design, metal physics, interfaces, phase transformation, atom probe tomography, materials theory, hydrogen, and artificial intelligence methods in materials science. He received the Gottfried Wilhelm Leibniz Award (Highest German Science Awards) and two ERC Advanced Grants (Highest European Research Grant). He is professor at RWTH Aachen (Germany) and at KU Leuven (Belgium). He is a Doctor Honoris Causa at the Norwegian Technical University Trondheim. He is a member and Senator of the German National Science Academy Leopoldina and of the US National Academy of Engineering. ZOOM MEETING LINK: https://wpi.zoom.us/j/93538117042