ROLLED STEEL BAR FOR HOT FORGING

摘要

A rolled steel bar for hot forging having a chemical composition consisting, by mass percent, of C: 0.27 to 0.37%, Si: 0.30 to 0.75%, Mn: 1.00 to 1.45%, S: 0.008% or more and less than 0.030%, Cr: 0.05 to 0.30%, Al: 0.005 to 0.050%, V: 0.200 to 0.320%, and N: 0.0080 to 0.0200%, the balance being Fe and impurities, wherein the contents of P, Ti and O in the impurities are, by mass percent, P: 0.030% or less, Ti: 0.0040% or less, and O: 0.0020% or less; and Y1 expressed by the following formula <1> is 1.05 to 1.18.
where, C, Si, Mn, Cr, V, and S in the above formula <1> represent, respectively, the content by mass percent of each of the elements. A hot-forged part having a tensile strength of 900 MPa or higher and a transverse endurance ratio of 0.47 or higher after hot forging can be obtained by the rolled steel bar.