RU2637736C2 - Powder thermo-reactive charge for induction welding of solid alloy - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: charge contains, wt %: flux based on boron-containing components 8-10, a composition consisting of a boron compound and providing in the process of welding the passage of self-propagating high-temperature synthesis (SHS) 13-17, carbide - the rest. The components of the charge have the granule size of <0.5 mm, and the flux based on the boron-containing components is used in a fused form. Before using the charge, 1-2% alcohol rosin solution is added to its powder to obtain a gruel-like mass and mixed thoroughly.

EFFECT: increasing the wear resistance of carbide coating by preventing the formation of a pre-eutectic structure in it.

4 dwg, 1 tbl

Description

The invention relates to the field of powder metallurgy, welding production, hardening of machine parts by surfacing, in particular to the creation of powder mixtures (charge) for induction surfacing of hard alloys such as high-alloy chromium white cast irons, as well as for wear-resistant coatings doped with boron. The invention can be used in the manufacture and repair of machinery parts and equipment for agriculture, mining, road construction and other industries.

Known powder mixture for induction surfacing (analog) [Tkachev V.N. etc. Induction surfacing of hard alloys. - M .: Mechanical Engineering, 1973. - S. 11-12], containing the following components, wt.%:

hard alloy  80 ÷ 85 borax  10 ÷ 5 boric anhydride  8 ÷ 6 silicocalcium  2 ÷ 4

The analogue composition is intended for the formation on the surfaces of parts, working bodies and tools of various reinforcing wear-resistant coatings based on hard alloys during high-frequency heating. The disadvantage of the analogue is that during induction surfacing of hard alloys such as high-alloy chromium cast irons of the Fe-Cr-C system (materials such as PS, PG, PG-US, etc.), even with the hypereutectic structure of the initial alloy, a layer with a hypereutectic structure is formed on the surface of the parts, which is 40-50% lower in wear resistance than compact material. After melting the charge by analogy, the proportion of coating with a hypereutectic structure can be 80-100%.

Partially, this drawback of the analog is eliminated in the prototype - a mixture for induction surfacing [A.S. No. 1764912, IPC B23K 35/36, 1992) containing the following components, wt.%:

boron based flux 10 ÷ 20 boron carbide 2 ÷ 6 silicobarium 0.3 ÷ 1.5 hard alloy rest

Improving the wear resistance of the coating after the charge is melted according to the prototype is achieved by disperse hardening of the coating and its alloying with boron due to the introduction of superhard boron carbide into the composition of the prototype charge. However, the wear resistance of the resulting coating is insufficient for parts of machinery and equipment in agriculture, mining, road construction and other industries, since the introduction of boron carbide in the coating requires 3-5 minutes of surfacing with a temperature of 1250 ÷ 1350 ° C, which leads to the melting of the part, burnout of the fusible components of the charge, a change in the chemical composition of the base and coating. In addition, due to the high proportion of the flux part in the charge of the prototype at temperatures up to the melting of the hard alloy, there is destruction, dissolution and transfer to slag from the hardening coating not only oxides, but also the components of the charge and hard alloys. When melting the charge of the prototype, the proportion with a hypereutectic structure in the coating reaches 35-45%.

The objective of the present invention is to increase the wear resistance of a carbide coating by preventing the formation of a hypereutectic structure in the coating.

The problem is solved in that in the mixture for induction surfacing, which includes a flux based on boron-containing components and a hard alloy, components are added that ensure the passage of self-propagating high-temperature synthesis (SHS) with the release of atomic boron or with the formation of boron-containing components during the process - SHS composition .

The technical essence of the invention is the composition of the thermosetting powder mixture for induction surfacing of a hard alloy, containing fused flux based on boron-containing components and a hard alloy, additionally containing self-propagating high-temperature synthesis with the release of atomic boron or the formation of boron-containing components, in the following ratio of charge components, wt.%:

boron based flux 8 ÷ 10 components ensuring the passage of SHS (SHS composition) 13-17 hard alloy rest

The technical result of the invention is achieved due to the fact that the SHS composition, additionally introduced into the charge, in the process of self-propagating high-temperature synthesis heats both the charge and the part, which allows to reduce the thermal power to expose the surface of the part with a high-frequency electromagnetic field, reduce the temperature on the surface of the part 1100 ÷ 1200 ° С, to exclude part melting, burnout of low-melting components and reduce the change in the chemical composition of the surface hardening coating part.

