HIGH-STRENGTH HOT-ROLLED STEEL SHEET AND MANUFACTURING METHOD THEREFOR, AND HIGH-STRENGTH ELECTRIC RESISTANCE WELDED STEEL PIPE AND MANUFACTURING METHOD THEREFOR

Provided are a high-strength hot rolled steel sheet and a method for producing the steel sheet, and a high-strength electric resistance welded steel pipe and a method for producing the steel pipe. In the steel microstructure of the high-strength hot rolled steel sheet according to the present invention at the thickness center of the steel sheet, the volume fractions of bainite and ferrite are specific values, the average grain size is 9.0 pm or less, and the dislocation density is 1.0 × 1014 m-2 or more and 1.0 × 1015 m-2 or less. In the steel microstructure of the steel sheet at a position 0.1 mm below the surface of the steel sheet, the volume fractions of bainite and ferrite are specific values, the average grain size is 9.0 pm or less, the dislocation density is 5.0 × 1014 m-2 or more and 1.0 × 1015 m-2 or less, and the maximum low angle grain boundary density is 1.4 × 106 m-1 or less. The thickness of the steel sheet is 15 mm or more.