| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a soft steel material which has no decarburized layer in a surface layer, a soft structure, little strength dispersion and superior cold workability, in as hot-rolled state. SOLUTION: The manufacturing method comprises heating a steel slab having a predetermined chemical composition at 850 to 1,250°C; rough-rolling and intermediate-rolling it at 730°C or higher; rolling it at least once in the temperature range lower than 850°C, with an area reduction of 10% or higher and a pass-to-pass period of 30 seconds or shorter before the next pass; and finish-rolling it in the conditions of the total area reduction of 30% or higher and the temperature of a rolled material in the appearance side of a finish rolling machine of 800 to 950°C. The manufacturing method further comprises temporarily rapidly cooling it to the temperature range between an Ms point and 650°C shown in the drawing, just after finish rolling; winding it up with a winding machine; recuperating the ring-shaped material to 650 to 750°C; and subsequently slowly cooling it to 500°C at the hottest from the temperature range at a cooling rate of 0.01 to 0.75°C/second. A period between the end of finish rolling and the start of slow cooling is preferably set to 25 seconds or longer. COPYRIGHT: (C)2005,JPO&NCIPI
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