| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel for forging, in which dispersion of a fatigue characteristic (specifically, endurance limit ratio) is surely suppressed.SOLUTION: The steel for forging includes 0.2-0.6% (mass%) C, 0.05-0.50% Si, 0.20-1.5% Mn, 0.10-3.50% Ni, 0.9-4% Cr, 0.10-0.70% Mo, 0.01-0.20% V, 0.005-0.10% Al, 0.008% or less (not including 0%) S, 0.005% or less (not including 0%) Ti and 0.0025% or less (not including 0%) Total O, with the balance being iron and inevitable impurities. The ratio of the number of oxide inclusions whose CaO content is 5 to 45 mass% to the number of all the inclusions observed on a steel cross section is 5% or more, and a major diameter of the maximum inclusion observed on the steel cross section is 100 μm or shorter. |
