Patent ID: 7618498

Claim:
A steel obtained by hot rolling, at a starting temperature of 1500° C. to 1250° C., a steel composition comprising: 0.35 to 0.65 percent by mass of C, 1.4 to 2.5 percent by mass of Si, 0.1 to 1.0 percent by mass of Mn, 2.0 percent by mass or less (exclusive of 0 percent by mass) of Cr, 1.0 percent by mass or less (exclusive of 0 percent by mass) of Ni, 1.0 percent by mass or less (exclusive of 0 percent by mass) of Cu, 0.020 percent by mass or less (exclusive of 0 percent by mass) of P, 0.020 percent by mass or less (exclusive of 0 percent by mass) of S, 0.006 percent by mass or less (exclusive of 0 percent by mass) of N, and 0.1 percent by mass or less (exclusive of 0 percent by mass) of Al, with the remainder being iron and inevitable impurities, cooling the hot rolled steel composition, from a starting temperature of 900-1050° C., to 650° C. at an average rate of 2-20° C./sec, and holding the cooled steel composition at 580-650° C. for 100-1200 seconds, wherein Wp(Fe) and W(C) satisfy the following condition: Wp(Fe)>5×W(C), wherein Wp(Fe) is the content of Fe (percent by mass) constituting Fe-containing precipitates in the steel; and W(C) is the carbon content (percent by mass) of the steel; and the steel obtained has a tensile strength of 1900 MPa or more.