Stainless steel synthesis from in-situ lunar resources via hydrogen reduction of chromite and meteoritic ferronickel alloying

Abstract

Future lunar settlements will require high-strength and high-toughness alloys made via in-situ resource utilization (ISRU) to mitigate mission costs. Here, we demonstrate a proof of concept for lunar ISRU-based fabrication of an Fe-Ni-Cr stainless steel through a combination of ferrochrome (Cr-36 wt% Fe) reduced from native chromite oxide minerals (FeCr2O4) and ferronickel (Fe-(5-15 wt%)Ni) from iron meteorites present in powder form within the lunar regolith. First, solid-state hydrogen reduction of synthetic chromite (FeCr2O4) is studied through in-situ X-ray diffraction and ex-situ metallography. Complete decomposition of chromite to Cr2O3 + Fe occurs after 15 min of isothermal reduction at 1200 °C, with ∼12 wt% of the Cr2O3 reducing to metallic Cr and incorporating into bcc-(Fe,Cr) solid solution after 1.5 h. Long-term isothermal ex-situ hydrogen reduction (12 h at 1200 °C) leads to full reduction of chromite into metallic ferrochrome. Second, this ferrochrome is arc-melted with Fe-9Ni-1Co (wt%) sourced from a Muonionalusta iron meteorite specimen to synthesize a homogeneous Fe-17Cr-6Ni-0.6Co (wt%) alloy with a composition close to low-carbon commercial stainless steel, a microstructure consistent with predictions based on conventional steels, and microhardness characteristics indicating good strength. This demonstration illustrates the viability of lunar stainless steel production which is fully reliant on ISRU.