RU2791345C1 - Method for vanadizing surface layers of carbon steel - Google Patents

Abstract

FIELD: carbon steel substrate vanadizing.

SUBSTANCE: invention relates to a method for vanadizing the surface of a carbon steel substrate. A vanadium-containing coating containing 50 wt.% ammonium salt of 2-monoethanolamine and citric acid, 25 wt.% carbon black T-900 and 25 wt.% vanadium oxide V2O5 is applied. Then heating is carried out at a temperature of 950-1325°C with an exposure of 4.5-9.5 minutes.

EFFECT: improved quality of the coating due to the formation of a diffusion zone at the interface between the coating and the substrate and the productivity of the coating formation process.

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Description

The invention relates to a method of chemical-thermal treatment and can be used to improve the service life of carbon steel products.

A known method of surface hardening of metal products in a container filled with coal powder. The product is heated by passing an electric current using a container and a metal product as electrodes, while before placing the metal product in the container, a layer of liquid or gel-like electrically conductive adhesive material is applied to the surface of the product, and then a layer of powder of a material containing an alloying element, or a mixture of these components, as an adhesive material, a material is used that, when heated, does not emit products that prevent the diffusion of alloying elements into the surface of the product, for example, the Uniagel universal electrode gel manufactured by Geltek-Medica LLC for electrophysiological medical research of a composition based on glycerol, potassium chloride , propylene glycol, preservatives, water, thickener-carbomer polyacrylic acid. The method was experimentally tested on chromium plating (formation of (Cr,Fe) ₂₃ С ₆ and (Cr,Fe) ₇ С ₃ ), borating (formation of Fe ₂ B), molybdenation (formation of Mo ₂ C), nitriding and carbonitriding (formation of Fe ₃ N, Fe ₄ N, CrN and Fe ₃ (N, C)), while increasing the microhardness of steel products (Diffusion carbide coatings / VF Loskutov et al.-K.: Tekhnika, 1991, p. 54). It is possible that vanadization of steel can be carried out in this way.

Thus, the proposed method makes it possible to harden the surface of a metal product by forming a highly hard alloyed layer.

A known method of simultaneous vanadization and boriding using coating applied to the surface of a steel sample based on an electrically conductive gel containing powders of ferrovanadium FeV80 and boron carbide B ₄ C (Stepanov M.S. Structure, phase composition, mechanical properties, wear resistance of steel after microarc boron vanadization / M S. Stepanov, Y. M. Dombrovsky, L. V. Davidyan // Proceedings of higher educational institutions. Ferrous metallurgy.-2019. V. 62. No. 6. P. 446-451-prototype). A surface layer 150–190 µm thick is formed on the steel, having a base with a microhardness of 7.8–8.3 GPa, in which light gray granular inclusions and eutectic regions with a microhardness of 13.5–14.0 GPa are located. Next, there is a carburized layer of eutectoid concentration, which passes into the original ferrite-pearlite structure. The content of alloying elements at the characteristic points of the surface layer was determined, which confirmed the increased content of vanadium, carbon and boron in the base of the layer, in the eutectic regions and in the carbide phase. X-ray phase analysis revealed the presence of vanadium borides VB ₂ and V ₂ B ₃ , iron borides FeB and Fe ₂ B , and vanadium carbide VC _0.88 in the surface layer of the steel. Finely dispersed inclusions of iron borides, vanadium borides and carbides significantly increase the wear resistance of steel. Wear resistance during friction against fixed abrasive particles increased four times compared to the initial state. The disadvantage of this method is the complex procedure for preparing the vanadium-boron mixture and the high duration of the heat treatment.

The invention is aimed at solving the problem of improving the quality of coatings by forming a diffusion zone at the coating-substrate interface and the productivity of the coating formation process.

The technical result consists in expanding the arsenal of means for vanadizing, as well as in using a vanadium-containing coating (charge) and heating the surface of a carbon steel substrate with a coating, where, in order to improve the quality of the vanadized near-surface layer, a vanadium-containing coating is applied containing 50 wt.% ammonium salt 2- monoethanolamine and citric acid, 25 wt.% soot T-900 and 25 wt.% vanadium oxide V ₂ O ₅ , and heating is carried out at a temperature of 950-1325°C with an exposure of 4.5-9.5 minutes.

To achieve a technical problem and the claimed result, a vanadium-containing coating is applied to the surface of a substrate made of carbon steel 20, which, under the influence of high temperature exposure, enters into an exothermic chemical reaction with the substrate material to form chemical compounds containing α-Fe, V and V ₄ C ₃ phases, increasing corrosion resistance of steel 20.

The developed method for vanadizing the surface of a 20 carbon steel substrate is illustrated in FIG. 1-4 where:

fig. 1 - infrared spectrum of the synthesized salt HOS (O) CH ₂ C (OH) C (O) (OH) CH ₂ C (O) O ^- H ₃ N ⁺ CH ₂ CH ₂ OH,

fig. 2 - vanadization cell (2a), coating in a mortar (2b),

fig. 3 - X-ray phase analysis (XRF) of a steel 20 sample after vanadization,

fig. 4 - energy dispersive X-ray analysis (EDRA) of steel 20 before (a) and after vanadization (b).