In addition, the occurrence of exothermic reactions between the components of the SHS composition, for example, such:

with the release of atomic boron or the formation of boron-containing components, it causes doping with boron of both the hardened surface and the hard alloy deposited onto it during crystallization of the deposited layer. Moreover, during crystallization in the deposited coating, the formation of a hypereutectic structure and the formation of a new type of coating structure are suppressed.

The invention is illustrated by the following examples.

Example 1. The preparation of the SHS composition based on a mixture of powders of aluminum and boric anhydride. To prepare the SHS composition based on a mixture of aluminum and boric anhydride powders, aluminum powder of grades PA-1, 2 in accordance with GOST 6058-73 or aluminum powder of grades PAP-1, PAG-1 in accordance with GOST 5494-95 and boric anhydride in accordance with GOST 10068- are used. 62 or according to TU 113-07-012-90, taken in the ratio, wt.%:

aluminum powder or aluminum powder 43 ÷ 45 boric anhydride 55 ÷ 57

which ensure the occurrence of SHS according to the stoichiometric ratio of components in reaction 1.

Methodology for the preparation of the SHS composition: the initial components of the mixture are dried to a moisture content of not more than 0.2-0.5%, if necessary, crushed and sieved through a No. 025 sieve according to GOST 6613-86. To prepare 100 g of the SHS composition, 44 g of PA-1 aluminum powder or PAP-1 powder and 56 g of ground boric anhydride are weighed with a basic substance content of at least 99%. The components are mixed in a bi-cone mixer for 10-15 minutes. The finished mixture is loaded into a porcelain glass of 250 ml, add 15-20 ml of a saturated solution of SKB-R synthetic rubber in gasoline and mix until a homogeneous mass is formed. The resulting slurry mass is placed on a No. 05 sieve, spread in an even layer and allowed to dry for 3-5 minutes, after which it is rubbed through a sieve with a porcelain spoon. The finished granules are dried in air at a temperature of 20-25 ° C for 2-3 hours.

Example 2. The preparation of the SHS composition based on a mixture of powders of aluminum, boric anhydride and carbon black is carried out analogously to example 1, additionally introducing carbon black brand T900 according to GOST 7885-86, in the following ratio of composition components, wt.%:

aluminum powder or powder 40 ÷ 42 boric anhydride 52 ÷ 54 carbon technical rest

which ensure the occurrence of SHS according to the stoichiometric ratio of components in reaction 2.

The method of preparation of the SHS composition: the starting components are prepared analogously to example 1, but the carbon black is not dried and not sieved. The components are mixed according to the above ratio and granulated analogously to example 1. The finished granules are dried in air at a temperature of 20-25 ° C for 2-3 hours.

Example 3. The preparation of the SHS composition based on a mixture of powders of aluminum, boric anhydride and iron oxide (III). At the same time, they act analogously to example 1, additionally introducing iron grade K into the composition of red minicar according to GOST 8135-74, with the following ratio of composition components, wt.%:

aluminum powder or powder 30 ÷ 32 boric anhydride 20 ÷ 21 red iron rest

which ensure the occurrence of SHS according to the stoichiometric ratio of components in reaction 3.

The method of preparation of the SHS composition: the starting components are prepared, mixed and granulated analogously to example 1. The finished granules are dried in air at a temperature of 20-25 ° C for 2-3 hours.

