RU2524471C2 - Spark-erosion alloying of steel part surfaces - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to electrophysical and electrochemical treatment, particularly, to spark-erosion alloying of steel part surface. In compliance with this invention, first, steel part surface is coated with antifriction coat of copper under conditions whereat shot-circuit current J_sc=0.5-0.6 A, idling voltage U_id=56.1 V, reservoir capacitor capacity C=20 mcF. Then, ply of the coat of wear-resistant high-hardness of metal or its carbide selected from then group of Ti, V, W is applied under conditions whereat short-circuit current J_sc=2.0-2.2 A, idling voltage U_id=68.7 V, reservoir capacitor capacity C=300 mcF.

EFFECT: higher hardness, wear resistance, decreased surface roughness.

5 tbl, 4 dwg

Description

The invention relates to the field of electrophysical and electrochemical processing, in particular to methods of electroerosive alloying (EEL) of the surfaces of steel parts.

A known method of electroerosive alloying, with which you can change the hardness of the metal surface:

- increase the hardness by applying to the surface of a material of higher hardness or by diffusion introduction into the surface layer of the necessary chemical elements from the environment or from the anode material;

- reduce hardness by applying softer materials to the surface;

- increase the hardness during processing of non-hardened, but hardened material, using pulses with higher energy or longer, heating the metal slightly deeper than the total thickness of the deposited and diffusion layers [Lazarenko N.I. Electrospark alloying of metal surfaces. - M.: Mechanical Engineering, 1976. - c.l9].

There is a method of electroerosive alloying with carbide and boride compounds of refractory metals, which in most cases are obtained by the cermet method. Sometimes these metals have a certain amount of metal binder. They form a good coating layer and, due to their low chemical activity, are less sensitive to the composition of the environment and the base material. Such coatings give the surface high wear resistance and hardness. However, their relatively high coefficient of friction (0.3-0.7) does not allow the use of these coatings for friction parts [Lazarenko NI Electrospark alloying of metal surfaces. - M .: Engineering, 1976. - p.13].

There is a known EEL method in which the coating layer is initially applied with an anti-friction low-melting metal selected from the group In, Sn, Cd, Pb. Then, a layer of wear-resistant high-hardness metal or its carbide selected from the group Ti, V, W is applied to the resulting coating.

This order of application of the coating layers contributes to the melting of the originally applied coating of low-melting metal when applying the second layer, filling it with microroughnesses and pores of the main coating. The crystallization of the second layer is slower due to the accumulation of heat by the melt of the low-melting metal. The surface roughness decreases to Ra = 0.6-0.8 μm. At the same time, the wear resistance of the surface increases by 3-6 times [A.S. 1734968 USSR, V23H 9/00. The method of electroerosive alloying./ VBTarelnik, E.A. Kolomycev, L.A. Ivanov, A.G. Marchenko, V.I. Taradonov, V.F. Rudenko, Yu.A. Serobabin, G.N. . Anisimov. - declared. 09/20/88; publ. 05/23/92, Bull. No. 19.], Prototype.

A further description of the invention includes references to illustrative material,

Where

figure 1 shows the microstructure of the surface layer of steel P6M5 with CEC: (a) In + BK8, (b) In + T15K6, (c) In + Cr, x 400,

figure 2 presents the microstructure (a) and the distribution of microhardness along the depth of the layer (b) KEP In + W steel 07X16H6, x 400,

figure 3 shows a device for testing samples for wear resistance (1 - sample for testing; 2 - counterbody; 3 - device for testing),

figure 4 shows the counterbody for testing the samples for wear resistance.

As a result of metallographic studies of samples of steel P6M5, 07Kh16N6 and steel 45 with the above combined electroerosion coatings (CEP), it was found that the use of low-melting metals selected from the group In, Cd, Sn, Pb as a technological coating, followed by EEL with wear-resistant refractory materials leads to a decrease not only in the roughness of the surface layer, but also in microhardness.

