Progress on improving strength-toughness of ultra-high strength martensitic steels for aerospace applications: a review

Ultra-high strength steels are the crucial irreplaceable materials in the fields of aerospace, national defense and military industries. Unfortunately, it is challenging to achieve the requirements of vital components because of the strength-toughness trade-off of ultra-high strength steels. In this review, three types of conventional ultra-high strength martensitic steels are systematically summarized. These are: (i) low alloy ultra-high strength steels; (ii) ultra-high strength maraging steels; and (iii) Co–Ni secondary hardening steels. The main influencing factors of mechanical properties of ultra-high strength steels and the exploration on strengthening/toughening are discussed. In particular, the design concept based on the synergistic precipitation of low lattice misfit nano-particles and the formation of martensite matrix with high-density dislocations is a promising approach to develop novel ultra-high strength steels. Finally, some suggestions on the traditional design methods and future development of ultra-high strength steels are put forward and an outlook on future work is offered. This provides guidance for the development of novel ultra-high strength steels with excellent comprehensive performance.