ROD MATERIAL FOR NON-TEMPERED MACHINE COMPONENT, STEEL ROD FOR NON-TEMPERED MACHINE COMPONENT, AND NON-TEMPERED MACHINE COMPONENT

摘要

A steel wire for a non heat-treated mechanical part includes, as a chemical composition, by mass%, a predetermined amount of C, Si, Mn, Cr, Mo, Ti, Al, B, Nb, and V, and limited P, S, N, and O and a remainder of Fe and impurities; in which a structure includes, by volume%, a bainite of greater than or equal to 75×[C%]+25, and a remainder of one or more of a ferrite and a pearlite when an amount of C is set to [C%] by mass%; when an average aspect ratio of a bainite block in a second surface layer area of the steel wire is set as R1, the R1 is greater than or equal to 1.2; when an average grain size of a bainite block in a third surface layer area of the steel wire is set to P_S3 µm, and an average grain size of a bainite block in a third center portion of the steel wire is set to P_C3 µm, the P_S3 satisfies Expression (c), and the P_S3 and the P_C3 satisfy Expression (d), a standard deviation of a grain size of the bainite block in the structure is less than or equal to 8.0 µm; and a tensile strength is in a range of 800 MPa to 1600 MPa, ${\mathrm{P}}_{\mathrm{S}\mathrm{3}}\le \mathrm{20}/\mathrm{R}\mathrm{1}\mathop{\mathrm{image}}$${\mathrm{P}}_{\mathrm{S}3}/{\mathrm{P}}_{\mathrm{C}3}\le \mathrm{0.95}\mathop{\mathrm{image}}$