For example, figure 1 shows the structure of the surface layer of high-speed steel P6M5 with various CEC: In + VK8 (a). In + T15K6 (b) and In + Cr (c). EEL of the samples was carried out on a UILV-8 installation, with In being applied on the 1st mode (short circuit current, J _{to s} = 0.5 ... 0.6 A; open circuit voltage, U _xx = 38.5 V; storage capacitor capacitance, C = 20 μF), and VK8, T15K6 and chromium carbide in the 5th mode (J _{to s} = 2.0 ... 2.2 A; U _xx = 68.7 V; C = 300 μF ) Measurement of the microhardness of the In + VK8 coating shows that regions with a structure like a dispersed eutectic have a microhardness of N _µ = 7850 MPa, light, non-etched areas H _µ = 6700 MPa. Against their background, there are light inclusions with H _µ = 9700 MPa. In the In + T15K6 sequence, bright, non-etched fields have a microhardness of N _µ = 6700-7800 MPa, gray fields are 6700 MPa, light inclusions are N _µ = 13000-16600 MPa. The results of microhardness measurements as they deepen from the CEC surface are listed in Table 1.

Table 1 The results of metallographic studies of CEC on R6M5 steel Coating material Thickness, microns Microhardness, N _µ , MPa layer transition zone layer transition zone the basics In + VK8 twenty 40 6400, 6400 7040, 8900, 8300 850 In + T15K6 thirty 40 7800, 8300 8300, 8300, 8300 Also In + Cr twenty thirty 5700, 7450 7850, 8000 Also

A similar situation occurs when applying the CEC on stainless steel 07X16H6. Figure 2 shows the structure of the surface layer of steel 07X16H6 (a) and the distribution of microhardness along the depth of the layer (b) during the formation of CEC In + W. The doped layer is almost not visible. In this case, quenching occurs with austenite formation of the directly outer layer of the substrate, which leads to a significant decrease in microhardness. Then the hardness rises and already at a depth of 50 ... 80 microns corresponds to the hardness of the base metal.

When EEL became 45 tungsten carbide, the microhardness, as it deepens from the surface of the sample, with a "step" of 10 μm, is in a row: 12500, 11000, 4700, 3300, 2800 MPa, and with the initial EEL indium, then tungsten carbide - 2000, 2500, 3800, 2800 MPa.

Experience shows that the microhardness of CECs formed using not only In but also low-melting metals such as Cd, Sn, Pb as a technological coating is not high enough.

Therefore, the technical problem of increasing hardness, wear resistance and reducing the surface roughness of steel parts remains relevant and requires further research, and the present invention offers one way to solve it.

The stated technical problem is solved by creating a method of electroerosive alloying of the surfaces of steel parts, including, like the prototype, applying to the surface an antifriction coating of low-melting metal and a wear-resistant, high-hard coating by refractory metals or their carbides, in which a coating layer of copper is first applied in the modes at which the short circuit current J _kz = 0.5 ... 0.6 A, open circuit voltage U _xx = 56.1 V, the capacitance of the storage capacitor C = 20 μF, and then the wear layer high-hardness metal or its carbide selected from the group Ti, V, W, in modes in which the short-circuit current J _kz = 2.0 ... 2.2 A, open circuit voltage U _xx = 68.7 V, the capacitance of the storage capacitor C = 300 μF.

It is known that with EEL of fusible metals and their alloys, the cathode gain (details) for the entire processing period remains negative [Electrospark alloying of metal surfaces / Gitlevich AE, Mikhailov VV, Parkansky N.Ya., Revutsky VM - Chisinau: Stinza, 1985. - P.46].

In the case under consideration, as a result of the EEL of a steel substrate by a fusible metal, the liquid phases of the electrode material interact at the cathode, contributing to the establishment of a chemical bond between them and the development of bulk self-and heterodiffusion processes, the formation of intermetallic compounds, alloys, pseudo-alloys, mechanical mixtures, etc. Typically on the surface, a newly formed layer consists of anode material with a gradual decrease in concentration as it deepens. Therefore, subsequent alloying of the newly formed layer of fusible material with wear-resistant, more refractory material is hampered by the physics of the EEL process itself.

Since the EEL process occurs through a liquid bath, for the implementation of stable mass transfer of wear-resistant refractory material, it is necessary that it proceeds under alloying conditions sufficient to melt the previously deposited layer of low-melting material.

