| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing hot rolled TRIP steel small in the variation of the material in a coil, i.e., a highly workable hot rolled high tensile steel sheet excellent in material uniformity. SOLUTION: A slab having a steel composition containing 0.05 to 0.40% C, 1.0 to 3.0% Si, 0.6 to 3.0% Mn, <=0.3% Al and <=0.2% P and suitably containing one or more kinds among Cr, Ti, Nb and Ca as well is heated, is subjected to rough rolling, is thereafter subjected to finish rolling in which rolling finishing temperature is controlled to 780 to 980 deg.C, is next rapidly cooled to a first temperature within the range of 620 to 780 deg.C, is isothermally held to the same temperature for 1.0 to 10 sec or is slowly cooled from the same temperature to a second temperature within the range of less than the same temperature to >=600 deg.C at <=20 deg.C/s, is then cooled to a third temperature within the range of 300 to 500 deg.C at >=50 deg.C/s and is coiled, and the coiled coil is held in the temperature range of 300 to 500 deg.C in such a manner that the temperature changing rate is controlled to the range of -30 to 30 deg.C/h for 30 to 300 min and is thereafter air-cooled.
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