60Si2CrVA round steel (GB/T 1222) has a composition of 0.56–0.64% carbon (C), 1.60–2.00% silicon (Si), 0.40–0.70% manganese (Mn), 0.40–0.70% chromium (Cr), 0.10–0.20% vanadium (V), ≤0.025% P, ≤0.025% S.
Compared to 60Si2CrA (0.56–0.64% C, 1.60–2.00% Si, 0.40–0.70% Mn, 0.40–0.70% Cr, no V, ≤0.030% P/S), the addition of vanadium (0.10–0.20%) and tighter impurity limits make 60Si2CrVA more fatigue-resistant:
Vanadium's grain refinement and carbide strengthening: V forms ultra-fine VC carbides that pin austenite grain boundaries during heat treatment, resulting in a finer grain structure (ASTM 11–12 vs. ASTM 9–10 for 60Si2CrA). Fine grains have more boundaries to block fatigue crack propagation-cracks require 2–3x more energy to move across fine grains. VC also acts as a "micro-barrier" to dislocation movement during cyclic loading, reducing plastic deformation that initiates cracks.
Tighter P/S limits (≤0.025% vs. ≤0.030%): Lower phosphorus and sulfur reduce the formation of brittle inclusions (Fe₃P, FeS) that act as fatigue crack initiators. In 60Si2CrA, these inclusions can reduce fatigue life by 20–30%, but 60Si2CrVA's ultra-low impurities minimize this risk.
Silicon and chromium remain the primary strengtheners, but vanadium optimizes the microstructure to maximize fatigue resistance-critical for steels in high-cycle fatigue service.