Patent ID: 8789817

Claim:
A steel alloy comprising, in terms of percent by mass: 0.47 to 0.49% C; 2.10 to 2.40% Si; 0.40 to 0.50% Mn; 0.20 to 0.30% Cr; 0.40-0.60% Ni; 0.05-0.20% Mo and 0.05-0.20% V; the balance being substantially Fe and incidental elements and impurities, and wherein the following formulas (6)-(8) are satisfied: 0.730%≦C(%)+Mn(%)/6+Si(%)/24+Ni(%)/40+Cr(%)/5+Mo(%)/4+V(%)/14≦0.780% (6); 0.630%≦C(%)+Mn(%)/6+Si(%)/24≦0.670% (7); and 1.35%≦Si(%)−0.46C(%)−1.08Mn(%) (8).