Patent ID: 7074283

Claim:
A low alloy steel, characterized by consisting of, by mass %, C: 0.2â€“0.55%, Si: 0.05â€“0.5%, Mn: 0.1â€“1%, S: 0.0005â€“0.01%, O(Oxygen): 0.0010â€“0.01%, Al: 0.005â€“0.05%, Ca: 0.0003â€“0.007%, Ti: 0.005â€“0.05%, Cr: 0.1â€“1.5%, Mo: 0.1â€“1% and Nb: 0.005â€“0.1%, and the balance Fe and impurities; and also characterized by the impurities whose contents are restricted to Pâ‰¦0.03% and Nâ‰¦0.015%; and further characterized by containing composites of inclusions of not greater than 7 Î¼m in major axis with an appearance frequency of not less than 10 pieces of composites per 0.1 mm 2 of the steel cross section, wherein the composite comprises an outer shell of carbonitride of Ti and/or Nb surrounding a nucleus of oxysulfide of Al and Ca.