RU2698001C1 - Method of reconditioning worn-out surfaces of parts of machines from stainless steel - Google Patents

Abstract

FIELD: physics; chemistry.

SUBSTANCE: invention relates to electrophysical and electrochemical treatment and can be used for repair of machine parts. Method involves application on worn-out surface of part of coating by electroerosion alloying (EEA) electrode from hard alloy T15K6 using energy of discharge initially Wp = 0.55 J, and then Wp = 0.90 J, applying reinforced metal-polymer material (MPM) onto obtained surface, providing its polymerisation and final mechanical processing. Prior to polymerisation MPM is reinforced with metal powder of hard alloy BK8, and after polymerisation of layer of reinforced MPM prior to final machining, its laser treatment is performed.

EFFECT: invention enables to recover worn-out surfaces of parts of machines from stainless steel, particularly 12X18H10T, and provides formation of a surface layer, quality, wear resistance, reliability and durability of which is higher than when parts are restored by EEA methods with application of MPM.

4 cl, 25 dwg, 2 tbl

Description

The invention relates to the field of electrophysical and electrochemical processing, in particular, to electroerosive alloying, and can be used for repair of machine parts from stainless steel.

The most important tasks of the repair and maintenance production are maintaining operability, restoring the resource of machines and equipment, ensuring their high reliability and the possibility of efficient use. To solve these problems, it is envisaged to improve the quality of repairs by introducing modern methods of its organization and optimal technological processes of hardening and restoration of parts. The resource of restored parts, as a rule, is significantly higher due to the use of effective methods of restoration and improved properties of hardened surfaces.

Modern hardening technology has numerous methods for improving the structure and properties of the surface layer of parts, each of which has optimal applications, advantages and disadvantages. There is a known method of electroerosive alloying (EEL), which is increasingly widely used in industry to increase the wear resistance and hardness of the surfaces of machine parts, including those working at high temperatures and aggressive environments, to increase their heat and corrosion resistance, as well as to restore worn surfaces machine parts during repair, etc.

EEL of the surface is the process of transferring material to the surface to be treated by a spark electric discharge. The method has a number of specific features:

- the anode material (alloying material) can form a coating layer on the surface of the cathode (alloyed surface) that is extremely firmly adhered to the surface. In this case, not only is there no interface between the deposited material and the base metal, but even the anode elements diffuse into the cathode;

- alloying can be carried out in strictly specified places with a radius of fractions of a millimeter or more, without protecting the rest of the part;

- the technology of electroerosive alloying of metal surfaces is very simple, and the necessary equipment is small-sized and transportable [Lazarenko NI Electrospark alloying of metal surfaces .- M.: Mechanical Engineering, 1976.-ss. 3, 4, 13, 19]. It should be noted that with an increase in the EEL mode (discharge energy), as a rule, the continuity of the formed coating decreases due to the formation of through pores) [Lazarenko N.I. Electrospark alloying of metal surfaces. - M.: Mechanical Engineering, 1976.- ss. 15-17].

МПК В23Н 5/00 / Тарельник В.Б., Марцинковський B.C., Павлов О.Г.; Опубл. 25.04.2017, Бюл. №8].To improve the quality of the surface layer restored by the EEL method, the authors proposed a method in which the EEL coating is applied in at least two stages, the layer being applied at the first stage using the modes that provide the greatest continuity and thickness of the coating, then EEL is produced by the electrode with such a discharge energy and a corresponding productivity at which a surface with a roughness of approximately 2-4 times higher is formed than in the previous step. In this case, the cathode metal (part) is ejected at the places where pulses are applied, i.e. spraying of the most protruding parts of the surface, and in their place depressions of the newly formed coating are formed, the depth of which is at the level of the surface of the previous coating. As a result, there is a minimal increase in the level of surface roughness [Cnocib reinforcing the relative surfaces of metal parts: Pat. 115676.

