| 主权项 |
1. A method of manufacturing the hot-rolled steel sheet, the method comprising,
first hot rolling carried out at least once at a rolling reduction ratio of 20% or more in a temperature range of 1000° C. to 1200° C., and an austenite grain diameter is set to 200 μm or less, wherein an ingot or slab containing, by mass %: C: 0.0001% to 0.40%, Si: 0.001% to 2.5%, Mn: 0.001% to 4.0%, P: 0.001% to 0.15%, S: 0.0005% to 0.03%, Al: 0.001% to 2.0%, N: 0.0005% to 0.01%, O: 0.0005% to 0.01%, and further comprising one or two or more of: Ti: 0.001% to 0.20%, Nb: 0.001% to 0.20%, V: 0.001% to 1.0%, W: 0.001% to 1.0%, B: 0.0001% to 0.0050%, Mo: 0.001% to 1.0%, Cr: 0.001% to 2.0%, Cu: 0.001% to 2.0%, Ni: 0.001% to 2.0%, Co: 0.0001% to 1.0%, Sn: 0.0001% to 0.2%, Zr: 0.0001% to 0.2%, As: 0.0001% to 0.50%, Mg: 0.0001% to 0.010%, Ca: 0.0001% to 0.010%, and REM: 0.0001% to 0.1% and balance composed of iron and inevitable impurities; second hot rolling in which a total of rolling reduction ratios is 50% or more is carried out in a temperature range of T1+30° C. to T1+200° C.; third hot rolling in which a total of rolling reduction ratios is less than 30% is carried out in a temperature range of T1° C. to lower than T1+30° C.; and hot rolling ends at an Ar3 transformation temperature or higher, where, T1 is a temperature determined by steel sheet components, and expressed by the following formula 1,
T1(° C.)=850+10×(C+N)×Mn+350×Nb+250×Ti+40×B+10×Cr+100×Mo+100×V (Formula 1) |
