Regulating κ-carbides within B2/D03 reinforcing skeleton via short-term aging to enhance wear resistance of LDED-processed low-density steel coating

To optimize the wear performance of low-density steels under service conditions across a wide temperature range, Fe-29Mn-13Al-5Ni-1.2C low-density steel coatings were fabricated via laser directed energy deposition (LDED), followed by a two-step heat treatment consisting of annealing and aging. The effect of aging time on the microstructure, hardness, and tribological behavior was systematically investigated. Compared with conventional aging treatments lasting tens of hours, the high concentration of non-equilibrium vacancies introduced by LDED enables short-term aging to significantly accelerate the precipitation of κ-carbides in the low-density steel. The results indicate that after aging for 120 min, fine and dense nanoscale κ-carbides with a size of approximately 15-35 nm are formed within the coating. Together with the dual-morphology B2 and D0 3 phases formed after annealing, they provide a synergistic strengthening effect, leading to a coating hardness of ∼544 HV 0.5 and the lowest wear rates at both room temperature and 550 °C, which are 5.264 × 10 −5 mm 3 N −1 m −1 and 0.228 × 10 −5 mm 3 N −1 m −1 , respectively. When the aging time is prolonged to 240 min, the κ-carbides coarsen significantly, and submicron-scale carbides appear at grain boundaries, resulting in a decrease in hardness. Meanwhile, the coarse κ-carbides tend to detach and cause severe three-body abrasive wear, leading to increased fluctuation of the friction coefficient and degraded wear resistance. This study reveals the precipitation mechanism of κ-carbides during aging of LDED-processed low-density steels and provides an important theoretical basis for designing low-density steel coatings that combine lightweight characteristics with excellent wear performance.