A. Balandin, S. Saiyara, G. Kennedy, R. Speyer, N. Thadhani, J. Kacher
Georgia Institute of Technology,
United States
Keywords: hydrogen reduction, extrusion-based fabrication, net-shaped steel, process intensification
Summary:
Hydrogen reduction of metal oxides offers a promising pathway toward sustainable steel production, However, the high cost of hydrogen reduction relative to blast furnace technology limits the feasibility of this method. In this work, we investigate a process-intensified approach that integrates extrusion-based net-shape fabrication with hydrogen reduction to produce net-shaped stainless and maraging steel parts directly from oxide precursors. High-purity metal oxides are mixed and formulated into extrudable pastes, and shaped into net-shaped green bodies through an extrusion process. Extrudable pastes are formulated by shear mixing high-purity metal oxides, Methylcellulose binder, and surfactants. These mixtures are extruded through a piston-driven system using net-shaped dies. The resulting green bodies are dried, reduced, and sintered under controlled hydrogen flow, converting them into dense, alloyed metallic components. By tailoring the solids loading and oxide composition, efficient extrudability is achieved, ensuring uniform extrusion and reknitting in the net-shaped components. Composition tuning further enables the production of a range of steel alloys suited to different applications. By tuning die design based on application, a variety of parts with geometric complexity can be produced. Green bodies are characterized using X-ray fluorescence to verify uniform metal oxide powder distribution. Metal components are characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to confirm complete reduction and compositional uniformity, ensuring that the final metal part is comparable to its conventional alloyed counterpart. Components are further characterized using mechanical testing to confirm that they have similar strength to conventionally manufactured steels. Optimized net-shaped stainless steel parts with a honeycomb geometry achieved approximately 20% of the bulk density while maintaining nearly 80% of the axial strength of fully dense counterparts. This integrated approach unites shape-forming and metallurgy into a single process, providing a new framework for the process in which a metal component with an advanced geometry is achieved, using steel produced from domestic sources. Taconite tailings, found around mining sites in the US can be recovered, magnetically separated, ground, and flocculated or bioleached to yield high-purity iron oxide powders, which would be directly used in hydrogen-reduced extruded parts. Future efforts will focus on extending this method to alternative alloy systems, such as Ni-based and refractory alloys, exploring diverse geometries for lightweight, net-shaped metallic structures suited for heat exchangers and other functional components, and evaluating scalability through continuous extrusion.