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), ≤0.030% P, ≤0.030% S.
Compared to 60Si2MnA (0.56–0.64% C, 1.50–2.00% Si, 0.60–0.90% Mn, no Cr/V), 60Si2CrVA replaces manganese with chromium and vanadium, improving fatigue resistance via two mechanisms:
Chromium carbide refinement: Chromium (0.40–0.70%) forms fine, uniformly distributed Cr₇C₃ carbides instead of the coarser Mn₃C carbides in 60Si2MnA. Fine carbides pin dislocations more effectively and reduce stress concentrations-stress concentrations are the primary initiators of fatigue cracks. This makes 60Si2CrVA less prone to crack formation under repeated loading.
Vanadium grain refinement: Vanadium (0.10–0.20%) forms ultra-fine VC carbides that pin grain boundaries during heat treatment, resulting in a finer grain structure (ASTM 10–11 vs. ASTM 8–9 for 60Si2MnA). Finer grains increase fatigue resistance because grain boundaries act as barriers to crack propagation-cracks require more energy to move across multiple small grains than a few large ones.
Lower sulfur and phosphorus limits (≤0.030% vs. ≤0.035% in 60Si2MnA) further reduce fatigue crack initiation by minimizing brittle impurity inclusions.