High-strength hot-rolled steel sheet and method for producing same

A high-strength hot-rolled steel sheet comprising a chemical composition containing, in mass %,

• C:
• 0.06% or more and 0.1% or less,
• Si:
• 0.09% or less,
• Mn:
• 0.7% or more and 1.3% or less,
• P:
• 0.03% or less,
• S:
• 0.01% or less,
• Al:
• 0.1% or less,
• N:
• 0.01% or less,
• Ti:
• 0.14% or more and 0.20% or less,
• V:
• 0.07% or more and 0.14% or less, and
• the balance being Fe and incidental impurities,
• wherein the steel sheet has microstructures such that an area ratio of ferrite phase is 95% or more, an average grain size of the ferrite phase is 8 μm or less, and carbides in grains of the ferrite phase have an average particle size of less than 10 nm, and
• wherein the steel sheet has a tensile strength of 980 MPa or more.

A method of producing a high-strength hot-rolled steel sheet, comprising:

• heating a steel material;
• subjecting the steel material to hot rolling including rough rolling and finish rolling;
• and
• after completion of the finish rolling, cooling and coiling thus rolled steel material to gain a hot-rolled steel sheet,
• wherein the steel material has a chemical composition containing, in mass %,
• C:
• 0.06% or more and 0.1% or less,
• Si:
• 0.09% or less,
• Mn:
• 0.7% or more and 1.3% or less,
• P:
• 0.03% or less,
• S:
• 0.01% or less,
• Al:
• 0.1% or less,
• N:
• 0.01% or less,
• Ti:
• 0.14% or more and 0.20% or less,
• V:
• 0.07% or more and 0.14% or less, and
• the balance being Fe and incidental impurities, and
• wherein the steel material is heated at a temperature of 1100° C. or higher and 1350° C. or lower, the finish rolling is operated at a finish rolling temperature of 850° C. or higher, the cooling is initiated within 3 seconds after completion of the finish rolling, the cooling is operated at an average cooling rate of 20° C./s or higher, and the coiling is operated at a coiling temperature of 550° C. or higher and 700° C. or lower.