RU2696616C1 - Method of aluminizing steel parts - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to electrophysical and electrochemical treatment, in particular, to electroerosion alloying of steel parts surfaces with aluminum and sulfur, and can be used for treatment of surfaces of heat-treated steel parts. Method for aluminizing a steel part involves electroerosion alloying of a steel part surface with an aluminum electrode at discharge energy W_p=0.52–6.8 J and capacity 1.0–3.0 cm²/min. At that, before electricerosion alloying on surface of part subjected to aluminizing, sulfuric ointment containing 33.3 % of sulfur and added aluminum powder is applied, after which, without waiting for drying of applied ointment, aluminizing process is performed.

EFFECT: invention increases hardness and wear resistance of aluminize steel parts, as well as prevents setting during friction and improved resistance to atmospheric corrosion.

1 cl, 3 dwg, 3 tbl

Description

The invention relates to the field of electrophysical and electrochemical processing, in particular, to electroerosive alloying (EEL) of the surfaces of steel parts with aluminum (aluminizing) and sulfur (sulfidation) and can be used for treating surfaces of heat-treated steel parts.

There is a method of sulfidation, which is a thermochemical process for processing products made of iron-based alloys to enrich the surface layers with sulfur. The effect of sulfidation is reduced to the formation of a sulfide film on the surface of the part. Sulfides increase the surface activity of metals and alloys, and also provide wetting with surface-active substances and improve the setting resistance. A sulphide film having a lower strength than the base metal is easily destroyed by friction and is separated from the base without plastic deformation, preventing the setting of friction surfaces. The film of iron sulfide (FeS) increases the wear resistance of rubbing surfaces and improves their working life. The ferrosulfide coating has a fairly high porosity and absorbs a large amount of lubricant, giving the material the property of self-lubrication [Glossary-reference book on friction, wear and lubrication of machine parts / V.D. Zozulya, E.L. Shvedkov, D.Ya. Rovinsky, E.D. Brown Repl. Ed. THEM. Fedorchenko. USSR Academy of Sciences. Institute of Materials Science. - 2nd ed., Revised. and add. -Kiev: Science, Dumka, 1990. - p. 203.].

A known method of alitization [M.A. Elizavetin, E.A. Satel. Technological methods to increase the durability of machines. M .: mechanical engineering, 1969. - 400 s], including the deposition of an aluminum layer on a steel surface (usually by spraying), coating and annealing. Particular attention is paid to the roughness of the aluminized surface, and oxide films, oil and dust are unacceptable. The spray of aluminum particles should be large, which accelerates the diffusion of aluminum into the surface layer of the metal during annealing. The coating is applied to the surface in a continuous layer in two to three steps and strictly observe the regime of thermal diffusion treatment, which preserves the coating layer. After applying the aluminum coating and coating, thermal diffusion saturation of the surface layer is carried out: the component is annealed. The initial temperature is 600-650 ° C, then fast heating is carried out to 900-950 ° C with a holding time of 2.5-3.5 hours, after which the part is slowly cooled together with the furnace to a temperature of 500-550 ° C, and then in the air . The thickness of the coating with molten aluminum depends on the operating temperature of the part: for a temperature of 700-800 ° C, the coating thickness is 0.2-0.3 mm, and for a temperature of 900-1000 ° C it is 0.5-0.7 mm. After metallization with aluminum, the part is covered with a 10-20% solution of aluminum chloride, then coated with liquid glass, sprinkled with quartz sand and dried at a temperature of 100 ° C. The dried part is again coated with liquid glass and dried again. At a temperature of 600-700 ° C, the part is loaded into the furnace and heated to a temperature of 1200-1250 ° C with a holding time of 14-40 minutes, after which it is slowly cooled first in the furnace to a temperature of 800 ° C. and then in the air.

Alitized low-carbon steel is more heat-resistant than special heat-resistant steel 4X14H14 B2M. Alification of the surface of a mold from St.Z. when casting a tool from P18 high-speed steel at a pouring temperature of 1480-1500 ° C showed that such molds withstand more than a hundred castings without visible damage to the surface aluminized layer.

Along with positive results, the technology described above has several disadvantages:

- high cost and complexity of the process;

- the need for control at all stages of the technology;

- heating of the entire part, and, accordingly, structural changes in the metal;

- leashes and warping;

- the duration of the process is more than 8 hours;

- high power consumption;

- negative impact on the environment, etc.

In [Khimukhin S.N., Astapov I.A., Teslina M.A. [and others] The formation of heat-resistant coatings by the method of electrospark alloying using Ni-Al intermetallic alloys // Engineering - from theory to practice: collection of works. Art. by mater. XV int. scientific - prakt. conf. - Novosibirsk: SibAK, 2012], the effect of the composition of synthesized Ni-Al alloys on the formation of coatings obtained by the method of electrospark alloying on stainless steel 30X13 was studied. The phase composition of the coatings was studied; the results of metallography and heat resistance tests are presented. It is shown that the most effective for creating heat-resistant coatings is the synthesized alloy of the composition Ni-66.9% Al-32.9%.

