| 摘要 |
PROBLEM TO BE SOLVED: To produce a strip having high quality by directly casting the strip from molten steel, hot-rolling this strip online, executing the first forcible cooling at a specified cooling speed, executing the successive forcible cooling to interrupt the transformation after holding the strip for a time needed to develop the bainitic transformation at a specified temperature and coiling at a lower temperature than a specified temperature. SOLUTION: The strip having 0.5-10 mm thickness is directly cast from the molten steel and this strip is passed through one or more times in 25-70% working ratio at higher temperatures than the Ac3 temperature of the steel online to execute the hot-rolling, and the first forcible cooling of the strip is executed at 5-100 deg.C/sec cooling rate. This strip is held for the time needed to develop the bainitic transformation having more than 5% of the retained austenite content and at 550-400 deg.C, and the formation of the pearlite is prevented and, successively, the second forcible cooling is executed to interrupt the transformation by lowering to <=400 deg.C, and the strip is coiled at <=350 deg.C.
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