Microstructure and Mechanical Properties of High-Co Maraging Steel Fabricated by Metal Powder Injection Molding

Currently, systematic understanding of strengthening and embrittlement mechanisms in high-Co maraging steels fabricated by metal powder injection molding (MIM) is lacking. In this study, a high-Co maraging steel (Fe–13.2Co–7.7Cr–6.9Ni–6.6Mo–0.2Nb–0.008C) was prepared by MIM, and the effects of processing parameters and heat treatment on its microstructure and mechanical properties were systematically investigated. Sintering at 1370 °C for 2 h yielded a relative density of 95.93 ± 0.16%. The as-sintered specimens exhibited a lath martensite matrix containing pores, Si-rich oxide particles, and Mn–Cr-rich oxide particles. A solution treatment at 1000 °C for 1 h followed by water quenching produced supersaturated martensite, but residual stresses likely contributed to the reduced ductility. After aging at 540 °C for 4 h, a high dislocation density remained and provided dislocation strengthening, while nanoscale C14 Laves and μ phases precipitated and may contribute to the high strength. The solution-treated and aged specimens demonstrated high strength but limited ductility, with an ultimate tensile strength (UTS) of 1762 ± 44 MPa, a yield strength (YS) of 1699 ± 23 MPa, an elongation at break (ɛ) of 1.3 ± 0.2%, and a microhardness of 554.7 ± 10.5 HV0.5. The limited ductility may have resulted from the coupled detrimental effects of pores, inclusions, and the hardened matrix.