Effect of Aging Temperature on the Corrosion Resistance of a 2.2 GPa Ultra-high-strength Steel Designed Based on a Hybrid Concept

A novel ultra-high-strength steel was designed using a hybrid green low-carbon alloy concept, which integrates multiple steel grades to achieve ultra-high strength and good corrosion resistance. The influence of aging temperature on its corrosion resistance was systematically investigated. The results showed that aging temperature had no significant effect on the types of corrosion products. These corrosion products were mainly composed of FeCr 2 O 4 , α-(Fe, Cr)OOH, γ-FeOOH, and Fe 3 O 4 /Fe 2 O 3 . However, the corrosion resistance deteriorated progressively with the increase in aging temperature. This decline is mainly due to the dislocation density from 3.76×10 16 m -2 to 2.76×10 16 m -2 as the aging temperature increased from 500 °C to 620 °C. The reduced dislocation density decreased the number of corrosion-active sites and delayed the formation of the passivation film. Concurrently, the increased precipitation of Cr 23 C 6 expanded the poor-Cr regions, further weakening corrosion resistance. The experimental steel exhibited highest tensile strength after aging at 540 °C, with a tensile strength of 2256 MPa and an elongation after fracture of 9.2%. Therefore, aging at 540 °C for 8 hours is identified as the optimal process for balancing mechanical properties and corrosion resistance in this steel. This provides insights for the development of new ultra-high strength steel with "structural and functional integration" for applications in aircraft landing gear, high-end bearings, and other areas requiring both ultra-high strength and high corrosion resistance.