IPC V23H 5/00 / Tarelnik VB, Martsinkovsky BC, Pavlov O.G .; Publ. 04/25/2017, Bull. No. 8].

Despite the fact that EEL has a positive effect on the wear resistance of the surface layer, its shortcomings often limit the implementation of this technology for a wide range of machine parts. Such disadvantages include an increase in the roughness of the surface of products after EEL, uneven surface hardening, the negative effect of erosion discharge on the fatigue properties of products, etc.

МПК В23Н 5/00 /Марцинковський B.C., Тарельник В.Б., Павлов О.Г., Iщенко А.О.; Опубл. 25.02.2014, Бюл. №4, -3 с].There is also known a method of restoring the surfaces of metal parts, including applying to the worn surface of a part of a coating an electroerosive alloying (EEL) with a metal electrode, in which the EEL coating is applied in modes providing a given surface roughness of the coating, then at least one layer of metal-polymer is applied to the obtained surface material (MPM), ensure the polymerization of the applied layer of MPM, after which it is subjected to finish processing [How to renew the relationship on top nn metal parts (varianti): Pat. 104664.

IPC V23H 5/00 / Martsinkovsky BC, Tarelnik VB, Pavlov O.G., Ichenko A.O .; Publ. 02/25/2014, Bull. No. 4, -3 s].

The disadvantages of this method are:

- low hardness of metal-polymer materials;

- the main purpose of the method is the restoration of parts in one-piece joints (seats for bearings, coupling halves, etc.);

- metal-polymer materials work well in compression and much worse in shear, which negatively affects their use for restoring the friction surfaces of parts;

- change in the properties of materials with increasing temperature on the friction surfaces, etc.

МПК В23Н 5/00 / Тарельник В.Б., Марцинковський B.C., Павлов О.Г., Саржанов Б.О.; Опубл. 28.08.2017, Бюл. №16].There is also known a method of restoring the surfaces of metal parts, which includes applying to the worn surface of a part of a coating an electroerosive alloying (EEL) with a metal electrode, in which the EEL coating is applied in modes providing a given surface roughness of the coating from 1 to 200 μm or more, and a given roughness is obtained by EEL modes, determined by the discharge energy of 0.036-6.8 J, then one layer of metal-polymer material (MPM) is applied to the obtained surface, but Before polymerization, the MPM is reinforced with at least one layer of wire, and, depending on the required quality parameters of the worn surface, a soft, ductile wire is wound on the surface of the parts of the bodies of revolution or put on with an interference fit in the form of a heat-treated spring, and for flat and curved surfaces are reinforced with soft or hard wire connected in the form of a mesh, then at least one layer of MPM is applied, after which this layer is subjected to finishing. Moreover, when applying a second layer to the already polymerized MPM layer, the previous MPM layer is peeled and degreased. In addition, the finishing treatment of the deposited layer of MPM can be carried out by a mechanical method, for example, grinding or blade processing, to the required depth. [How to improve the quality of metal parts: Pat. 118892.

IPC V23H 5/00 / Tarelnik VB, Martsinkovsky BC, Pavlov O.G., Sarzhanov B.O .; Publ. 08/28/2017, Bull. No. 16].

However, this method is not without drawbacks. In particular, these are:

- technological difficulties associated with fixing the reinforcing material (wire or mesh) on the restored surface;

- technological difficulties associated with the restoration of the surfaces of parts of bodies of revolution, when it is necessary to put on a piece with an interference fit a wire in the form of a heat-treated spring;

- uneven distribution of the reinforced material, both in the vertical and horizontal planes of the restored surface;

- significant heterogeneity of the structure of the surface layer, especially when restoring flat and curved surfaces, etc.

