PURPOSE: To enable the production of a high tensile strength thin steel sheet having excellent press-formability by forming a specific roughness on the steel sheet surface and sticking a specific quantity of oil having a specific viscosity on the surface or forming a specific thickness of solid lubricating film of resin or wax.
CONSTITUTION: The oil having ≥50cst (40°C) viscosity at ≥1g/m2 or the solid lubricating film of resin or wax at ≥1μm thickness is applied on the surface of the steel sheet having Ra ≤0.4μm center line average roughness or Rz ≤4μm ten point average roughness at least in the one side surface of the steel sheet surface. When the roughness of the steel sheet surface does not satisfy the condition, the oil film is broken and the lubricity is deteriorated. When the lubricating film does not satisfy the condition, the oil film is broken and the lubricity is deteriorated. Therefore, the press-formability of the steel sheet is drastically improve the controlling the condition of the lubrication and the surface roughness of the high tensile strength thin steel sheet.
MIURA KAZUYA
HIRA TAKAAKI
IMANAKA MAKOTO
KATO TOSHIYUKI
