Sustainable Fe–Cr–Ni Stainless Steels via Hydrogen Reduction of Blended Oxides
Maryam Al-Buainain, David C. Dunand
Abstract
Hydrogen reduction of iron oxide is a promising solid-state, moderate-temperature steelmaking approach with no direct CO 2 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 Fe 2 O 3, NiO, and Cr 2 O 3 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 Cr 2 O 3 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 CO 2 footprint, and (iv) high material utilization.