Single-step reductive sintering for sustainable additive manufacturing of as-water-atomized steel powders

Steel additive manufacturing (AM) has traditionally relied on highly refined powders that underwent energy-intensive pre-processing to remove impurities and achieve the targeted bulk composition. This study presents an innovative, resource-efficient, and economically viable approach to binder jet additive manufacturing (BJAM) of steel. By directly utilizing low-cost, as-water-atomized steel powders, this method achieves in-situ chemical refinement and bulk densification via a single-step reductive sintering process, streamlining production while minimizing environmental impact and costs. Key factors include maintaining low H₂ partial pressure to prevent excessive decarburization, while leveraging higher temperatures to reduce stable oxides and triggering supersolidus liquid-phase sintering (SLPS), thus achieving densification > 99.7 % solid. In-situ thermal and off-gassing analyses, combined with ex-situ chemical analysis, revealed the underlying reductive sintering mechanisms, particularly the dominant role of CO-based redox reaction in driving deoxidation and decarburization after the BCC→FCC transformation.