| 摘要 |
This steel rod for a non-tempered machine component has a chemical composition comprising, in mass%, prescribed amounts of C, Si, Mn, Cr, Mo, Ti, Al, B, Nb and V, and has limited P, S, N and O, with the remainder comprising Fe and impurities; if the content of C, in mass%, is denoted as [C%], the structure includes at least 75 × [C%] + 25 vol% of bainite, with the remainder comprising at least one of ferrite and pearlite; if the average aspect ratio of a bainite block in a second surface layer section of the steel rod is denoted as R1, R1 is at least 1.2; if the average particle size of the bainite block in a third surface layer section of the steel rod is denoted as PS3 μm, and the average particle size of the bainite block in a third center section of the the steel rod is denoted as PC3 μm, PS3 satisfies formula (c), and PS3 and PC3 satisfy formula (d); the standard deviation of the particle size of the bainite block in the structure is not more than 8.0 μm; and the tensile strength is 800 MPa to 1600 MPa. (c) PS3 ≤ 20/R1 (d) PS3/PC3 ≤ 0.95 |
