SU1696578A1 - Method of thermal and chemical treatment of nickel band - Google Patents

Abstract

The invention relates to metallurgy, in particular to the chemical and heat treatment of metals and alloys, and can be used, in particular, to produce protective coatings on nickel conveyor belts for heat treatment of ferrites. The aim of the invention is to increase the operational durability, mechanical properties and corrosion resistance of nickel tape. The method includes diffusion chromium plating of nickel tape and additional annealing in air at 890 - 990 ° C for 5-90 minutes, followed by air cooling to room temperature. The proposed method provides an increase in the operational durability of nickel tape by increasing the quality of the coating, bending and stretching resistance when interacting with vapor and sulfur oxides under conditions of oxygen deficiency. 2 tab.

Description

The invention relates to metallurgy, in particular to the chemical and heat treatment of metals and alloys, and can be used, in particular, to produce protective coatings on nickel belts of conveyor electric furnaces for the thermal treatment of ferrites.

The aim of the invention is to increase the operational durability, mechanical properties and corrosion resistance of nickel tape.

The method includes diffusion chromium plating of nickel tape and subsequent annealing in air at 890–990 ° C for 5–90 min, followed by air cooling to room temperature.

The proposed additional annealing provides a dense film of chromium oxides on the surface of the nickel tape, which significantly slows down the diffusion of vapor and sulfur oxides to the core of the tape in conditions of oxygen deficiency. The amount of nickel sulphurous compounds is reduced, which does not preserve much of the ductility in an environment of vapors and sulfur oxides.

Without such an annealing, the chrome-plated layer has a porous structure, as a result of which thermal treatment of ferrites under conditions of oxygen deficiency results in fragile nickel sulphurous compounds, which lead to peeling of the coating and a decrease in the bending resistance of the tape.

Conduct additional annealing at 890-990 ° C. within 5-90 minutes, it improves the quality of the coating and the durability of the tape to bend when it interacts with vapor and sulfur oxides under conditions of oxygen deficiency, which leads to an increase in the service life of the tape.

Going beyond these modes leads either to nickel diffusion to the surface, or to the formation of an insufficiently dense oxide film. In both cases, a series of AOs is formed.

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Solid nickel compounds and tape density are reduced.

Example. Pre-defatted nickel tape with a thickness of 0.3 mm is subjected to chrome plating in a mixture of composition, wt.%: Cr 50; A120Z 49; NH4C 1 at 1000 ° C for b h in a container of heat-resistant steel with a fusible bolt. Pallets of 75 x 85 x 5 mm are made of this tape and are annealed in a chamber furnace in the temperature range of 850-1100 ° C with exposures of 5-120 min and then cooled in air to room temperature. In the pallets prepared by the proposed method, the thermal decomposition of a mixture of sulphate salts of iron, nickel, zinc, manganese and medm, used to obtain ferrites, at 960 ° C for 20 minutes is repeatedly carried out. After 40 minutes of using the pallets, samples are cut out in the form of 80 x 15 mm stripes, which are subjected to a bending test.

For comparison, two pallets are not annealed, and one pallet is made from a tape without diffusion chrome plating. After their work in the environment of vapor and sulfur oxides, the same samples are cut out of these pallets. The quality of the coating and the durability of the belts are estimated by the number of pereg-. Bov samples before destruction (bending radius 2 mm, bending angle 90 °).

The test results are summarized in table. one.

As follows from the table. 1, a sample of uncoated nickel tape (No. 1) after 240 minutes of work in an environment of vapor and sulfur oxides is destroyed after a single bend.

Diffusion chrome plating without additional annealing (Samples No. 2 and No. 3) does not give an increase in the service life of the tapes as compared with the uncoated nickel tape {Sample No. 1). When the ribbon samples are operated in vapor and sulfur oxides, the coating peels off after 60 minutes (sample no. 3). I Diffusion chromium plating with additional annealing gives a significant increase in the durability of the coating and an increase in the service life of the tape. The best results were obtained on samples N 4 - 9, which were annealed in the temperature range of 890 - 990 ° С and shutter speeds of 5-90 min.

At temperatures below 890 ° C, even with exposures of 120 minutes, the quality of the coating is much worse, since a protective film of chromium oxides does not have time to form in the tape coating (sample No. 10). At temperatures above 990 ° C, even with a shutter speed of 3 minutes, the coating exfoliates, causing, during operation in an environment of vapor and sulfur oxides, to form

brittle nickel compounds, which reduces the service life of nickel tapes (sample No. 12). The same phenomena also occur at lower temperatures (940 ° C) at exposures of more than 90 min (sample No. 11).

Samples of nickel tape are also subjected to tensile and corrosion resistance tests. For this purpose, according to GOST, samples of appropriate sizes are made, which after annealing and thermal decomposition of the mixture on them (as before bending tests) are subjected to tests for corrosion resistance by a gravimetric method and for stretching on an INSTRON tensile testing machine. The quality of the coating and the service life of the nickel tape are estimated from the values of the temporary tensile strength of the stj, relative to the elongation and weight gain per unit area of such samples. For comparison, one sample without annealing and one sample without diffusion chrome plating are subjected to tests.

The test results are given in

tab. 2

As follows from the table. 2, a sample of uncoated nickel tape (No. 1) after 240 minutes of work in an environment of vapors and sulfur oxides has a low temporary tensile strength and high elongation. This leads to a rapid sagging followed by the destruction of a conveyor belt of such a material that works in flexure.

Diffusion chrome plating without additional annealing (sample 2) reduces the temporary tensile strength and relative elongation due to the formation of fragile nickel sulfur compounds.

A low value of temporary tensile strength leads to a rapid destruction of the conveyor belt of such material.

Diffusion chromium plating with additional annealing gives a significant increase in the temporary resistance to rupture (and, consequently, the service life of nickel tape) and a slight increase in the relative elongation as compared with sample No. 2 without additional annealing,

although this value remains lower than sample No. 1 without coating. However, since the tension of the conveyor belt can be adjusted, small fluctuations (within 1–10%) of the relative elongation significantly

on the service life of the tape is not affected.

The best results in strength properties were obtained on samples No. 3, 6, 7 (Table 2), which were annealed in the temperature range of 890 - 990 ° С and shutter speeds of 5-90 min.

At annealing temperatures below 890 ° C, even with exposures of 120 min, the quality of the coating is worse, since it does not have time to pass the diffusion of chromium and form a dense film of oxides with a uniform chromium content. At temperatures above 990 ° C, even at a shutter speed of 3 minutes, nickel diffuses to the surface, resulting in brittle nickel compounds during operation in the environment of sulfur vapors and sulfur oxides, which reduces the amount of temporary resistance to rupture, and hence the duration nickel tape service (sample number 5, Table 2). The same phenomena also occur at lower temperatures (940 ° C) and exposures of more than 90 minutes (Sample No. 8, Table 2).

The corrosion resistance of all samples is the same within the measurement error. The relatively high weight gain per unit area is explained by the presence of residual ferrite mixture on the samples.

Thus, the results of bending, tensile, and corrosion resistance tests show that using the proposed method provides an increase in

the operational durability of the tape by improving the quality of the coating, the durability of the tape on bending and stretching (without deteriorating the corrosion resistance) when interacting with vapor and sulfur oxides in

oxygen deficiency conditions.

Claims (1)

Invention Formula The method of chemical-thermal treatment of nickel tape, including diffusion chrome plating, characterized in that, in order to increase the service durability of the tape, mechanical properties and corrosion resistance of the products, after diffusion chromium plating, annealing is carried out in air at 890-990 ° C for 5 -90 min followed by air cooling to room temperature. Table 1 Table 2