Example 4. Preparation of a thermosetting powder mixture for induction surfacing of hard alloy. To prepare the mixture, a fused flux based on boron-containing components is preliminarily obtained, for which technical borax (GOST 8429-77) and boric anhydride (GOST 10068-62) in a mass ratio of 1: 0.66 in the form of dry powders (humidity less than 0.2- 0.5%) are mixed, calcined in a roasting pan at a temperature of 120-150 ° C for 1-2 hours, to isolate the main absorbed and part of the crystallization moisture, and then placed in a porcelain crucible and then fused in a muffle furnace at a temperature of 400-450 ° C within 0.5-1 h, for the final emission of water vapor, gas and fly their substances. The finished melt is poured onto a steel pan, allowed to cool and harden, and then crushed on a jaw crusher to pieces 10-15 mm in size. Dry materials are added to the melt obtained: SK20 grade silicocalcium according to GOST 4762-71, sodium silicate granules according to GOST R 50418-92 and welding flux AN-348- (A, AM, B, VM) according to GOST 9087-81 so that the finished the composition of the fused flux contained components in the following ratio, wt.%:

borax 30 ÷ 32 boric anhydride 18 ÷ 20 silicocalcium 8 ÷ 10 sodium silicate 2 ÷ 5 flux AN-348 rest

After introducing all the components into the mixture, the composition is placed in a ball mill and milled for 0.5-1 hours. The finished flux is sieved through a No. 05 sieve, selecting the passing fraction. Such a fused flux powder based on the ratio of boron-containing components [Tkachev V.N. etc. Induction surfacing of hard alloys. - M .: Engineering, 1973.] has the brand P-0.66 and it is stored in a sealed waterproof container for 1-2 months.

Methods of preparing a thermosetting powder mixture for induction surfacing of hard alloy

A metered amount of fused flux powder based on boron-containing components prepared according to Example 4, granules of the SHS composition prepared according to Examples 1-3 and previously sifted through a sieve No. 05 of a commercial alloy powder (PG-C27, PG-US25) are placed in a biconusal mixer , PS-14-60, etc.) and carry out their mixing for 10-15 minutes. The finished mixture does not require additional grinding, sieving or classification.

In similar conditions, the composition of the prototype based on the flux according to example 4 is also obtained, with the difference that it is not melted. The investigated compositions of the powder mixture and their components are shown in table 1.

Example 5. Hardening the surface of a steel part with a thermosetting powder charge for induction surfacing of a hard alloy. For induction hardening of the surface of the steel part of the proposed charge from sheet rolled steel 65G (GOST 1577-93), 6 mm thick, samples of size 50 × 140 × 6 mm are made, the surface of which is cleaned with a paper sandpaper with grain 50 in accordance with GOST 6456-82. To the selected composition of the charge add 1-2% alcohol solution of rosin to obtain a mushy mass and mix thoroughly. The prepared composition through a cardboard stencil, 3-5 mm thick, is applied to a steel plate and dried in air at a temperature of 20-25 ° C for 20-30 minutes.

A mixture of compositions No. 1-5 and a mixture according to the composition of the prototype are applied to the samples, with a distance between them of 2-3 mm. The samples thus prepared are placed in a single-loop inductor connected to an ELSIT-100 / 0.66 inverter and cooled with tap water, and they perform high-frequency heating at a frequency of 66 kHz, first to the ignition temperature of the SHS compositions at 600-620 ° C for 24- 26 s, and then another 40-60 s to the melting temperature of the hard alloy 1100-1200 ° C, after which the inductor is turned off.

The surface temperature of parts during the entire time of high-frequency heating was controlled by a chromel-alumel microthermocouple ой 0.75 mm connected to a recording device based on a Pentium-4 PC and the AEB MB110-2A ADC. The microstructure of carbide coatings was studied in metallographic thin sections after etching with 5% alcohol solution of nitric acid using an Olympus GX-51 microscope. The phase composition of the coatings was determined by X-ray microanalysis on a Philips SEM-515 scanning electron microscope equipped with an EDAX ECON-IV microanalyzer. The microhardness of the coatings was determined on a KMT-1 device. The wear resistance of the coatings was determined on a laboratory setup with friction against a non-fixed abrasive according to GOST 23.208-79.

The invention is also illustrated by the following drawings.

In FIG. 1 shows a thermogram of heating samples hardened by the proposed mixture according to example 5. In FIG. 2 shows the microstructure of the coating obtained from the composition of the prototype charge under high-frequency heating with the process parameters of example 5. In FIG. 3 shows the microstructure of the coating obtained from the proposed composition of the mixture No. 1. In FIG. 4 shows the microstructure of the coating obtained from the proposed composition of the mixture No. 5.