It follows that the microhardness of the CEC to a large extent depends on the amount of soft, more fusible material in the technological sublayer (originally applied layer of a soft, antifriction metal).

Given the fact that the most stable results on mass transfer are ensured by EEL of metal surfaces with copper [Tarelnik VB Quality management of surface layers by combined electroerosive alloying. - Sumy, 2002. - MacDen. - S.107-108], metallographic studies to determine the effect of the amount of the soft component in the CEC on the microhardness of the surface layer were carried out using copper as a technological sublayer.

In order to determine the effect of the most rational amount of the soft component (copper) in the CEC on the structure of the formed coatings, copper was applied to samples of steel 45 (10 × 10 × 10 mm in size) heat-treated for hardness 2800 MPa in different alloying modes. EEL samples were produced on the installation "UILV-8." The doping time of the samples was 1 min / cm ² . In this case, the samples were carefully weighed on an analytical balance "VLA-200" before and after alloying. Doping regimes and weight gain of the samples are summarized in Table 2.

table 2 Weight gain of 45 steel alloyed with copper The capacity of the storage capacitor, C, microfarad Short circuit current, J _{short circuit} , A Open circuit voltage, U _ХХ , B The weight gain of the sample, g · 10 ⁴ / cm ² twenty 0.2-0.4 38.5 28.46 twenty 0.5-0.6 56.1 51.26 300 1.6-2.0 56.1 115.3 300 2.0-2.2 68.7 156.3

After that, in the second layer, on all samples in the 5th mode (J _{to s} = 2.0 ... 2.2 A; U _xx = 68.7 V; C = 300 μF), a wear-resistant refractory material was applied - a VK8 hard alloy. Then on the device profilograph-profilometer mod. 201 of the Caliber plant, the roughness of the formed coatings was measured, thin sections were prepared, and metallographic studies of the structure were performed using a Neofot-2 optical microscope. The microhardness distribution over the depth of the surface layer was measured on a PMT-3 microhardness meter by indenting the diamond pyramid under a load of 0.05 N.

Table 3 shows the results of measuring the depth of the layer and the diffusion zone, as well as the microhardness and roughness of the formed coatings. For comparison, one of the samples (see Table 3) of steel 45 was coated with a CEC in the sequence: VK8 + Сс carbide, and the carbide was deposited in the 5th mode (J _KZ = 2.0 ... 2.2 A; U _xx = 68.7 V; C = 300 μF), and copper in the 3rd mode (J _kz = 0.5 ... 0.6 A; U _xx = 56.1 V; C = 20 μF).

The best indicators of roughness and microhardness of the surface layer are possessed by CEC with a copper sublayer deposited in the 3rd mode (J _{to s} = 0.5 ... 0.6 A; U _{X X} = 56.1 V; C = 20 μF) and the main coating of VK8 hard alloy deposited in the 5th mode (J _{to s} = 2.0 ... 2.2A; U _{X X} - 68.7 V; C = 300 μF).

Table 3 The results of metallographic studies of CEC on steel 45 with different copper contents The weight gain of the sample, g · 10 ⁴ / cm ² Thickness, microns Microhardness, MPa Roughness, Ra, microns layer transition zone layer up transition zone 28.46 10-20 twenty 4480 2200-2600 1.8 51.26 15-25 25 10490 2300-3570 0.5 115.3 5-10 10 6420 2000-3700 0.6 156.3 10-20 twenty 4790 1920-2300 0.8 23.17 * 15-30 5-10 2500, 11500 3300-4300 2,4

* Copper coating was applied with a second layer after VK8 hard alloy.

The main indicators of the EEL process (productivity, layer thickness, uniformity, etc.) are determined by the discharge energy Wu, which is understood as the energy stored in the working capacitor and determined by the formula

$$W_{\mathrm{and}}=k\cdot \frac{C\cdot U^2}{2},(\mathrm{one})$$

where k is the coefficient taking into account losses in the circuit (k = 0.5-0.6); C is the capacity of the storage capacitor; U is the open circuit voltage.

Thus, taking into account the values of the loss coefficient in the circuit, copper was deposited at discharge energy W _u = 0.016-0.019 J, and VK8 carbide at W _u = 0.354-0.425 J.

