Sustainable Fe–Cr–Ni Stainless Steels via Hydrogen Reduction of Blended Oxides

Hydrogen reduction of iron oxide is a promising solid-state, moderate-temperature steelmaking approach with no direct CO2 emission. However, alloy steels require alloying elements such as Cr, whose oxides are too thermodynamically stable to be reduced by hydrogen when they are in pure form. Blends of Fe2O3, NiO, and Cr2O3 particles are shown here, using in situ X-ray diffraction and ex situ metallography, to undergo a sequential hydrogen reduction up to 1300 °C, for two Fe–Cr–Ni alloys with low-Ni (Fe-18Cr-8Ni, wt %) and high Ni (Fe-18Cr-35Ni) content, corresponding to two major stainless steels (304 and 330, respectively). Sintering during hydrogen reduction entraps small amounts of Cr2O3 particles (<1.1 vol %) while also leaving residual porosity, which can be eliminated in a subsequent step via remelting or forging. The forging case demonstrates a fully solid-state path, from ore to part, with the following benefits: (i) no melting or solidification, (ii) low energy footprint, (iii) low CO2 footprint, and (iv) high material utilization.