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Parts manufactured by pressing from iron-base powders possess a certain porosity. The pores form a system of communicating capillaries inside the part which absorb the ambient products (gases from the atmosphere, dissolved substances from solutions) under the action of the capillary forces and diffusion. This causes surface and internal corrosion of the material. In order to prevent oxidation of parts produced from powder materials in their transportation, storage, and operation their surface should be coated by a thin oxide film (as in blueing) in which the pores are closed by the oxides. The results of a study of the composition of oxide phases in sintered porous steels after a steam oxide treatment by two regimes are presented.In accordance with the existing concepts of the kinetics of iron oxidation the composition of the oxide phases depends on the oxidation temperature and the nature of the oxidizing agent. For example, at room temperature iron oxidizes to Fe_~O 3, which causes corrosion (Fe203 9 H20 ) in the presence of moisture. When iron is heated above 200~ it is coated by an oxide film of the F%O 4 type (magnetite). Oxides of this type exist up to t < 570~ At t > 570~ the FeO oxide (wiistite) becomes more stable. Both magnetite and wiistite form very fine films on the iron surface, which protect the part from further oxidation at conventional temperatures [1 ].

The possibilities of the use of power-saving processes of cyaniding and boronizing instead of the traditional gas nitriding without deterioration of the service stability of the tools are described. The nitriding process is shown to be intensified by treatment in a vibrofluidized bed.

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