The aforementioned disadvantages are eliminated in the claimed method of restoring surfaces of stainless steel parts, in particular, grade 12X18H10T, which, as is well-known, involves applying a T15K6 hard alloy electrode using a discharge energy originally W _p = 0.55 J, and then W _p = 0.90 J, applying reinforced metal-polymer material (MPM) to the obtained surface, ensuring its polymerization and final machining, but in a cat In accordance with the present technical solution, prior to polymerization, MPM is reinforced with metal powder of VK8 hard alloy, and after polymerization of a layer of reinforced MPM, before its final machining, laser processing is performed. In this case, when reinforcing, a metal powder from VK8 hard alloy is added to the MPM in portions of 5-7% of the total amount of metal powder added, after each portion the resulting mixture is thoroughly mixed, and before applying to the EEL coating, the concentration of the powder in the mixture is adjusted to approximately up to 60%, laser processing of a layer of polymerized reinforced MPM is performed after it is dried for 24 hours. The laser processing process is carried out when the sample is supplied at 120 mm / min, the voltage of the laser source is 500-550 V, the laser pulse is 0.3⋅10 ^-3 -1⋅10 ^-3 and the pulse repetition rate is 50-100 Hz, while the thickness and the microhardness of the treated layer is increased by increasing the voltage of the laser source from 500 to 550 V, increasing the laser pulse from 0.3⋅10 ^-3 to 1⋅10 ^-3 and reducing the pulse repetition rate from 100 to 50 Hz.

In essence, the technical problem of eliminating the above drawbacks has been solved through the use of integrated technology, which includes the method of electroerosive alloying with the subsequent deposition of an MPM layer reinforced with metal powder, for example, from VK8 hard alloy, and its processing by laser.

When using the integrated technology, various options for the formation of the structure of the restored surface layer are possible.

The following is a specific example of the method with reference to schematic images, where:

- in FIG. 1 shows a sample of steel 12Kh18N10T after EEL with the T15K6 hard alloy at W _{p =} 0.55 J;

- in FIG. 2 shows a sample of steel 12Kh18N10T after EEL with the T15K6 hard alloy at W _p

= 0.55 J + W_p= 0.90 J;

- in FIG. Figure 3 shows a sample of steel 12X18H10T after EEL with T15K6 hard alloy at W _p = 0.55 J + W _p = 0.90 J, polymerization of a layer of a mixture of MPM and VK6 carbide powder;

- in FIG. Figure 4 shows a sample of steel 12Kh18N10T after EEL with T15K6 hard alloy at W _p = 0.55 J + W _p = 0.90 J, polymerization of a layer of a mixture of MPM and carbide powder VK6 and laser processing (LO) of a polymerized layer of a mixture of MPM and carbide powder VK6;

- in FIG. 5 shows a laser radiation device of the Laser Nd - YAG BLS 720 model (ROFIN-BAASEL Lasertech, Germany);

- in FIG. 6 shows the structure of steel 12X18H10T after EEL with the T15K6 hard alloy;

- in FIG. 7 shows the structure of steel 12X18H10T after EEL with T15K6 hard alloy and polymerization of the deposited layer of a mixture of MPM VK6 hard alloy powder;

- in FIG. Figure 8 schematically shows the microhardness distribution of the layers of the formed coating as it deepens from the surface: 1 - EEL with the T15K6 hard alloy; 2 - EEL with T15K6 + hard alloy (MPM + VK6 hard alloy powder);

- in FIG. 9 shows a coating portion of a hard alloy T15K6 and VK6 on steel 12X18H10T in a plane perpendicular to the formed layer, X 2000;

- in FIG. 10 schematically shows the distribution of elements in a coating of a hard alloy T15K6 and VK6 on steel 12Kh18N10T;

- in FIG. 11 shows the microstructure of a steel sample 12X18H10T in FIG. 4 processed according to mode 1;

- in FIG. 12 schematically shows the distribution of microhardness over the depth of the layer of a sample of steel 12X18H10T in FIG. 4 processed according to mode 1;

- in FIG. 13 shows the microstructure of a steel sample 12X18H10T in FIG. 4 processed according to mode 2;

