STEEL OF HIGH STRENGTH AND SUPERIOR IN COLD HEADING CHARACTERISTIC AND FASTENING PARTS SUCH AS SCREW AND BOLT OR FORMED ARTICLE SUCH AS SHAFT SUPERIOR IN STRENGTH

摘要

PROBLEM TO BE SOLVED: To provide a wire rod or a bar stock and steel including the wire rod or bar stock extensively which are free from the occurrence of a recess crack or similar defects even after worked into a steel wire or a steel bar then subjected to cold heading and form rolling or machining or working mainly comprising the machining without subjected to heat treatment thereby formed into fastening parts such as screws and bolts or formed articles such as shafts, and which have already desired high level strength in the stage of the steel wire or the steel bar without applying tempering processing to the fastening parts such as screws and bolts or the formed articles such as shafts formed by cold heading or the like.;SOLUTION: The steel for cold heading has a ferrite structure in which the volume fraction of cementite is 0% and a mean particle diameter is ≤1 μm in a cross section perpendicular to a rolling direction, the steel has mechanical properties of ≥600 MPa in tensile strength TS and ≥70% in reduction RA and is not subjected to spheroidizing annealing.;COPYRIGHT: (C)2010,JPO&INPIT