| 摘要 |
PURPOSE:To form high quality phosphate films on parts to be phosphated with a specified phosphating soln. by adding a material for lowering the oxidation- reduction potential of the soln. to the soln. in case where the potential rises over a prescribed range so as to keep the potential in the prescribed range. CONSTITUTION:A steel material is brought into contact with a phosphating soln. of 2.0-4.0 pH having 300-700mV oxidation-reduction potential normal hydrogen electrode potential) at 0-40 deg.C to form a phosphate film on the surface. The phosphating soln. contains phosphoric acid ions, ions of an oxoacid such as nitric acid, ions of a phosphate forming metal such as zinc and an oxidizing agent. In case where the oxidation-reduction potential of the phosphating soln. rises over the prescribed range of 300-700mV during the operation, an aq. soln. contg. bivalent iron ions such as an aq. FeSO4 soln. having about 0.1-1.0% concn. is added to lower the potential and to keep it in the prescribed range. Thus, a high quality phosphate film is formed on the surface of the steel material.
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