- in FIG. 14 schematically shows the distribution of microhardness along the depth of the layer of a sample of steel 12X18H10T in FIG. 4 processed according to mode 2;

- in FIG. 15 shows the microstructure of a steel sample 12X18H10T in FIG. 4 processed according to mode 3;

- in FIG. 16 schematically shows the distribution of microhardness over the depth of the layer of a sample of steel 12X18H10T in FIG. 4 processed according to mode 3;

- in FIG. 17 shows the microstructure of a steel sample 12X18H10T in FIG. 4 processed according to mode 4;

- in FIG. 18 schematically shows the distribution of microhardness along the depth of the layer of a sample of steel 12X18H10T in FIG. 4 processed according to mode 4;

- in FIG. 19 shows the microstructure of the surface layer of a steel specimen 12X18H10T in FIG. 4 processed according to mode 5;

- in FIG. 20 shows the microstructure of a steel sample 12X18H10T in FIG. 4 processed according to mode 5;

- in FIG. 21 schematically shows the distribution of microhardness along the depth of the layer of a sample of steel 12X18H10T in FIG. 4 processed according to mode 5;

- in FIG. 22 schematically shows the microhardness in the surface “dark” layer depending on the laser treatment mode;

- in FIG. 23 schematically shows the microhardness in the surface “light” layer, depending on the laser treatment mode;

- in FIG. 24 schematically shows the maximum thickness of the “dark” layer depending on the laser treatment mode;

- in FIG. 25 schematically shows the maximum thickness of the "bright" layer depending on the laser treatment mode.

Samples of 15 × 15 × 8 mm in size made of stainless steel 12X18H10T by EEL on an installation of the Elitron 52-A model were gradually coated with T15K6 hard alloy electrodes using the initial discharge energy W _p = 0.55 J, FIG. 1, and then W _p = 0.90 J of FIG. 2. As the reinforcing material during polymerization, a powder was used in the form of a VK6 carbide mixture, which was added in portions of 5-7% in MPM. Moreover, after each serving, the mixture formed in the form of a paste was thoroughly mixed, bringing the concentration of powder in it before application to the EEL-formed coating to approximately 60%. A further increase in concentration made mixing difficult and did not guarantee complete enveloping of individual particles of the carbide mixture with a metal-polymer material. The grease formed in this way, carefully rubbing, was applied to the T15K6 hard alloy formed by the EEL method, FIG. 3.

After drying for 24 hours, the surface of the formed coating was laser treated (LO) using a Laser Nd - YAG BLS 720 model device (ROFIN-BAASEL Lasertech, Germany), FIG. 5 with the laser parameters below:

- maximum energy 40J,

- maximum power 150 W,

- operating frequency 0.1-500 Hz,

- pulse duration 0.1-20 ms,

- spot diameter 0.6 mm,

- wavelength 1064 nm,

- desktop: 500 × 500 mm,

- linear movement along three axes, a rotary head,

- Rotary table.

In FIG. 4 shows a sample of steel 12Kh18N10T after a phased EEL with T15K6 hard alloy at W _p = 0.55 and 0.90 J; the subsequent application of the grease from the MPM and carbide mixture VK6 and laser treatment in the modes shown in Table 1.

Laser Modes

For metallographic and durometric studies of the prepared samples, a Neofot-2 optical microscope was used, with the help of which an assessment was made of the quality of the layer, its continuity, thickness and structure of the sublayer zones - the diffusion zone and the heat-affected zone.

In addition, a durometric analysis of the distribution of microhardness in the surface layer and in the depth of the thin section from the surface was carried out. Microhardness was measured on a PMT-3 microhardness meter by indentation of the diamond pyramid under a load of 0.05 N according to GOST 9450-76.

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

At all stages of processing, the surface roughness was measured on a device of the profilograph-profilometer model 201 of the Caliber plant. The results were recorded using a special prefix.

