Hot-rolled steel sheet and manufacturing method thereof

A manufacturing method of a hot-rolled steel sheet, comprising:

• smelting a steel having a composition containing:
• in mass %,
• C:
• 0.01 to 0.2%;
• Si:
• 2.5% or less (not including “0” (zero));
• Mn:
• 4.0% or less (not including “0” (zero));
• P:
• 0.10% or less;
• S:
• 0.03% or less;
• Al:
• 0.001 to 2.0%;
• N:
• 0.01% or less (not including “0” (zero));
• O:
• 0.01% or less (not including “0” (zero));
• Ti:
• 0.03 to 0.30%;
• Nb:
• “0” (zero) to 0.30%;
• Cu:
• “0” (zero) to 2.0%;
• Ni:
• “0” (zero) to 2.0%;
• Mo:
• “0” (zero) to 1.0%;
• V:
• “0” (zero) to 0.3%;
• Cr:
• “0” (zero) to 2.0%;
• Mg:
• “0” (zero) to 0.01%;
• Ca:
• “0” (zero) to 0.01%;
• REM:
• “0” (zero) to 0.1%;
• B:
• “0” (zero) to 0.01%;
• and
• the balance being composed of iron and impurities and casting the steel into a slab, and then directly heating the cast slab to 1200° C. or higher or once cooling the cast slab and then heating the cast slab to 1200° C. or higher;
• performing hot rolling in which a reduction ratio of rolling at the final stage of rough rolling is set to 25% or more and a rolling temperature is set to lower than 1100° C. and the rough rolling is completed, an obtained rough-rolled piece is heated by 10° C. or higher before finish rolling, and a finishing temperature of finish rolling to be performed subsequently is set to 900° C. or higher;
• and
• performing cooling at an average cooling rate of 50° C./sec or more from the finishing temperature of the finish rolling to 400° C. and performing coiling at 100° C. or higher to lower than 400° C.