When applying initially a refractory coating, then copper, the microhardness of the surface layer is small (N _µ 2300-2500 MPa). The depth of propagation of a layer with such a microhardness is up to 30 microns. Then, as it deepens, there is a layer with a thickness of 5-10 μm with a higher microhardness (N _µ = 8000 ... 12300 MPa) and then a transition zone with a microhardness H _µ = 3300 ... 4300 MPa. Occasionally, areas with high microhardness (up to H _µ = 11500 MPa) are found on the coating surface. This is most likely the microhardness of the peaks of the protrusions of the previously deposited coating — VK8 hard alloy. The roughness of CECs formed according to the VK8 + C _u scheme reaches 2.4 μm.

Thus, in order to increase microhardness and reduce roughness in the surface layer of hardened parts, it is proposed to initially apply a layer of “technological” coating with a soft, antifriction metal with copper, and then a layer of hard wear-resistant metal or its carbide selected from the group Ti, V, W. Moreover, copper is applied in the 3rd mode (J _{to s} = 0.5 ... 0.6 A; U _xx = 56.1 V; C = 20 μF), and the wear-resistant high-hard metal - in the 5th mode (J _{K S} = 2.0 ... 2.2 A; U _xx = 68.7 V; C = 300 μF).

Metallographic studies of CEC by the proposed method show that their microhardness is at a relatively high level (8400 ... 12300 MPa). It should be noted that on top of the coating is a copper film 1 ... 2 μm thick. All coatings formed by the proposed method have a characteristic copper color. The presence of copper both on the surface and in the depth of the coating is confirmed by X-ray diffraction analysis.

Copper has a lower melting point (T _pl. = 1083 ° C) than the metals of the main coating (T _pl. = 1672 ... 3410 ° C). During crystallization, a structure of the type of a mechanical mixture is formed with a partial formation of a solid solution.

This order of application of the coating layers contributes to the melting of the originally applied coating of a more fusible copper metal when applying the second layer, filling it with microroughnesses and pores of the main coating. The crystallization of the second layer occurs more slowly due to the accumulation of heat by the copper melt, while the surface roughness decreases to Ra = 0.5 ... 0.9 μm.

Metallographic studies of CEC deposited on steel 45 by the proposed method are summarized in table 4.

Table 4 CEP Metallographic Studies Material Microhardness, MPa Roughness coverings layer Transition zone surface Ra, microns Uncoated (steel 45) 2800 2800 0.23 Ti 10800, 9600 3700, 3100 2.81 Ti + Cu 2500, 2500, 9500 3600, 3120 2.80 Cu + Ti 10500, 10500 4800, 3700 0.90 V 8500, 7300 3800, 3300 3.19 V + cu 2300, 2300, 8200 3800, 3300 2.80 Cu + V 8400, 7800 3900, 3300 0.80 W 9500, 8200 3800, 3400 3.26 W + cu 2500, 2500, 8100 4300, 3600 3.14 Cu + W 9500, 9100 3700, 3200 0.65 Tic 12000, 11500 3900, 3300 3.07 TiC + Cu 2500, 2500, 9500 3600, 3400 2.91 Cu + TiC 12000, 11500 3900, 3300 0.82 Vc 10000, 9000 4200, 3200 3.16 VC + Cu 2400, 2400, 9000 4200, 3400 2.80 Cu + VC 10500, 9600 3900, 3200 0.62 we 12500, 11000 4700, 3300 2.96 WC + Cu (a) 2350, 2350, 12300 4190, 3300 2.81 we + Cu (b) 11500, 10490 4760, 2860 2.81 Cu + WC 12300, 10490 3570, 3300 0.48 In + WC 1970, 2500 3860, 3570 0.52 Pb + WC 2600, 3969 3700, 3300 0.56 Cd + WC 2300, 3800 3600, 3300 0.77 Sn + WC 2000, 3500 4200, 3100 0.59

For a qualitative assessment of the wear resistance of CECs used to increase the operational characteristics of the surface layers of parts, the express method was used, which was carried out using an installation mounted on the basis of a vertical-drilling machine model 2M-112.

