| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for forming a lubricating film suitable for cold heading at high productivity without generating sludge. SOLUTION: By using an electrolytic soln. contg. 20 to 50 g/L zinc ions, 20 to 70 g/L phosphoric acid ions and 30 to 80 g/L nitric acid ions, electrolysis is executed at the current density of 20 to 100 A/dm2 with a metallic material for cold heading subjected to pickling or mechanical descaling and pickling as a cathode to form a chemical conversion film of phosphate of 6 to 20 g/m2, which is thereafter brought into contact with a water base or oil base lubricant. The electrolytic soln. preferably contains one or more among nitrous acid ions, hydrogen peroxide and chlorine ions and preferably contains one or more among Mg, Al, Ca, Cr, Fe, Ni and Cu. A molar ratio of the metallic ions to the phosphoric acid ions is preferably controlled to 0.3 to 2, and the molar ratio of the nitric acid ions to the phosphoric acid ions is preferably controlled to 0.1 to 3. |