Specific Implementation Examples

Example 1. Synthesis of ammonium salt of 2-monoethanolamine and citric acid

Mixing of 2-monoethanolamine STP TU COMP 2-198-10, citric (2-hydroxypropane-1,2,3-tricarboxylic) acid GOST 908-04 and distilled water (solvent) was carried out in a molar ratio of 1:1:1 in a liter flask when heated to a temperature of 88-98°C. The stabilization of the mixture was carried out by keeping it for at least 2 hours, followed by removal of water on a rotary evaporator when the temperature was raised to 97-100°C. After that, the resulting viscous mass of ammonium salt of 2-monoaminoethanol and citric acid was transferred to a separate container. Elemental analysis of the synthesized salt and IR spectrum confirm the formation of the compound HOC(O)CH ₂ C(OH)C(O)(OH)CH ₂ C(O)O ^- H ₃ N ⁺ CH ₂ CH ₂ OH, Table. 1, fig. 1.

The main absorption bands: 2953.7 cm ^-1 - asymmetric, 2918.6 cm ^-1 - symmetrical stretching vibrations of CH ₂ groups; 1704.1, 1633.0, 1575.2 and 1404.4 cm ^-1 - anion of the ester group -C (O) O ^- , 3500-3400 cm ^-1 -cation -NH ₃ ⁺ - groups, 1780.2 cm ^{- 1} - carbonyl group C=O.

Example 2. On a standard sample (the distal end of a 10 * 8 * 2 mm rod with a total length of 28-30 mm, with a diameter of 8 mm, see Fig. 2a) made of structural quality carbon steel 20 according to GOST 1050-88, a coating layer was applied, consisting of a mixture of synthesized ammonium salts in a ratio of 50 wt. % salt, 25 wt. % soot T-900 according to GOST 7885-86 (Technical carbon for the production of rubber) and 25 wt. % vanadium oxide V ₂ O ₅ according to THE 6-09-4093-75. The coating was prepared as follows: 1.0 g of carbon black and 1.0 g of vanadium oxide V ₂ O ₅ were added to 2.0 g of salt (Fig. 2b). Then, the distal end of the rod, thinned to 2 mm, was placed in a reactor, the characteristics of which are given in table. 2. Carried out slow heating to 900°C for 5-7 minutes and holding at this temperature for 5±0.5 minutes. Vanadation was carried out at 950±30°C for 4.5±0.5 minutes.

During heating of the coated sample, the salt decomposes into ammonia and then into nitrogen and hydrogen, which act as a carrier of vanadium, which is formed during the interaction of vanadium oxide with soot. Vanadium diffuses into the depth of the steel sample structure, forming a diffusion zone containing the α-Fe,V and V ₄ C ₃ phases, identified by XPA spectra, Fig. 3. X-ray diffraction was carried out on an ARL X'TRA diffractometer "Thermo Fisher Scientific" (Switzerland) by X-ray diffraction in Cu-Kα radiation (wavelength λ=0.154178 nm) with an interval of scattering angles from 5 to 90° in automatic mode at a speed shooting 2°/min. During operation, a voltage of 40 kV and an electric current of 40 mA were used. The phase analysis of sample coatings was performed using the PDXL software package using the ICDD database.

After vanadization, the sample was separated from the base of the rod by a cut, and the microhardness was measured on a PMT-3 microhardness tester both on the vanadized surface and along the cross section of the sample. The measurement results are given in table. 3.

The presence of vanadium in steel 20 is also observed according to the EDRA data, Fig. 4.

Examples 3-11. On samples of steel 20, a coating layer was applied according to example 2. The modes of conducting vanadization and the microhardness of the surface layer are given in table. 4.

As can be seen from Table 4, layers obtained at a higher temperature and holding time have the maximum microhardness compared to the initial microhardness of the starting material. Such a difference in microhardness is due to the diffusion redistribution of iron vanadides in the surface layer and the synthesis of various compounds of vanadium with carbon. On average, the microhardness after heat treatment increased by about 2.5...2.8 times from the initial value.

The advantage of the proposed method of vanadization is the possibility of non-contact heating of the surface layers of the material being processed, and the high temperature provides increased diffusion mobility of the components involved in the diffusion of vanadium into steel.

Example 12 Corrosion resistance test.

The corrosion rate v and the deep corrosion index II were determined from gravimetric measurements according to GOST (GOST 17322-71) and (GOST 5272-68), while samples of steel 20 with a diameter of 8 mm and a thickness of 2 mm were kept in a 3% aqueous solution of sodium chloride NaCl for 48 hours, tab. 5.

According to the data obtained, it can be seen that during vanadization, the corrosion resistance of steel 20 increases.

Claims (1)

A method for vanadizing the surface of a carbon steel substrate, including applying a vanadium-containing coating and heating said substrate with a coating, characterized in that a vanadium-containing coating is applied containing 50 wt.% ammonium salt of 2-monoethanolamine and citric acid, 25 wt.% carbon black T-900 and 25 wt.% vanadium oxide V ₂ O ₅ , and heating is carried out at a temperature of 950-1325°C with an exposure of 4.5-9.5 minutes.

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