The disadvantages of this technology include the need for the synthesis of alloys of the composition Ni-66.9% Al-32.9%. Alloys with a different composition do not lead to positive results. In addition, the ESA process should be carried out in a protective atmosphere of argon, which requires additional costs for the manufacture of special equipment.

In accordance with the work [S.A. Pyachin, A.A. Burkov, V.S. Komarova. Formation and research of electrospark coatings based on titanium aluminides. // Surface. X-ray, synchrotron and neutron studies, 2013, No. 6, p. 16-24], electrospark deposition of titanium on aluminum and aluminum on titanium created coatings containing Ti-Al intermetallic compounds. Applying the methods of electron microscopy, X-ray diffraction and X-ray spectral analysis, the structure and composition of the coatings were studied. It was established that, regardless of the duration and frequency of the discharge pulses, the surface layer formed in argon mainly contains the α-TiAl ₃ intermetallic compound. The phases γ-TiAl and α ₂ - Ti ₃ Al can be obtained by deposition of aluminum on titanium, followed by deposition of a second layer of titanium. When electric spark coatings are formed in air, aluminum oxide and titanium nitride are additionally formed. This technology is also performed in a protective environment, for example, argon and is used only for parts made of titanium.

The experience of forming aluminum coatings on steel substrates involves the use of EEL technology (the same as EIL), based on the transfer of metals from the anode to the cathode under repeated exposure to electric discharges. Compared to others, this technology has several advantages. These include: the simplicity of the technological operation of the deposition of metals in a gaseous medium at atmospheric pressure, the formation of a uniform surface layer by mixing in the molten state materials used as electrodes, and high adhesion of the coating to the substrate.

There is a method of sulfocementation by electroerosive alloying with a graphite electrode of a steel surface of a product, in which immediately before alloying with a graphite electrode a grease containing sulfur is applied to the steel surface [UA 119318 U, В23Н 1/00, В23Н 9/00, С23С 8/60, 2017].

The main disadvantage of this method of sulfo-cementation is: the inability to protect the part from oxidation at high temperatures (700 - 900 ° C and above), as well as from atmospheric corrosion and sea water.

на корисну модель UA 119316 U МПК (2017.01) С23С 10/48 (2006.01) В23Н 9/00. Cпociб обробки поверхонь сталевих деталей/ Тарельник В.Б. Марцинковський B.C. Бшоус А.В. Гапонова О.П. Коноплянченко

В. Антошевський Б. Кундера Ч. Жуков О.М. - №u201701845; заявл. 27.02.2017; опубл. 25.09.2017. - Бюл. №18/2017] (Прототип). Следует отметить, что при данном способе обработки максимальная толщина алитированного слоя получена при наибольшей энергии разряда W_p=6,8 Дж и равна 70 и 130 мкм, соответственно, на подложках из стали 20 и 40, что не всегда достаточно для защиты от разрушения поверхностей стальных деталей, подвергаемых воздействию высоких температур. Кроме того, при сухом (без смазки) контакте алитированной таким способом поверхности детали возможно схватывание, заедание, микросваривание и вырыв отдельных участков поверхности [UA 119316 U, С23С 10/48, В23Н 9/00, 2017].Closest to the claimed method is a method of aluminizing steel parts by electroerosive alloying (EEL) with an aluminum electrode at a discharge energy of W _p = 0.52 - 6.8 J and a productivity of 1.0 - 3.0 cm ² / min. The method provides the formation of a so-called white (alitized) layer with a thickness of 70-130 μm, respectively, with a microhardness of 5,000 - 7,500 MPa, a roughness (Ra) of 6-9 μm and a continuity of 95-100%. [Patent

for cinnamon, model UA 119316 U IPC (2017.01) С23С 10/48 (2006.01) В23Н 9/00. The method of processing over steel parts / Tarelnik VB Marcinkowski BC Bshous A.V. Gaponova O.P. Konoplyanchenko

V. Antoshevsky B. Kundera Ch. Zhukov O.M. - No. u201701845; declared 02/27/2017; publ. 09/25/2017. - Bull. No. 18/2017] (Prototype). It should be noted that with this processing method, the maximum thickness of the aluminized layer was obtained at the highest discharge energy W _p = 6.8 J and is equal to 70 and 130 μm, respectively, on substrates made of steel 20 and 40, which is not always sufficient to protect against surface damage steel parts exposed to high temperatures. In addition, with dry (without lubrication) contact of the surface of the part aluminized in this way, setting, seizing, micro-welding and tearing of individual parts of the surface are possible [UA 119316 U, С23С 10/48, В23Н 9/00, 2017].

The basis of the invention is the task of creating a method of aluminizing steel parts, which would increase their hardness, wear resistance, prevent setting during friction and improve the resistance to atmospheric corrosion.

