A steel sheet for heat treatment having a chemical composition comprising, by mass%: C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn: 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; and optionally one or more of: Cr: 0 to 1.0%; Ni: 0 to 2.0%; Cu: 0 to 1.0%; Mo: 0 to 1.0%; V: 0 to 1.0%; Ca: 0 to 0.01%; Al: 0 to 1.0%; Nb: 0 to 1.0%; REM: 0 to 0.1%; and the balance: Fe and impurities, wherein a maximum height roughness Rz on a surface of the steel sheet is 3.0 to 10.0 μm, the maximum height roughness Rz being specified in JIS B 0601 , and a number density of carbide being present in the steel sheet and each having circle-equivalent diameters of 0.1 μm or larger is 8.0 × 10 3 /mm 2 or lower, the number density of carbide having circle-equivalent diameters of 0.1 μm or larger being determined by: etching the surface of a steel sheet for heat treatment using a picral solution, magnifying 2000 times under a scanning electron microscope and observing in a plurality of visual fields, counting the number of visual fields where carbides having circle-equivalent diameters of 0.1 μm or larger are present and calculating a number per 1 mm 2 , and wherein a Mn segregation degree α expressed by a following formula (i) is 1.6 or lower: α = Maximum Mn concentration mass % at sheet-thickness center portion / Average Mn concentration mass % in 1⁄4 sheet-thickness depth position from surface the Maximum Mn concentration (mass%) at sheet-thickness center portion being determined by: subjecting the sheet-thickness center portion of a steel sheet to line analysis in a direction perpendicular to a thickness direction with an electron probe microanalyzer, selecting the three highest measured values from the results of the analysis, and calculating the average value of the measured values, the Average Mn concentration in a 1⁄4 sheet-thickness depth position from a surface being determined by: subjecting 10 spots in the 1⁄4 sheet-thickness depth position of a steel sheet to analysis in a direction perpendicular to a thickness direction with an electron probe micro analyzer, and calculating the average value thereof. C: 0.05 to 0.50%; Si: 0.50 to 5.0%; Mn: 1.5 to 4.0%; P: 0.05% or less; S: 0.05% or less; N: 0.01% or less; Ti: 0.01 to 0.10%; B: 0.0005 to 0.010%; Cr: 0 to 1.0%; Ni: 0 to 2.0%; Cu: 0 to 1.0%; Mo: 0 to 1.0%; V: 0 to 1.0%; Ca: 0 to 0.01%; Al: 0 to 1.0%; Nb: 0 to 1.0%; REM: 0 to 0.1%; and the balance: Fe and impurities, wherein etching the surface of a steel sheet for heat treatment using a picral solution, magnifying 2000 times under a scanning electron microscope and observing in a plurality of visual fields, counting the number of visual fields where carbides having circle-equivalent diameters of 0.1 μm or larger are present and calculating a number per 1 mm 2 , and wherein a Mn segregation degree α expressed by a following formula (i) is 1.6 or lower: α = Maximum Mn concentration mass % at sheet-thickness center portion / Average Mn concentration mass % in 1⁄4 sheet-thickness depth position from surface the Maximum Mn concentration (mass%) at sheet-thickness center portion being determined by: subjecting the sheet-thickness center portion of a steel sheet to line analysis in a direction perpendicular to a thickness direction with an electron probe microanalyzer, selecting the three highest measured values from the results of the analysis, and calculating the average value of the measured values, the Average Mn concentration in a 1⁄4 sheet-thickness depth position from a surface being determined by: subjecting 10 spots in the 1⁄4 sheet-thickness depth position of a steel sheet to analysis in a direction perpendicular to a thickness direction with an electron probe micro analyzer, and calculating the average value thereof. <EOS>