Hot-rolled steel sheet, cold-rolled steel sheet, galvanized steel sheet, and methods of manufacturing the same

摘要

A hot-rolled steel sheet has an average value of the X-ray random intensity ratio of a {100} <011> to {223} <110> orientation group at least in a sheet thickness central portion that is in a sheet thickness range of ⅝ to ⅜ from a steel sheet surface of 1.0 to 6.0, an X-ray random intensity ratio of a {332} <113> crystal orientation of 1.0 to 5.0, rC which is an r value in a direction perpendicular to a rolling direction of 0.70 to 1.10, and r30 which is an r value in a direction that forms an angle of 30° with respect to the rolling direction of 0.70 to 1.10.

主权项

1. A method of manufacturing a 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 a 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), wherein an average value of an X-ray random intensity ratio of a {100} <011> to {223} <110> orientation group at least in a sheet thickness central portion that is in a sheet thickness range of ⅝ to ⅜ from a steel sheet surface is 1.0 to 6.0 in the hot-rolled steel sheet, an X-ray random intensity ratio of a {332} <113> crystal orientation is 1.0 to 5.0 in the hot-rolled steel sheet; and rC which is an r value in a direction perpendicular to a rolling direction is 0.70 to 1.10, and r30 which is an r value in a direction that forms an angle of 30° with respect to the rolling direction is 0.70 to 1.10 in the hot-rolled steel sheet.