2. Microstructural Aspects of High-Strength Maraging Steel Fracture Toughness Enhancement

The results of phase composition, microstructure, mechanical properties, and characteristics of static and dynamic fracture toughness study as well as specimens’ surface fractographic analysis for more than 20 experimental and industrial Fe-Ni-Co-Mo-Ti-, Fe-Ni-Mo-Ti-, and Fe-Cr-Ni-Mo-Ti-based high-strength maraging steels are presented. The influence of maraging steel metallurgical production technology, their heat and thermal-mechanical treatment, and level of alloying elements forming the reinforcing intermetallic particles is highlighted. Main microstructural opportunities of crack resistance and structural strength enhancement of the studied steels by adjusting the volume fraction and morphology of intermetallic, austenitic grain size, providing microstructure with metastable retained and reverted austenites, and eliminating the embrittlement effect of grain boundary carbonitride particles are defined. It is shown that the ratio of the named factor contribution considerably depends on the achieved level of high-strength maraging steel fracture toughness.