Effects of Solid–Solution Temperature on Microstructures and Mechanical Properties of 2200 MPa Grade Secondary Hardening Steel

With the increasing demands for mechanical properties of ultra-high-strength steels (UHSSs), enhancing their strength and obtaining an excellent strength-toughness matching have received widespread attention. In this paper, the influence of microstructure and primary carbides on the mechanical properties of 2200 MPa ultra-high-strength steel was studied by treating it at different solid-solution temperatures. The mechanical properties of the experimental steel following aging demonstrated a non-monotonic dependence on solid-solution temperature, manifested as an initial increase followed by a gradual decline in both strength and toughness. Microstructural evolution analysis reveals that elevated solid-solution temperatures induce coarsening of prior austenite and martensite grains in the steel, thereby promoting toughness enhancement. Concurrently, primary carbides progressively dissolve into the matrix with increasing solid-solution temperature, generating a supersaturated solid-solution that facilitates M₂C carbide precipitation during aging, ultimately leading to strength improvement in the experimental steel. An exceptional combination of strength, ductility, and toughness with an ultimate tensile strength of 2142 MPa, yield strength of 1830 MPa, elongation of 12.5%, and Charpy U-notch impact energy of 60.5 J was obtained when the experimental steel was solid-solution treated at 910 °C.