HIGH-STRENGTH HOT-ROLLED STEEL PLATE AND MANUFACTURING METHOD THEREFOR

摘要

On a cross section with a sheet width direction of a high-strength hot-rolled steel sheet set as a normal line, with regard to an inclusion having a major diameter of 3.0 µm or more, a maximum of a major diameter/minor diameter ratio expressed by (a major diameter of the inclusion)/(a minor diameter of the inclusion) is 8.0 or less, and a sum total of a rolling direction length per 1 mm 2 cross section of a predetermined inclusion group composed of plural inclusions each having a major diameter of 3.0 µm or more and a predetermined extended inclusion having a length in a rolling direction of 30 µm or more is 0.25 mm or less. The plural inclusions composing the predetermined inclusion group congregate in both the rolling direction and a direction perpendicular to the rolling direction 50 µm or less apart from each other. The predetermined extended inclusion is spaced over 50 µm apart from all the inclusions each having a major diameter of 3.0 µm or more in at least either the rolling direction or the direction perpendicular to the rolling direction.