Direct and sustainable stainless steelmaking from nickel and chromite ores by hydrogen plasma smelting reduction

Stainless steel, known for its exceptional properties and diverse applications, conventionally requires a multistage process that generates considerable CO₂ emissions by using fossil-based carbon reductants. This study investigated hydrogen plasma smelting reduction as a novel, sustainable, and efficient method for producing stainless steel directly from lateritic nickel and chromite ores. The research aimed to examine the effect of ore proportion on AISI 300 series stainless steel production and assess the reduction process over time through thermochemical calculations and experimental studies. Results showed that increasing the proportion of chromite ore in the feed raises Cr content and reduces Ni content in metals while increasing Cr₂O₃ and Al₂O₃ content in oxides. A briquette comprising 30wt% chromite ore and 70wt% calcined nickel ore yields better results for AISI 300 stainless steel, with Fe, Cr, Ni, and Si content of 62.95wt%, 19.37wt%, 11.83wt%, and 0.72wt%, respectively, after 180 s of hydrogen plasma exposure. Nearly all NiO compounds are converted into Ni after 60 s of smelting reduction, whereas FeO compounds are almost fully converted into Fe after 120 s of smelting reduction. AISI 300 series stainless steel is successfully produced after 120 s of reduction, achieving Fe, Cr, Ni, and Si content of 64.36wt%, 21.92wt%, 10.08wt%, and 0.61wt%, respectively. Process optimization remains promising because the Cr₂O₃ content in the slag is still relatively high at 15.52wt%. This ultrafast and direct production method holds considerable potential to transform stainless steel production by reducing environmental impact and enhancing process efficiency. Specifically, the method eliminates the use of an argon oxygen decarburization converter and vacuum oxygen decarburization in stainless steelmaking.