| 摘要 |
PURPOSE: To produce a cold rolled steel sheet for working, combining workability, aging resistance, and blankability. CONSTITUTION: A steel, having a composition consisting of, by weight, 0.01-0.04% C, <=0.04% Si, 0.1-0.3% Mn, <=0.02% P, 0.003-0.015% S, 0.01-0.1% sol.Al, <=0.005% N, and the balance Fe with inevitable impurities, is hot-rolled, coiled at 600-750 deg.C, pickled, cold-rolled at >=60% draft, and annealed continuously. At the time of annealing, the resulting sheet is soaked at a temp. between the recrystallization temp. and the Ac3 point for >=30sec, cooled slowly to 600-650 deg.C at a rate of <=30 deg.C/s, cooled rapidly to 300-400 deg.C at a rate of 50 to 150 deg.C/s, and then subjected, after this rapid cooling without delay or after reheating, to overaging under the conditions of 350-400 deg.C overaging starting temp., 250-300 deg.C overaging finishing temp., and 180-420sec overaging time in the range between tA and tB(sec), where tA and tB are represented, respectively, by equations, tA=(ultimate rapid cooling temp. -250)×2.4 and tB=tA+180.
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