Synergistic effects of mechanical milling and annealing on the microstructural evolution and hardness of Fe–C alloy powders

Fe-C alloys provide high strength and hardness, enabling broad use in structural, automotive, and tooling applications. This study examines the coupled effects of mechanical milling duration (4, 8, and 12 h) and annealing temperature (400, 500, and 600 °C) on the microstructural evolution, phase behavior, elemental distribution, and hardness of Fe-C powders. This study produces powders via high-energy ball milling and performs controlled annealing. It characterizes microstructures with optical microscopy and Scanning Electron Microscopy (SEM), maps elemental distributions by Energy Dispersive X-ray Spectroscopy (EDS), and evaluates hardness using Brinell Hardness Number (BHN). Prolonged milling (12 h) refined grains to the ultrafine regime, whereas annealing at 600 °C promoted grain coarsening and surface oxidation. EDS mapping indicated carbon segregation at 400 °C and oxygen enrichment at 600 °C, consistent with carbide formation and oxidation, respectively. Milling for 12 h followed by annealing at 400 °C produced the highest hardness (320 BHN) by promoting nanostructuring and dislocation strengthening. Overall, coordinated control of milling and annealing enables tunable microstructures and properties in Fe-C alloys, informing the design of automotive components, sintered gears, and metal-matrix composites.