Synergistic Enhancement of Strength and Ductility of Maraging Steel Via Nanometer-Scaled Microstructures

Maraging steels with ultra-high strength and good ductility were usually achieved via semi-coherent nanometer-sized precipitates and a dual-phase structure. In this study, a new cobalt-free maraging steel with high strength (1866 MPa) and satisfactory tensile elongation (11.5%) at room temperature was developed. The nano-scaled precipitates in the martensite matrix were analyzed, in which the η-Ni 3 (Ti, Mo) precipitates distributed in a width of 5.4 nm and a length of 19 nm. The needle-like Ni 3 Ti and spherical Mo-enriched phase made a predominant contribution to enhancing the strength of the maraging steel, while the ductility can be attributed to the nano laminated austenite structure, which could effectively prevent the propagation of microcracks in the martensite matrix. It was found that the nucleation of precipitates was prevalently originated at dislocations and martensite boundaries, and thus, a heterogeneous microstructure of precipitates was formed. Besides, the size and number of precipitates could be regulated by tuning the heat treatment conditions, in which a finer size and a larger number of precipitates could be gained by annealing at a high temperature for a short time