APPLICATION METHOD OF THERMAL DIFFUSION ZINC COATING, AND COUPLING WITH THERMAL DIFFUSION ZINC COATING

摘要

FIELD: metallurgy.;SUBSTANCE: chemical and heat treatment is performed at the temperature of 380-420°C in a rotating vessel in a suspended layer of modified zinc powder, which has a surface film of active zinc oxide. Content in the powder of a fraction with the powder size of less than 40 mcm is 10-40%. Treatment is started from loading of products into the vessel with powder heated up to the temperature of 330-360°C and ended with a stage of vacuum cooling to the temperature of 320-360°C during at least 50 minutes. Residual pressure at the cooling stage is maintained in the range of 0.1-0.3 kgf/sq.cm. Weight ratio of steel products to the modified powder is maintained on the level of 1.5 to 4.0. A steel coupling with a threaded surface has a thermal diffusion zinc coating with thickness of 31-60 mcm, which has a deviation from an average value of thickness on the threaded surface of not more than 20% and which has been applied by means of the above method. The coating has the ratio of G-phase thickness to δ-phase thickness in the range of 0.4 to 1.0; with that, δ-phase has a homogeneous structure and includes G-phase inclusions in the range of 5-10% by weight. Size of G-phase inclusions in δ-phase layer is 0.05 to 0.2 mcm.;EFFECT: on products with a threaded surface there obtained is a coating with improved operating properties, and namely with the number of screwing-unscrewing cycles at operation of more than 70 owing to improving ductility and wear resistance properties of the coating.;5 cl, 1 tbl, 5 ex