Rapid microwave sintering and microstructure evolution of non-magnetic (AISI 316L) and magnetic (AISI 410L) stainless steels: Differentiating the electric and magnetic field effects

• Microwave sintering of stainless-steel powders without compaction is investigated. • Single-mode microwave applicator enables targeted and efficient heating. • The H-field exhibits superior heating efficiency over the E-field in metal powders. • Magnetic stainless steel exhibits superior microwave heating efficiency over non-magnetic grades. • Rapid sintering is observed reaching 97.2 % (316L) and 98 % (410L) theoretical densities. • Microwave sintering is feasible for uncompacted powder and highly energy efficient. The consolidation of metal powders via sintering and melting is fundamental to advanced manufacturing, particularly metal additive manufacturing (AM). While laser and electron beams are established energy sources for powder consolidation in AM, their inherent energy intensity, high cost, and operational complexities limit wider adoption and accessibility. Microwave energy offers a potentially cheaper and more energy-efficient alternative, yet its suitability for the pressureless sintering of uncompacted metal powders, crucial for AM, remains unexplored. This study investigates the direct heating of uncompacted magnetic martensitic 410L and non-magnetic austenitic 316L stainless steel powders (D50 33 µm) using a 2.45 GHz single-mode microwave applicator. The feasibility of achieving high densities through pressureless microwave sintering is demonstrated, elucidating the distinct heating contributions of the electric (E-field) and magnetic (H-field) fields. Continuous monitoring of power absorption and apparent surface temperature allowed for precise energy consumption calculations. Uniquely, microwave heating achieved significant densification in uncompacted 410L (98 % theoretical density) and 316L (97.2 % theoretical density) within 4 min, consuming only 192 KJ. Post-sintering, Vickers hardness values were 633 ± 31 HV for 410L and 119.7 ± 22 HV for 316L. Ultimately, this work highlights microwave energy’s capability for rapid, high-performance processing of high-melting metals, establishing its viability as an alternative energy source for next-generation metal additive manufacturing.