STUDY OF LAYER COMPOSITION DURING NITRIDING AND STEAM OXIDATION OF COMPOSITE STEELS.

Аннотация

The article examines the structural and phase changes in surface diffusion nitride-oxide coatings obtained during nitriding in a gas environment followed by oxidation of ferrite-pearlite steels in water vapor, as well as the influence of phase changes on the corrosion properties. Key words: ferrite, pearlite, nitriding, oxidation, diffusion coating, nitride layer, corrosion resistance. Introduction. When the nitride layer is oxidized in the vapor of oxyethylidene biphonic acid solution by nitriding at a high nitrogen potential, in addition to iron, in the presence of carbon in the steel matrix, a high nitrogen nitride layer ε -phase (Fe N) can be obtained. As a result, the carbonitride εʹ 2−3 phase (Fe (NC)) is formed, and at the next stage, due to the dissociation of 2−3 high nitrogen nitride by oxidation, creating a barrier oxide layer, the nitrogen layer carbonitride -phase (Fe (NC, oxycarbonitride) consists of a mixture of 2−3 εʹʹ-phase (Fe (NSO)), -phase (Fе N) (Fig. 1 ). 2−3 4 Methods. As the duration of oxidation increases, the thickness of the oxide layer due to the release of dispersed nitride particles in the inner nitride zone and dissociation with the nitride zone leads to a mixture of --, -phases and - decrease in the thickness of the nitride layer (Fig. 1). Figure 1. Diffractogram of the nitride-oxide coating surface 155 ACADEMIC RESEARCH IN MODERN SCIENCE International scientific-online conference Nitriding and oxidation of Stal 45 at 5800С for 3 hours, and nitriding and oxidation at 5500С for 2.5 hours. FеКα radiation. The desired structure and composition of the phase composition of the nitride phases in the nitride-oxide coating can be achieved by changing individual technological conditions at each stage of the nitro-oxidation process. Results and its discussion Dissociation of the -phase takes place through the partial separation of the -phase and the formation of a low-nitrogen -phase at the expense of carbon from the matrix, as well as the formation of the -phase at the expense of carbon and saturated atmospheric oxygen. Picture. 2. Changes in the intensity of the ε(101), εʹ+γʹ (101), γʹ(200) and Fе О (110) lines of the nitride layer depending on the duration of 3 4 oxidation. Nitriding of steel 45 at a temperature of 5800С for 3 hours and oxidation at a temperature of 5500С. FеКα radiation. By forming a barrier oxide film on the surface, it is possible to ensure interdiffusion of nitrogen in the nitride layer, which allows changing the concentration of nitrogen between the phases, thereby achieving the desired composition and structure of the composition of the nitride phases. The nitrided part of the nitride-oxide coating can obtain an oxide layer with the desired composition of Fе O , which is responsible for the formation of anti- 3 4 corrosion oxide coatings on the surface of metal objects. 156 ACADEMIC RESEARCH IN MODERN SCIENCE International scientific-online conference As a result, the ε -phase is present in the concentration range of 4.55-11% with the γʹ-phase, and undergoes dissociation of nitrides during isothermal exposure. [1]. Currently, there is very little information about the effect of the quantitative ratio of ε- and γʹ-nitrides on the physico-chemical and physico-mechanical properties of the joint zone. At the same time, for the layers of compounds with a large proportion of the γʹ-phase, it is possible to determine a higher corrosion resistance than the layers with a higher proportion of ε-nitrides in the composite nitride-oxide coating [2]. In the first stage of nitrification, nitrogen dissociation rate (nitrogen potential) during nitrogen oxidation at a temperature of 〖5800С according to the regime of two-stage change: α =30-45% in 1 hour and α =45-60% in 2 hours (total duration 3 hours) and in the second step, after oxidation at 5500C for 1 hour, a nitride layer is obtained, which is as follows: - ε -phase, ε+γʹ -phase, γʹ-phase, as well as the surface layer of Fе О oxide 3 4 (Fig. 2). [3]. A wide range of individual nitride phases lies between the saturation temperature and the eutectoid temperature of nitridation. By changing the degree of dissociation of ammonia on the surface of the treated part, it is possible to achieve the formation of high-nitrogen ε -phase, γʹ-phase and supersaturated or low-nitrogen α-solid solution. In particular, stable nitrides consisting of separate phases are formed at wide dissociation levels in the temperature range of 560-5800С. [4]. Figure 3. Diffractogram of the nitride-oxide coating surface 157 ACADEMIC RESEARCH IN MODERN SCIENCE International scientific-online conference Nitriding at a temperature of 5800С in a two-step change in the degree of dissociation of Stal 45: 2 hours at α =30-45% and 1 hour at α =45-60% (3 hours in total) and 1 hour at 5500С oxidation. It is cooled in a vessel to 4000С, and then in oil. FеКα radiation. Regulating the phase composition of the nitrided layer is also achieved by c