The problem is solved by the fact that in the method of aluminizing a steel part, including electroerosive alloying of the surface of a steel part with an aluminum electrode at a discharge energy of Wp = 0.52-6.8 J and a productivity of 1.0-3.0 cm2 / min, according to the invention, before by electroerosive alloying, a sulfur ointment containing 33.3% sulfur and added aluminum powder is applied to the surface of the part to be aliased, after which, without waiting for the applied ointment to dry, an aliating process is carried out.

In the method, sulfuric ointment is applied with an aluminum powder content of not more than 56%.

The inventive method increases the hardness of the parts, their wear resistance, prevents setting during friction and improves the resistance to atmospheric corrosion.

Aluminized steel acquires high scale resistance (up to 850-900 ° C), since during heating, a dense film of aluminum oxide Al ₂ O _{3 is} formed on the surface of the aluminized parts, which protects the metal from oxidation. The hardness of the aluminized layer on the surface is up to 500 HV, while this provides wear resistance, a high rate of which cannot be achieved by the prototype method.

The presence of sulfur in the grease promotes the sulfidation process. In the method, alitization and sulfidation are simultaneously carried out, i.e. sulfoalithization process.

The invention is illustrated by an example of a specific implementation of the method with reference to illustrative material, where:

in FIG. 1 shows the microstructure of the surface layer;

in FIG. 2 shows the distribution of microhardness in the surface layer;

in FIG. 3 shows a profilogram of the surface layer of a sample of steel 20.

An example of a specific implementation of the method.

In order to determine the influence of the energy parameters of the EEL equipment on the quality parameters of the coatings, samples were made of steel 20 and 40 with a size of 15 × 15 × 8 mm, onto which a grease was applied in the form of a sulfur ointment with a sulfur content of 33.3%. Before application, aluminum powder PAD-0 grade (GOST 5494-95) was added to sulfuric ointment. The maximum amount of powder was 56%. A further increase in the amount of powder led to a decrease in adhesion to the surface to be aluminized. After that, without waiting for the drying of the jellied substance, EEL was produced with an aluminum electrode on the installation of the Elitron-52A model using various modes. Moreover, each EEL mode corresponded to its own discharge energy and productivity — the area of the formed coating per unit time (Table 1).

It should be noted that a decrease in the EEL performance leads to a decrease in the quality parameters of the surface layer, that is, the appearance of burns, and most importantly, the destruction of the formed layer, which especially affects more “rough” modes at a discharge energy Wp> l J. An increase in productivity leads to reduce coating continuity. As an electrode tool used rods 0 4 and a length of 45 mm from aluminum wire brand SvA99 (GOST 7871-75).

Metallographic analysis of the coatings was carried out using an MIM-7 optical microscope; durametric studies were performed on a PMT-3 device.

The surface roughness after EEL was determined using a profilograph device — mode profilometer. 201 factory "Caliber" by removing and processing profilograms.

To study the distribution of sulfur over the depth of the layer, a local X-ray microanalysis was carried out, based on the registration of characteristic x-ray radiation excited by an electron beam of chemical elements present in the microvolume. For this, an ISIS 300 Oxford Instruments electron microscope equipped with an X-ray microanalyzer was used.

According to the results of the study, Fig. 1 shows the microstructure of the surface layer formed by the EEL with an aluminum electrode with a discharge energy Wp = 6.8 J on a steel sample 20 coated with a grease containing 33.3% sulfur and 56% aluminum powder. Figure 2 shows the distribution of microhardness as it deepens from the surface.

A characteristic feature of the structure is a massive white layer, the thickness of which in some areas is from 160 to 200 microns (Figure 1). The microhardness on the surface is about 5000 MPa. As it deepens, the microhardness gradually decreases and at a depth of 170 microns passes into the microhardness of the base (1700 MPa).

In FIG. Figure 3 shows a profilogram of a portion of the sulfoalitated surface of a steel sample 20 with EEL using an aluminum electrode with a discharge energy of Wp = 6.8 J.

Thus, as a result of studies of the surface layer of the steel 20 sample after sulfoalitization, it was found that the coating continuity is 100%, the layer thickness reaches 200 μm, and the microhardness is up to 5000 MPa.

Table 2 shows the qualitative parameters of the surface layers of steel 20 and steel 40 upon sulfoalting by EEL with a discharge energy of 0.52; 2.60 and 6.80 J.

The presence of sulfur in the grease promotes the sulfidation process.

In the table. Figure 3 shows the change in sulfur content as it deepens from the surface during sulfoalting of steel 20 by EEL with a discharge energy of 6.80 J.

Claims (2)

1. The method of aluminizing a steel part, including electroerosive alloying of the surface of a steel part with an aluminum electrode at a discharge energy of W _p = 0.52-6.8 J and a productivity of 1.0-3.0 cm ² / min, characterized in that before electroerosive alloying Sulfur ointment containing 33.3% sulfur and added aluminum powder is applied to the surface of the part to be aluminized, after which the alimentation process is carried out without waiting for the applied ointment to dry. 2. The method according to p. 1, characterized in that the sulfuric ointment is applied with an aluminum powder content of not more than 56%.

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