HIGH STRENGTH HOT ROLLED STEEL MATERIAL EXCELLENT IN WELDABILITY, AND HIGH STRENGTH STEEL WIRE AND HIGH STRENGTH BAR STEEL USING THE SAME

摘要

PROBLEM TO BE SOLVED: To combine excellent toughness, ductility, workability, and weldability by using a low carbon steel, having respectively specified Si and Mn contents, as a base and forming cross-sectional structure into specific mixed structure. ;SOLUTION: In a steel, 0.05-0.22% C, 0.5-2.0% Si, and 0.5-2.0% Mn by mass are incorporated and further, if necessary, one or more elements selected from the group consisting of ≤1.5% (not including 0%) Cr, ≤1.0% Mo, ≤0.5% Ti, ≤0.5% V, ≤0.01% B, and ≤0.1% Nb are incorporated. This steel material is hot-rolled and then subjected to controlled cooling. By this treatment, a mixed structure, in which the area ratio of (bainite + pearlite) comprises 10-95% of the cross-section structure and the balance consists of one or more kinds among ferrite, martensite, and retained austenite, is formed. By this method, the high strength hot rolled steel material, preferably having strength of an about 0.2% proof stress of ≥ about 800N/mm², can be obtained.;COPYRIGHT: (C)1998,JPO