PURPOSE: To obtain a one-side hot dipped steel sheet with superior suitability to phosphating and superior corrosion resistance after coating by spraying insoluble phosphate of a metal on a one-side hot dipped steel sheet after removing an oxide film on the undipped side in a process of cooling the sheet.
CONSTITUTION: In a process of cooling a one-side hot dipped steel sheet, an oxide film formed on the undipped side is removed. A suspension of insoluble phosphate of a di- or trivalent metal such as Zn3(PO4)2, Ca2(PO4)2 or Fe(PO4) is then sprayed on the surface-activated one-side hot dipped steel sheet cooled to a low temp. By this treatment, fine phosphate crystals with superior coating performance are formed on the surface of the sheet. In addition, the corrosion resistance after coating is enhanced without deteriorating the solderability.
TANO KAZUHIRO
KAMATA MINORU
OKAMOTO SUSUMU
