High-strength hot rolled steel sheet and method for manufacturing the same

A method of manufacturing a high-strength hot rolled steel sheet with a yield strength of not less than 530 MPa by hot rolling a steel, wherein the steel has a chemical composition including, by mass %:

• C:
• more than 0.010% and not more than 0.06%,
• Si:
• not more than 0.3%,
• Mn:
• not more than 0.8%,
• P:
• not more than 0.03%,
• S:
• not more than 0.02%,
• Al:
• not more than 0.1%,
• N:
• not more than 0.01% and Ti:
• 0.05 to 0.10%,
• the balance comprising Fe and inevitable impurities, the method comprising:
• rough rolling the steel in an austenite single phase region,
• finish rolling the resultant steel sheet after rough rolling at a finishing delivery temperature of 860° C. to 1050° C.,
• cooling the steel sheet at an average cooling rate of not less than 30° C./s in a temperature range of from a temperature after the completion of the finish rolling to 750° C., and
• coiling the steel sheet into a coil at a coiling temperature of 580° C. to 700° C., wherein
• the steel sheet includes a metal microstructure in which a ferrite phase represents an area ratio of not less than 95%,
• ferrite crystal grains in the ferrite phase have an average crystal grain size of not less than 1 μm,
• the ferrite crystal grains contain TiC precipitate particles with an average particle size of not more than 7 nm dispersed in the ferrite crystal grains, and
• a ratio of the number of Ti atoms to the number of C atoms, Ti/C, in TiC is less than 1.