| 摘要 |
PURPOSE: A production is provided to produce a strip having high quality by directly casting the strip from molten steel, hot-rolling the 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. CONSTITUTION: The strip having 0.5-10 mm thickness is directly cast from the molten steel and the 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. The 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 less than 400 deg.C, and the strip is coiled at 350 deg.C.
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