Increasing the tribological properties of the sur-face layer of cast iron by treatment in the envi-ronment of overheated steam of aqueous solution

Abstract

The formation of the surface layer of cast iron during the processing of cast iron in the environment of superheated steam of an aqueous solution of salts is considered. An ecologically cleaner method of chemical-thermal treatment is offered. The article considers the surface layer obtained in the environment of superheated steam of an aqueous solution of water-soluble salts of ammonium molybdic acid. The layer is formed on the surface of the matrix and around the graphite inclusions. The impact of temperature on the formation of a multilayer coating by increasing the temperature in contact with the metal surface is the dissociation of chemical compounds in solution, with the formation of atomic oxygen, sulfur, nitrogen, molybdenum. The formation of the surface layer occurred not only on a metal base, but also on the boundaries of graphite, both lamellar and globular, coming to the surface of the metal without breaking the solid layer. It is established that as a result of interaction of technological parameters of temperature, holding time and concentration of saturated medium graphite in the surface layer changes its shape, becoming spherical, although in the matrix it had a lamellar shape. It is multiphase and contains soft and hard structural components. Comparative studies have shown that the wear rate of untreated cast iron is much higher than that of treated cast iron, and reaches 0.8 ∙ 10-4 μm/km at a load of 400 N. This increases the wear resistance of cast iron and at the same time improves the workability reducing the coefficient of friction. The effect of the coating on the workability show that the stabilization of the friction moment occurs faster in samples with a multilayer coating. Thus, for gray cast iron with lamellar graphite, the stabilization time of the friction moment in a multilayer coating is 0.6 h compared with 2 h for a single layer coating; in high-strength cast iron it is, respectively, 5.2 and 6.3 hours.