| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a high carbon steel plate production method by which even for a high carbon steel plate having a thickness of≥5 mm, a uniform structure is obtained in every area in the thickness direction of the steel plate in a hot rolling stage, pro-eutectoid ferrite is not generated, consequently the high carbon steel plate is produced which is hardly cracked at a blanked end face and is excellent instretch-flange formability. <P>SOLUTION: A steel plate of a thickness of≥5 mm after hot rolled and containing 0.2-0.7 mass % C is hot-rolled at the finish temperature (Ar<SB>3</SB>transformation point -20°C) or above, then intensive cooling with the cooling speed of≥150°C/sec. is applied to a surface layer part and a thickness central part of the steel plate under the cooling condition that the minimum temperature of the surface layer part during the intensive cooling is≥350°C, the intensive cooling stop temperature is 450-570°C, and the structure of the steel plate when the transformation is started is the same between the surface layer part and the thickness center part of the steel plate. In addition, the temperature from the intensive cooling stop to the coiling is in a range of 450-570°C, and the steel plate is kept in the temperature range in which the structure of the steel plate when the transformation is started is not changed. <P>COPYRIGHT: (C)2005,JPO&NCIPI</p> |
