Carbon: C, 0.47 ~ 0.53, silicon: Si 0.15 ~ 0.35, Mn: Mn 0.60 to 0.90, phosphorus: P ≤ 0.030, sulfur: S ≤ 0.035, the copper: Cu ≤ 0.30, Ni: Ni ≤ 0.20, Cr: Cr ≤ 0.20 . 


 Mechanical properties 
 Tensile strength σb (MPa): ≥ 630 (64) yield strength σs (MPa): ≥ 375 (38) elongation δ5 (%): ≥ 14 Reduction of area ψ (%): ≥ 40 impact energy Akv (J ): ≥ 31 (4) impact the toughness the value αkv (J/cm2): ≥ 39 (4) Hardness: heat treatment, ≤ 241HB; annealed steel, ≤ 207HB sample size: sample size of 25mm