12Cr2Mo1VTiB 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), 2.00–2.50% chromium (Cr), 0.90–1.10% molybdenum (Mo), 0.25–0.35% vanadium (V), 0.08–0.15% titanium (Ti), 0.002–0.006% boron (B), ≤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, no Ti/B), 12Cr2Mo1VTiB has three key upgrades: higher chromium (2.00–2.50% vs. 0.90–1.20%), added titanium (0.08–0.15%), and added boron (0.002–0.006%)-these improve high-temperature stability via:
Enhanced oxidation resistance: Higher chromium forms a thicker, more stable Cr₂O₃ passive layer that resists breakdown at temperatures up to 600°C (vs. 550°C for 12Cr1MoV). This prevents the steel from reacting with oxygen and forming iron oxides that weaken the structure.
Titanium carbide stabilization: Titanium forms fine titanium carbides (TiC) that are more stable at high temperatures than vanadium carbides (VC) in 12Cr1MoV. TiC resists coarsening (growing larger) at elevated temperatures, maintaining their ability to pin dislocations and strengthen the steel.
Boron grain boundary strengthening: Boron (0.002–0.006%) segregates at grain boundaries, reducing the diffusion of atoms across boundaries and slowing creep (slow deformation under heat/pressure). Boron also enhances the stability of the austenitic phase, preventing the formation of brittle martensite during thermal cycling.
Molybdenum and vanadium function similarly to 12Cr1MoV, but the added elements extend the steel's high-temperature service range by 50–100°C.