Production manner null of wire rod and its production manner and high intensity non quality check upset head bolt for high intensity non quality check upset head bolt

摘要

PROBLEM TO BE SOLVED: To provide a rod used for manufacturing an upset head bolt superior in delayed fracture resistance, in spite of having as high or higher tensile strength as 900 N/mm² after the rod in as-hot-rolled state is draw-treated and cold-forged.;SOLUTION: The rod comprises is a two-phase structure of pearlite and ferrite, of which the ferrite fraction is 30-70% by area rate. Furthermore, an average particle size of carbides/nitrides in the ferrite is controlled to be 50 nm or less, and the number of carbides/nitrides with average sizes of 50 nm or less is controlled to be 50/μm² or more.;COPYRIGHT: (C)2003,JPO