An internal oxidation starting temperature, estimation device estimates an internal oxidation starting temperature which is a minimum temperature required for an internal oxide layer to grow on a surface of an easily oxidizable element-containing hot-rolled steel sheet including Si, Mn, or Al or any combination thereof. The internal oxidation starting temperature estimation device includes an internal, oxidation starting temperature estimation unit that estimates the internal oxidation starting temperature on the basis of concentrations of the Si, the Mn, and the Al included in the easily oxidizable element-containing hot-rolled steel sheet.

An internal oxidation starting temperature, estimation device estimates an internal oxidation starting temperature which is a minimum temperature required for an internal oxide layer to grow on a surface of an easily oxidizable element-containing hot-rolled steel sheet including Si, Mn, or Al or any combination thereof. The internal oxidation starting temperature estimation device includes an internal, oxidation starting temperature estimation unit that estimates the internal oxidation starting temperature on the basis of concentrations of the Si, the Mn, and the Al included in the easily oxidizable element-containing hot-rolled steel sheet.

A rolled metal sheet includes an obverse surface and a reverse surface that is a surface located opposite to the obverse surface. At least either one of the obverse surface and the reverse surface is a processing object. A method for manufacturing a metal mask substrate includes reducing a thickness of the rolled metal sheet to 10 μm or less by etching the processing object by 3 μm or more by use of an acidic etching liquid, and roughening the processing object so that the processing object becomes a resist formation surface that has a surface roughness Rz of 0.2 μm or more, thereby obtaining a metal mask sheet.

A rolled metal sheet includes an obverse surface and a reverse surface that is a surface located opposite to the obverse surface. At least either one of the obverse surface and the reverse surface is a processing object. A method for manufacturing a metal mask substrate includes reducing a thickness of the rolled metal sheet to 10 μm or less by etching the processing object by 3 μm or more by use of an acidic etching liquid, and roughening the processing object so that the processing object becomes a resist formation surface that has a surface roughness Rz of 0.2 μm or more, thereby obtaining a metal mask sheet.

A method of inspecting an elongated metal plate is provided, including measuring longitudinal direction metal plate thicknesses, measuring width direction metal plate thicknesses, and selecting the metal plate that satisfies condition (1), (B/A)×100 (%) is 5% or less, A being an average value of the longitudinal direction metal plate thicknesses, and B being obtained by multiplying a standard deviation of the longitudinal direction metal plate thicknesses by 3, and that satisfies condition (2), (C/X)×100 (%) is 3% or less, C being a value obtained by multiplying a standard deviation of the width direction metal plate thicknesses by 3, and X being a central portion width direction metal plate thickness obtained when the width direction metal plate thicknesses are measured to calculate the standard deviation of the metal plate thicknesses in the width direction.

A method of inspecting an elongated metal plate is provided, including measuring longitudinal direction metal plate thicknesses, measuring width direction metal plate thicknesses, and selecting the metal plate that satisfies condition (1), (B/A)×100 (%) is 5% or less, A being an average value of the longitudinal direction metal plate thicknesses, and B being obtained by multiplying a standard deviation of the longitudinal direction metal plate thicknesses by 3, and that satisfies condition (2), (C/X)×100 (%) is 3% or less, C being a value obtained by multiplying a standard deviation of the width direction metal plate thicknesses by 3, and X being a central portion width direction metal plate thickness obtained when the width direction metal plate thicknesses are measured to calculate the standard deviation of the metal plate thicknesses in the width direction.

An aspect of the present invention relates to a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.4≤0.4*Cr+Si≤3.2 (wherein element symbols denote measurements of respective element contents by weight %).

An aspect of the present invention relates to a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.4≤0.4*Cr+Si≤3.2 (wherein element symbols denote measurements of respective element contents by weight %).

A rolled metal sheet includes an obverse surface and a reverse surface that is a surface located opposite to the obverse surface. At least either one of the obverse surface and the reverse surface is a processing object. A method for manufacturing a metal mask substrate includes reducing a thickness of the rolled metal sheet to 10 μm or less by etching the processing object by 3 μm or more by use of an acidic etching liquid, and roughening the processing object so that the processing object becomes a resist formation surface that has a surface roughness Rz of 0.2 μm or more, thereby obtaining a metal mask sheet.

A rolled metal sheet includes an obverse surface and a reverse surface that is a surface located opposite to the obverse surface. At least either one of the obverse surface and the reverse surface is a processing object. A method for manufacturing a metal mask substrate includes reducing a thickness of the rolled metal sheet to 10 μm or less by etching the processing object by 3 μm or more by use of an acidic etching liquid, and roughening the processing object so that the processing object becomes a resist formation surface that has a surface roughness Rz of 0.2 μm or more, thereby obtaining a metal mask sheet.