FIELD: physics.
SUBSTANCE: invention relates to processing of molded articles with iron or steel surface with carbon content up to 2.06 wt. % before cold forming. In the method, the molded article is brought into contact with an aqueous acid composition to form a conversion layer as a separating layer. Aqueous acidic composition mainly consists of water, from 2 to 500 g/l of oxalic acid, calculated as anhydrous oxalic acid, and from 0.01 to 20 g/l of at least one guanidine based accelerator, calculated as nitroguanidine, and/or from 0.01 to 20 g/l of at least one nitrate, calculated as sodium nitrate. Loss of substance during etching with said aqueous acidic composition, measured by gravimetric determination, is in range of 1 to 6 g/m2, weight of dried conversion layer is in range from 1.5 to 15 g/m2, and ratio of loss of substance during etching (LE) and weight of layer (WL) of dried conversion layer (LE:WL) is in range (0.30–0.75):1.
EFFECT: dried conversion layer forms an adhesive-hard coating.
26 cl, 1 dwg, 7 tbl
