Achieving good ductility in 2.1 GPa grade maraging steel

Abstract

Maraging steels with ultrahigh strength are important for structural applications, but their low ductility severely limits engineering applications. Here we demonstrate improved ductility can be achieved in 0.18C10Ni8Co3Cr1.6Al1Mo1W maraging steel. This steel exhibits a high yield strength of 1.75 GPa, an ultrahigh tensile strength of 2.09 GPa and a uniform elongation of 5 %. Such good strength-ductility synergy arises from a unique microstructure: a refined hierarchical martensite matrix with dense coherent B2-nanoprecipitates. Strengthening models indicate that the ultrahigh strength can be attributed to block boundary strengthening, dislocation strengthening and precipitation strengthening. Utilizing transmission electron microscope coupled with geometric phase analysis at interrupted deformation stages, we reveal dynamic dislocation-nanoprecipitate and dislocation-dislocation interactions. Notably, mobile dislocations not only cut through nanoprecipitates but also penetrate pre-existing dislocation substructures and lath boundaries. Such deformation behaviors promote dislocation multiplication and accumulation, thereby conferring good strain hardening and ductility.