| 摘要 |
PURPOSE:To improve the longitudinal crack resistance of a high r value hot rolled steel sheet, by adding specific ratios of B and Ca independently or in combination to a dead soft C-Al killed steel having a specific compsn. added with Ti and Nb alone or in combination. CONSTITUTION:The steel which contains, by weight, <=0.013% C, 0.05-0.35% Mn, <=0.03% S, <=0.02% P, 0.005-0.080% sol.Al, and 0.0005-0.005% B, is added with Ti or Nb at <=0.2% Ti and >=0.3% Nb and at such weight % as to attain formula I (where formula II) and consists of the balance Fe is used. While such steel is lubricated at 500-800 deg.C, the steel is rolled at 60-95% total draft and is then subjected to an annealing treatment or high-temp. coiling at 700-750 deg.C. The steel formed by incorporating 0.0005-0.01% Ca further into the above-mentioned steel and adding Ti and/or Nb at such weight % as to attain formula I (where formula III) may be used as well.
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