Abstract: In a cast-iron disc brake rotor (1), each of an outer sliding surface (2a) and an inner sliding surface (3a) is covered with a phosphate coating (8) by electrolysis of a phosphate coating solution containing therein phosphate ions, zinc ions and nitrate ions. This makes it possible to attain dramatically improved rust preventive performance for the sliding surfaces (2a) and (3a). The phosphate coating (8) has a thickness of 1 to 10 &mgr;m, a mass of 4 to 35 g/m2 and a grain size of less than 50 &mgr;m. Preferably, the thickness of the phosphate coating (8) is adjusted to 2 to 8 &mgr;m.

Abstract: In a cast-iron disc brake rotor (1), each of an outer sliding surface (2a) and an inner sliding surface (3a) is covered with a phosphate coating (8) by electrolysis of a phosphate coating solution containing therein phosphate ions, zinc ions and nitrate ions. This makes it possible to attain dramatically improved rust preventive performance for the sliding surfaces (2a) and (3a). The phosphate coating (8) has a thickness of 1 to 10 &mgr;m, a mass of 4 to 35 g/m2 and a grain size of less than 50 &mgr;m. Preferably, the thickness of the phosphate coating (8) is adjusted to 2 to 8 &mgr;m.

Abstract: Waterborne lubricants comprising: (A) water-soluble inorganic salt; (B) homogeneously dispersed solid lubricant; (C) at least one homogeneously emulsified substance selected from mineral oils, animal and plant oils and fats, and synthetic oils; (D) surfactant; and (E) water, in which the weight ratio (B)/(A) is from 0.05:1 to 2:1 and the weight ratio {C/(A+B)} is from 0.05:1 to 1:1, provide a one-step, highly lubricating waterborne lubricant for use in the cold plastic working of metals. This waterborne lubricant can replace the conversion coating treatment (phosphate, oxalate, etc.)+reactive soap treatment combined lubrication system now in general use and is free of the environmental issues associated with the combined lubrication system, provides for facile coating removal, and is not subject to the decline in seizure resistance caused by nonuniform add-on when large numbers of workpieces are treated together by immersion.