Ferroalloys and Stainless Steels with Low Carbon Footprint via Hydrogen Reduction of Oxide Blends

Northwestern University, Evanston IL

Investigators

Abstract

This award supports fundamental research related to advanced steelmaking, enabling a drastic reduction of carbon dioxide (CO2) emissions responsible for global warming and its impact on the US land and population. Using green hydrogen, instead of coke (a form of carbon), iron and other ores are directly transformed, in a single step, to alloy steels, such as stainless steel (containing iron, nickel and chromium) which is used extensively in consumer and high-tech applications. The hydrogen is obtained by splitting water with renewable electricity. This research investigates the thermodynamics and kinetics of hydrogen reduction of blends of iron and other metal oxides using in situ x-ray diffraction and theoretical modeling. This project supports the development of a domestic hydrogen economy and contributes to industrial decarbonization. It improves modernization and competitiveness of the US steel industry, thus benefiting the US economy and society. The process leverages various disciplines including manufacturing, metallurgy, and x-ray diffraction science leading to new educational opportunities. The project broadens participation of women and underrepresented groups in research and trains the next generation of engineers needed to boost domestic production of high-value alloyed steels. Hydrogen reduction of Fe2O3 is a complex process due to the presence of transient phases, FeO and Fe3O4, and large volume changes during reduction. Hydrogen reduction of oxide blends to create, in a single step, ferroalloys and alloy steels, introduces additional complexity, as the interactions between oxides of iron and the other elements, such as nickel, chromium, tungsten, molybdenum and manganese, lead to acceleration of reduction kinetics, shift in thermodynamic stability, and formation of further transient phases. This research studies the mechanisms underlying these effects and the microstructures and properties of the final alloys, seeking a deeper understanding of direct hydrogen reduction as it applies to various alloyed steels and ferroalloys. This project studies how one-step, one-pot hydrogen reduction of oxide blends to create alloy steels and ferroalloys greatly improves the reduction kinetics while also being more efficient than a multiple step process where individual alloying elements are created and then combined with iron to make alloy steels. The project develops a fundamental understanding of co-reduction of oxide mixtures of iron and alloying elements to achieve metallic binary and ternary ferroalloys useful for production of various steels. Hydrogen reduction of oxide blends is studied via in-situ x-ray diffraction to assess the reaction kinetics and phase formation and CALPHAD, phase-field, and finite-element modeling to improve the understanding of and provide predictions of reaction mechanisms. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.