| abstract |
A steel bar according to an embodiment of the present invention is a steel bar having a predetermined chemical composition, a quenching in the cross section of 1.5 mm or less,? Max and? Min of 1.5 mm or less, and a structure in the surface layer region of 10% And a balance comprising at least one of bainite and martensite, wherein an average value of the particle diameters on bcc in the surface layer region is 1.0 to 10.0 占 퐉, and an average value of the particle diameters on bcc in the central region The hardness of a portion having a depth of 50 mu m from the surface is HV 200 to 500, and the total decarburized layer depth DM-T is 0.20 mm or less. |