PURPOSE: To regenerate a rejected galvannealed steel sheet into a surface excellent in hot-dip galvanizing suitability again and to advantageously recycle it as a starting sheet for a hot-dip galvanized steel sheet for precoated galvanized steel sheet by subjecting the rejected galvannealed steel sheet to rolling first and then to the dissolution of plated layer by means of acid.
CONSTITUTION: Because the thickness of a rejected article, e.g., of galvannealed steel sheet, as rust-preventive surface treated steel sheet for automobile body use, or duplex galvannealed steel sheet, where Fe-rich plating is further applied to the galvannealed layer, rejected by surface defects is 0.65-0.9mm, this rejected article is rolled at ∞10% reduction of area first and then the galvannealed layer is dissolved by means of acid, such as sulfuric acid, and removed by ≥5%. On the other hand, nearly all hot-dip galvanized sheet sheets for precoated galvanized steel sheets have 0.15-0.5mm thickness, and, as a result, the rolled and acid-treated galvannealed steel sheet can be advatangeously recycles as a hot-dip galvanized steel sheet for precoated galvanized thin steel sheet.
I KANJI
KONISHI MOTOYUKI
IRIE TOSHIO
