AISI 4340 steel has poor corrosion resistance.
The chromium content of 4340 steel is only 0.70%-0.90%, far lower than the stainless steel standard (10.5%). Therefore, it cannot form a dense passivation protective film, making it prone to rusting in humid, acidic, and alkaline environments.
The core value of 4340 steel lies in its unparalleled comprehensive performance of strength, toughness, and fatigue resistance, rather than its corrosion resistance.