Abstract: By transmission electron microscope, hardenss test and instrumented impact test, the effect of aging process on microstructure and properties of precipitation-hardening stainless steel FV520(B) is investigated. The results show that the most precipitate of FV520(B) steel is copper-rich phase ε-Cu. The maximum hardness is reached after FV520(B) ages at 420 ℃, due to the coherent precipitation of fine copper particles. However, the hardness of FV520(B) aged at higher than 420 ℃ gradually decreases , due to the ε-Cu precipitating and coarsening, the matrix recrystallizing. Toughness of FV520(B) at different aging temperatures is dependent on the crack propagation energy. The effect of aging microstructure on impact crack initiation energy is less, but the effect of that on crack propagation energy is great. As FV520(B) aged at 420 ℃ and 600 ℃, its toughness is the worst and best respectively. The fracture appearance of the impact specimens aged at 420 ℃ and 470 ℃ mostly is in form of cleavage, which of the specimens aged at other temperature mostly in form of dimple, but the dimples have nice difference.

Key words: Aging treatment, Instrumented impact test, Microstructure, Precipitation-hardening