Abstract: 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 PS3 ?m, and an average grain size of a bainite block in a third center portion of the steel wire is set to PC3 ?m, the PS3 satisfies Expression (c), and the PS3 and the PC3 satisfy Expression (d), a standard deviation of a grain size of the bainite block in the structure is less than or equal to 8.

Abstract: 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 PS3 ?m, and an average grain size of a bainite block in a third center portion of the steel wire is set to PC3 ?m, the PS3 satisfies Expression (c), and the PS3 and the PC3 satisfy Expression (d), a standard deviation of a grain size of the bainite block in the structure is less than or equal to 8.

Abstract: A wire rod according to the present invention includes a predetermined chemical composition, wherein a metal structure includes 90 area % to 100 area % of bainite, wherein when eight test pieces having a length of 400 mm, which are obtained by dividing a wire rod having a length of 3200 mm into eight components having a same length, are manufactured, an average tensile strength TS of each test pieces satisfies a relation of “[TS]?810×[C]+475” by N/mm2, wherein a difference between a maximum value and a minimum value of the tensile strengths of each test pieces is 50 N/mm2 or less, and wherein an average reduction of area RA of each test pieces satisfies a relation of “[RA]??0.083×[TS]+154” by %.