| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of manufacturing a PC steel product excellent in spot weldability. SOLUTION: A billet or wire bar of a steel, having a composition consisting of, by weight, 0.1-0.4% C, 0.5-2.5% Si, 0.3-2.0% Mn, <=0.03% P, <=0.02% S, and the balance Fe with inevitable impurities, is heated to the austenite region and rolled into wire rod or steel wire. Immediately after the above rolling, the wire rod or steel wire is cooled rapidly down to 300 to 500 deg.C and held isothermally in the above temp. region for 5 to 150 sec, followed by rapid cooling without delay. The resultant steel product has a dual-phase structure consisting of martensite of <=25μm old austenite grain size, bainite, and >=2% retained austenite.
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