The technical result of the invention is to increase the wear resistance of the carbide coating by eliminating the formation of a pre-eutectic structure in it, changing the formation mechanism and forming a new coating structure when using the proposed powder mixture.

The elimination of the formation of a hypereutectic structure is achieved by reducing the maximum temperature on the surface of the part to 1200 ÷ 1250 ° C (see Fig. 1), which is achieved by additional heat input during SHS between components specially introduced into the mixture (Al + В ₂ О ₃ ; Al + B ₂ O ₃ + C; etc.). This prevents:

- overheating of the hardened surface by high-frequency currents and its melting;

- burnout of fusible components of steel, hard alloy and mixture;

- redistribution of carbon between the substrate and the coating;

- change in the chemical composition of the hard alloy;

- growth of dendrites.

The change in the mechanism of coating formation is achieved through the use of not flux but fused flux based on P-0.66 boron-containing components, granulating it to particles with a size of <0.5 mm and mixing with other charge components also having a particle size of <0.5 mm, and also due to the introduction into the mixture of components that cause the passage of self-propagating high-temperature synthesis with the release of atomic boron or the formation of boron-containing phases.

The use of fused flux eliminates the evaporation of absorbed, inclusive and crystallization water during the surfacing process, which reduces the temperature and increases the heating time at the initial stages of the charge melting, and also ensures uniformity of the coating chemical composition.

The use of all components of the charge in the form of granules with an equal particle size of the main fraction <0.5 mm eliminates their redistribution in the charge during storage, filling and melting, increases the sedimentation resistance of the melt, and eliminates the formation of a layered coating structure.

SHS composition, providing the release of a large amount of heat, accelerates surfacing.

The formation of a new coating structure is achieved due to the fact that the atomic boron released during SHS or the resulting boron-containing phases (B ₄ C, Fe-B, AlB ₁₂ ) dope with boron both the hardened surface and the hard alloy, and form closed regions of new phases in the coating (Fe _x C, Fe ₃ C, Fe ₃ (C, B), Fe ₂₃ (C, B) ₄ , Fe ₂₃ Mn (Cr) C ₄ , etc.), uniformly distributed over its volume.

Boroning a hardened metal surface also changes the state of its interface with the coating (see Figs. 3-4). At the same time, as can be seen from FIG. 2, during the induction surfacing of the GTG-US25 hard alloy from the prototype charge, two layers are formed in the coating, the lower one containing a significant amount of dendrites, with a pre-eutectic structure and forming a clear boundary with the base metal, and the upper one, with the eutectic structure, containing carbide inclusions.

The optimal composition of the thermosetting charge for induction surfacing of a hard alloy containing 8-10 wt.% Flux based on boron-containing components, 13-17 wt.% SHS composition according to examples 1-3 and the rest is a hard alloy, determined on the basis that:

- with a decrease in the flux content of less than 8 wt.% is not achieved complete wetting of the metal surface;

- with an increase in the flux content above 10 wt.%, partial dissolution and transition to the metal slag of the hardened surface and the hard alloy occurs;

- when the content of the SHS composition is reduced to less than 13 wt.%, oxidized areas appear on the hardened surface, and areas with a hypereutectic structure are preserved in the coating;

- with an increase in the content of the SHS mixture above 17 wt.%, excessive heat release, spraying of the mixture, SHS products and slag occurs, which leads to a deterioration in the quality of the coating.

The hardness of the coatings obtained during the implementation of the invention is 850-1200 FTV, the thickness is 1-3 mm, the wear resistance is 0.01-0.03 g per 10,000 m of the friction path along a non-fixed abrasive.

Claims (3)

A thermosetting powder mixture for induction surfacing of a hard alloy, containing a flux based on boron-containing components and a hard alloy, characterized in that it additionally contains a composition including boron compounds and providing self-propagating high-temperature synthesis (SHS) during the surfacing process, in the following ratio of the charge components, wt.%: boron based flux  8-10 SHS composition  13-17 hard alloy  rest while the components of the charge have a granule size <0.5 mm, and a flux based on boron-containing components is used in fused form.

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