The linear wear of rectangular steel samples measuring 15 × 15 × 8 mm with CEC working in tandem with 4K-20 fluoroplastic was determined by the method of artificial bases by the difference in the depths of the prints deposited on a Vickers device. The samples were alternately mounted in the device 3 (abu.3), located on the machine table, which provided self-alignment of the sample plane relative to the plane of the counterbody end face.

The counterbody is a cylindrical sample (Fig. 4) made of 4K-20 fluoroplastic. It is fixed in the spindle of the machine. The installation contains a time relay, which records the test time and reverse spindle rotation. Counterbody load

is 100 N.

To assess the wear, four recesses are applied to the sample according to the template by pressing an indenter of a Vickers or PMT-3 hardness tester. The recesses are placed in a circle in the middle diameter of the counterbody in diametrically opposite sides.

To determine the amount of wear before and after the tests, we measured the diagonal length (d) of the recesses located perpendicular to the velocity vector. The average linear wear of the sample was determined according to formula (1).

The average linear wear, microns

$$\Delta h_{\mathrm{from}R.}=\frac{\Delta h_{\mathrm{one}}+\Delta h_2+\mathrm{<figure-callout\; id="3"\; label="\Delta \; h"\; filenames="00000005.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{h}_{}{}_3+\Delta h_{\mathrm{four}}}{\mathrm{four}},(\mathrm{one})$$

where Δh ₁ , Δh, Δh ₃ , Δh ₄ - linear wear of the samples, respectively, in each of the four points, microns. The test time for samples per kilometer at 2500 rpm spindle is 16 minutes

To develop the technology of applying the CEC and to check their wear resistance, steel 45 samples were used with coatings of hard wear-resistant and soft antifriction materials applied in different sequences. The test results are listed in table 5.

Table 5 The effect of the EEL sequence by electrodes of soft antifriction and hard wear-resistant metals and their carbides on the wear resistance of steel samples 45 Coating material Linear wear (Δh) of the sample for 320 min of testing, μm main * technological Without technological Followed by technological With previous technological

* * * coverings coating coating Ti *** *** 2,4 V *** *** 2.6 W In *** *** 1.2 Tic *** *** 2.5 Vc *** *** 2.6 WC *** *** 2.2 Ti *** *** 4.8 V *** *** 4.6 W Sn *** *** 4.3 Tic *** *** 5.1 Vc *** *** 3.8 WC *** *** 4.2 Ti *** *** 1.4 V *** *** 1.7 W Cd *** *** 0.9 Tic *** *** 1.2 Vc *** *** 1.6 WC *** *** 1.3 Ti *** *** 3.8 V *** *** 4.6 W Pb *** *** 3.2 Tic *** *** 2.8 Vc *** *** 4.7 WC *** *** 3.3 Ti *** *** 0.9 V *** *** 0.8 W Cu *** *** 1.2 Tic *** *** 0.82 Vc *** *** 0.62 WC *** *** 0.8

* J _{to s} = 2.0 ... 2.2 A; U _xx = 68.7 V; C = 300 microfarads;

** J _{to s} = 0.5 ... 0.6 A; U _xx = 38.5 V; C = 20 microfarads.

*** it was not possible to obtain the results of studies of the wear resistance of the samples due to their high roughness Ra = 2.28 ... 3.41 μm and, as a result, the catastrophic wear of the counter-sample from fluoroplastic.

Thus, on the basis of the conducted studies, CECs formed in the sequence when copper is applied as the first layer and hard wear-resistant metal as the second is recommended for practical use.

Claims (1)

A method of electroerosive alloying of the surfaces of steel parts, including applying an antifriction coating of low-melting metal and a wear-resistant, high-hard coating by refractory metals or their carbides to the surface, characterized in that the coating layer of copper is first applied in modes in which the short-circuit current J _kz = 0, 5-0,6 a, idling voltage U _x = 56.1 The storage capacitor and the capacitance C = 20 uF, and then a coating layer of wear-resistant high hard metal or carbide selected from c ppy Ti, V, W, on the modes in which the short circuit current J _sc = 2.0-2.2 A, open circuit voltage U _xx = 68.7 V and capacitance of the storage capacitor C = 300 uF.

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