| 摘要 |
PURPOSE:To manufacture high tensile steel excellent in strength, workability and ductility by hot-rolling steel contg. Mn or furthermore Cr and making the composition contg. retained austenite of specified quantity. CONSTITUTION:A billet contg. 0.15-0.80% C, 1.0-3.0% Si and 0.5-3.0% (Mn+ Cr) is hot-rolled to make a steel sheet and after water cooling, the steel sheet is wound as a hot rolled coil and cooled in air. By contg. Mn or Cr wherein stable austenite is formed through substituting Cr for Mn, the quantity of retained austenite contained in the system is >=5% and the balance consists of bainite contg. >=1.0% fine ferrite of <=5mu average grain size and high tensile steel sheet excellent in strength, workability and also ductility is obtained.
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