Influence of solid solution time on microstructure and precipitation strengthening of novel maraging steels

Abstract

Effective subsequent heat treatment is crucial for achieving the desired microstructure and excellent mechanical properties in laser-deposited high-performance maraging steel. In this paper, we systematically investigate the synergistic relationship and tuning mechanism of different solution treatment times on the microstructure-property synergy of new maraging steels fabricated using laser direct energy deposition (LDED). To determine the optimal heat treatment process, solution treatment was conducted at 840 °C for varying durations, followed by aging at 530 °C for 2 h to induce precipitation strengthening. The results indicate that after 2 h of solution treatment, the alloy exhibits optimal ductility with an elongation of 7.90 % ± 0.15 %, attributed to the refinement of the martensitic matrix and precipitated phases, along with the formation of a small amount of residual austenite. When the solution treatment time is extended to 4 h, the alloy achieves its highest tensile strength, reaching 1958 ± 24 MPa. However, the elongation decreases to 7.31 % ± 0.12 % due to the coarsening of the martensite and secondary phase particles. After 6 h of solution treatment, significant coarsening and aggregation of the martensite and Fe₂Mo intermetallic compounds markedly reduce the hardness, strength, and toughness of the alloy. By adjusting the solution treatment time, the size, morphology, and distribution of the martensitic matrix, Fe₂Mo, and nanoscale precipitated phases play a critical role in the strengthening and fracture processes. Therefore, optimizing the precipitation behavior of the martensitic matrix and Fe₂Mo intermetallic compounds through rational solution heat treatment is key to enhancing the mechanical properties of laser-deposited new maraging steels.