Chemical heat treamaent of machine parts and tools in gas media at 500 -600~ is widely used in the industry. However, the obvious advantages of the method are accompanied by certain serious disadvantages that reduce the range of its application. The present work is an attempt to realize a new approach to gas nitriding, solve some problems of the process, and widen the field of its application.During the 70 years of industrial use of the methods of low-temperature chemical heat treatment (CHT), various processes have been developed [1,2]. The use of these processes provides a high complex of operating properties of the processed parts, i.e., a high hardness, wear resistance, antiscore properties, heat, corrosion, and fatigue resistances. After a low-temperature CHT the geometrical sizes of the parts change very little because their saturation occurs at 500-600~ and is not accompanied by phase transformations of a martensite type. The possibility of obtaining a unique set of properties has stimulated a continuous development of the method [3]. However, the obvious merits of low-temperature nitrogen saturation of steels and alloys are accompanied by some substantial disadvantages. For example, classical gas nitriding, which is the main method of low-temperature CHT, lasts for a long time (as much as 90 h), causes a considerable decrease in the ductility of the hardened parts and a high brittleness of the surface layers, often cannot provide strengthened layers deeper than 0.6 mm, and is characterized by an unsatisfactory reliability of the processes, a low stability of the results under actual industrial conditions, and cannot be applied to some kinds of alloy the demand for which is growing steadily, nanaely, alloyed structural, tool and corrosion-resistant steels, composite materials, titanium-alloyed steels, and parts fabricated by the methods of powder metallurgy [4].Thus, the expediency of working on the elimination of these defects is obvious. Primarily this concerns gas nitriding and carbonitriding performed with the use of various saturating atmospheres in high-efficiency shaft, chamber, and through furnaces. Analyzing the published data on low-temperature CHT, we will see that the problems of gas nitriding should be solved by a basically new approach.A hypothesis suggested in this connection consists in changing the mechanism of the formation of the diffusion NllTavtoprom JSC, Moscow; Institute of Chemical Physics of the Russian Academy of Sciences, Chemogolovka, Moscow Region, Russia. layer on iron and alloys. Then the stable equilibrium products of the interaction of the components of the furnace atmosphere (in the most typical case these are products of the dissociation of ammonia) used as a nitriding medium should be replaced by intermediate labile chemically active formations such as nitrogen-, hydrogen-, and oxygen-containing radicals, ions, and ion radicals [5]. These nonequilibrium but sufficiently long-living "debris" which possess a high activity can change the mechanism of gas nitriding of metals...
