STEEL WIRE, METHOD FOR MANUFACTURING STEEL WIRE, METHOD FOR MANUFACTURING SCREW OR BOLT USING STEEL WIRE AND SCREW OR BOLT MANUFACTURED USING STEEL WIRE

摘要

PROBLEM TO BE SOLVED: To manufacture screws or bolts excellent in hardness and ductility using a steel wire as a raw material without applying any heat treatment or surface treatment, as well as to prevent a problem that the working life of tools is shortened due to work-hardening which occurs when screws or bolts are manufactured by processing a steel wire.;SOLUTION: A steel wire having a carbon content of 0.06 mass% or less, a tensile strength of 800-1,220 MPa, a reduction area of 70% or more, Vickers hardness of 250-435, an average crystal particle diameter of a ferrite structure of 5 μm or less in a cross section vertical to the longitudinal direction is used as the raw material, and the steel wire is processed to manufacture screws or bolts having a strength ranking of 8.8 (tensile strength of 800 MPa, and a yield load of 640 MPa) to 12.9 (tensile strength of 1,220 MPa, and a yield load of 1,100 MPa). The steel wire is manufactured by work-hardening of a steel wire material having a carbon content of 0.06 mass% or less through wire drawing so that the reduction of area is 85-99% and/or through rolling so that the reduction of area is 93-99%.;COPYRIGHT: (C)2012,JPO&INPIT