12CrMoV round steel (GB/T 3077) has a composition of 0.08–0.15% carbon (C), 0.17–0.37% silicon (Si), 0.40–0.70% manganese (Mn), 0.90–1.20% chromium (Cr), 0.25–0.35% molybdenum (Mo), 0.15–0.30% vanadium (V), ≤0.035% P, ≤0.035% S.
Compared to 12Cr1MoV (0.08–0.15% C, 0.17–0.37% Si, 0.40–0.70% Mn, 0.90–1.20% Cr, 0.25–0.35% Mo, 0.15–0.30% V), the two grades are nearly identical in composition-their key difference lies in vanadium content control: 12CrMoV has a tighter V range (0.20–0.25% vs. 12Cr1MoV's 0.15–0.30%), which optimizes moderate-temperature (450–550°C) creep resistance.
Vanadium forms VC carbides that pin dislocations and grain boundaries-critical for resisting creep. 12CrMoV's tighter V range ensures VC carbides are uniformly sized (10–20 nm) and dispersed, avoiding the coarse VC particles that form in 12Cr1MoV when V is at the upper end of its range. Coarse VC particles are less effective at pinning dislocations, reducing creep resistance. By controlling V to 0.20–0.25%, 12CrMoV maintains consistent VC size and distribution, resulting in a 20–25% lower creep rate at 500°C than 12Cr1MoV with variable V content.