Abstract: A high carbon hot-rolled steel sheet which is a hot-rolled spheroidizing annealed material, including 0.2 to 0.7% C, 2% or less Si, 2% or less Mn, 0.03% or less P, 0.03% or less S, 0.08% or less Sol.Al., and 0.01% or less N, by mass, which contains carbide having a particle size of smaller than 0.5 ?m in a content of 15% or less by volume to the total amount of carbide, and the difference between the maximum hardness Hv max and the minimum hardness Hv min, ?Hv (=Hv max?Hv min), in the sheet thickness direction being 10 or smaller.

Abstract: A high carbon cold-rolled steel sheet having both excellent stretch-flange formability and excellent homogeneity of hardness in the sheet thickness direction is provided by a manufacturing method having the steps of: hot-rolling a steel containing 0.2 to 0.7% C by mass at finishing temperatures of (Ar3 transformation point ?20° C.) or above to prepare a hot-rolled sheet; cooling the hot-rolled sheet to temperatures of 650° C. or below at cooling rates from 60° C./s or larger to smaller than 120° C./s; coiling the hot-rolled sheet after cooling at coiling temperatures of 600° C. or below; cold-rolling the coiled hot-rolled sheet at rolling reductions of 30% or more to prepare a cold-rolled sheet; and annealing the cold-rolled sheet at annealing temperatures from 600° C. or larger to Ac1 transformation point or lower.

Abstract: A high carbon hot-rolled steel sheet which is a hot-rolled spheroidizing annealed material, including 0.2 to 0.7% C, 2% or less Si, 2% or less Mn, 0.03% or less P, 0.035 or less S, 0.08% or less Sol.Al., and 0.01% or less N, by mass, which contains carbide having a particle size of smaller than 0.5 ?m in a content of 15% or less by volume to the total amount of carbide, and the difference between the maximum hardness Hv max and the minimum hardness Hv min, ?Hv (=Hv max?Hv min), in the sheet thickness direction being 10 or smaller.

Abstract: A high carbon hot-rolled steel sheet, as a hot-rolled spheroidizing annealed material, having both excellent stretch-flange formability and excellent homogeneity of hardness in the sheet thickness direction is provided by a manufacturing method having the steps of: hot-rolling a steel containing 0.2 to 0.7% C by mass at finishing temperatures of (Ar3 transformation point?20° C.) or above to prepare a hot-rolled sheet; cooling the hot-rolled sheet to temperatures of 650° C. or below at cooling rates from 60° C./s or larger to smaller than 120° C./s; coiling the hot-rolled sheet after cooling at coiling temperatures of 600° C. or below; and annealing the coiled hot-rolled sheet at annealing temperatures from 640° C. or larger to Ac1 transformation point or lower.

Abstract: A high carbon cold-rolled steel sheet having both excellent stretch-flange formability and excellent homogeneity of hardness in the sheet thickness direction is provided by a manufacturing method having the steps of: hot-rolling a steel containing 0.2 to 0.7% C by mass at finishing temperatures of (Ar3 transformation point ?20° C.) or above to prepare a hot-rolled sheet; cooling the hot-rolled sheet to temperatures of 650° C. or below at cooling rates from 60° C./s or larger to smaller than 120° C./s; coiling the hot-rolled sheet after cooling at coiling temperatures of 600° C. or below; cold-rolling the coiled hot-rolled sheet at rolling reductions of 30% or more to prepare a cold-rolled sheet; and annealing the cold-rolled sheet at annealing temperatures from 600° C. or larger to Ac1 transformation point or lower.

Abstract: There is provided a cleaning apparatus for a surface of a sheet steel capable of satisfactorily removing scale from a surface of a sheet steel before, for example, hot rolling. Waters (42a, 46a) are ejected from nozzles (42, 46), with an ejection pressure of 100 kg/cm.sup.2, a flow rate of 60 liters/minute and an ejection angle of 20.degree. with respect to normal of the surface (32a) of the sheet steel, toward a downward-stream end with respect to a carrying direction. On the other hand, waters (44a, 48a) are ejected also from nozzles (44, 48), with the same ejection pressure, flow rate and ejection angle as those of the nozzles (42, 46), but different in the ejecting direction. That is, waters (44a, 48a) are ejected toward an upward-stream end with respect to the carrying direction.