12Cr1MoV round steel (GB/T 3077) is designed for high-temperature service, with 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% phosphorus (P), and ≤0.035% sulfur (S).
Three elements drive its high-temperature chemical stability: chromium, molybdenum, and vanadium. Chromium (0.90–1.20%) forms a dense, stable Cr₂O₃ oxide layer that resists oxidation at temperatures up to 550°C-preventing the steel from reacting with oxygen in high-temperature environments. Molybdenum (0.25–0.35%) improves creep resistance (resistance to slow deformation under heat and pressure) by slowing the diffusion of atoms within the steel, which reduces the rate of carbide coarsening (a process that weakens high-temperature performance). Vanadium (0.15–0.30%) forms fine vanadium carbides (VC) that pin grain boundaries, preventing grain growth at high temperatures and maintaining chemical uniformity. Carbon (0.08–0.15%) is kept low to avoid excessive carbide formation, which would make the steel brittle at high temperatures, while silicon and manganese act as deoxidizers to minimize oxide inclusions.