Abstract: In an H-section steel, which has a predetermined chemical composition, a thickness of the flange is from 25 to 140 mm; an average crystal grain diameter is 38 ?m or less and the area fraction of a martensite-austenite constituent is 1.2% or less, in a plane orthogonal to the width direction of the flange, centering on a measurement position 7 that is a position separated, in the width direction of the flange, from the end face in the width direction of the flange by (?)F, and separated, in the thickness direction of the flange, from the outer face in the thickness direction of the flange by (¼)t2, when the width direction length of the flange is F and the thickness of the flange is t2; a yield strength or 0.

Abstract: In an H-section steel, which has a predetermined chemical composition, a thickness of the flange is from 25 to 140 mm; an average crystal grain diameter is 38 ?m or less and the area fraction of a martensite-austenite constituent is 1.2% or less, in a plane orthogonal to the width direction of the flange, centering on a measurement position 7 that is a position separated, in the width direction of the flange, from the end face in the width direction of the flange by (?)F, and separated, in the thickness direction of the flange, from the outer face in the thickness direction of the flange by (¼)t2, when the width direction length of the flange is F and the thickness of the flange is t2; a yield strength or 0.

Abstract: A device to cool a steel material having undergone hot rolling mills, the device including: a conveying mechanism which conveys the steel material while accelerating the steel material; a water cooling mechanism which cools the steel material while the conveying mechanism conveys the steel material; and a control unit which controls the conveying mechanism and the water cooling mechanism to cause the cooling of the steel material to satisfy Formula (1) below, wherein a water cooling time decrease rate ? in Formula (1) below is decided based on a length of a water cooling zone where the water cooling mechanism is provided and a time ?tc(0) required to cool a leading end portion of the steel material down to a target temperature, ?tc(x)=?tc(0)??·x??Formula (1), where x: a conveyance-direction position in the steel material relative to the leading end portion of the steel material serving as a reference point, and ?tc(x): a time required to cool a portion at the position x of the steel material down to the ta