Steel for Machine Structural Use

A steel for machine structural use having a chemical composition consisting of, in mass %:

• C:
• 0.15 to less than 0.30%,
• Si:
• 0.01 to 0.80%,
• Mn:
• 0.20 to 2.00%,
• P:
• 0.030% or less,
• S:
• 0.010 to 0.100%,
• Pb:
• 0.010 to 0.100%,
• Al:
• 0.010 to 0.050%,
• N:
• 0.015% or less,
• O:
• 0.0005 to 0.0030%,
• Cr:
• 0.50 to 2.00%,
• Ni:
• 0 to 3.50%,
• B:
• 0 to 0.0050%,
• V:
• 0 to 0.70%,
• Mo:
• 0 to 0.70%,
• W:
• 0 to 0.70%,
• Nb:
• 0 to less than 0.050%,
• Cu:
• 0 to 0.50%,
• Ti:
• 0 to 0.100%, and
• Ca:
• 0 to 0.0030%,
• with the balance being Fe and impurities, the chemical composition satisfying Formula (1),
• wherein, in the steel, a total number of specific inclusions which are any of MnS inclusions, Pb inclusions and composite inclusions containing MnS and Pb, and which have an equivalent circular diameter of 5 μm or more is 40 per mm2 or more;
• Mn/S≥8.0 (1)
• where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1).