The stage-by-stage formation of a coating of T15K6 hard alloy at W _p = 0.55 and W _p = 0.90 J provides 100% continuity. The thickness of the increment layer, measured by a micrometer on individual ledges, reaches 0.12 mm. The surface roughness in this case is Rz = 37 μm. A further increase in the discharge energy leads to an increase in the layer thickness to 0.19 mm and a significant decrease in the quality of the coating (85% continuity and Rz = 65 μm roughness).

In FIG. Figures 6-8 show the structures of steel samples 12Kh18N10T: after EEL with the T15K6 hard alloy, Fig. 6, and T15K6 EEL followed by applying a composite material consisting of MPM and VK6 carbide powder, FIG. 7, as well as the microhardness distribution of the formed coatings as they deepen from the surface, FIG. eight.

An analysis of the microstructures showed that after the EEL of steel 12X18H10T with T15K6 hard alloy, FIG. 6, the structure of the surface layer consists of three zones. On the surface there is a dark-colored zone up to 80 microns thick, the microhardness of which is in the range of 5000-5400 MPa. Below, as deepening, there is a transition zone of a lighter color, the microhardness of which gradually decreases and at a depth of ~ 200 μm corresponds to the microhardness of the base.

In the subsequent application of a composite material consisting of MPM and VK6 carbide powder, FIG. 7, the surface layer consists of 4 zones. On the surface there is a dark-colored zone up to 120 microns thick, the microhardness of which is in the range of 6200 - 9200 MPa. At the boundary with the second zone, the microhardness is 3600-3700 MPa. Below, as it deepens, there is a light-colored zone up to 90 microns thick, the microhardness of which is about 3200 MPa. Even lower microhardness gradually decreases and at a depth of ~ 280 μm corresponds to the microhardness of the base.

As a result of electron microscopic studies, the structure of the combined coating formed on steel 12Kh18N10T was obtained, consisting of a T15K6 hard alloy and a grease, including MPM and VK6 carbide mixture, FIG. 9.

In FIG. 9 clearly visible 4 zones. On the surface there is a lighter zone of variable thickness (160-180 microns), consisting of MPM and VK6 carbide mixture. Below is a zone of a darker color, the thickness of which reaches 120 μm, formed as a result of the phased deposition of T15K6 hard alloy on a substrate of 12Kh18N10T steel. Below is a zone of an even darker color with a thickness of 20-30 microns, which is probably a transition or diffusion zone. And even lower is the zone consisting of base material.

The chemical composition of the resulting coatings was investigated. In FIG. 10 shows the distribution of elements along the depth of the layer. The results of X-ray microspectral analysis indicate an increased content of tungsten and titanium in the surface layer (up to 240 μm deep), the increase in the number of which is explained by the entry of these elements into the composition of carbide electrodes. At the same site, a reduced content of iron, chromium and nickel - the main elements of the steel substrate. The maximum amount of carbon and oxygen on the surface, as it deepens, gradually decreases to their amount in the base metal at a depth of 240 and 170 microns, respectively. Microstructural analysis of the obtained coatings showed that in all laser treatment modes the surface layer consists of 3 zones: 1 - near-surface “dark” layer, 2 - “light” layer and 3 - base metal, FIG. eleven; 13; 15; 17; nineteen; 20.

The thickness and microhardness of the obtained layers is determined by the laser processing parameters.

The microstructure of the coatings obtained according to regime 1, FIG. 11, 12, is characterized by the presence of a thin and not uniform in thickness “dark” layer (up to 10 μm) with a continuity of about 65%, which has the highest microhardness of 6110 MPa. The second layer is “light”, has a low etchability in aqua regia and has a hardness of up to 2650 MPa, its average thickness is about 100 microns, and the continuity is 100%. Metallographic analysis showed that the transition layer between the “light” layer and the base metal is not expressed, and the microhardness of the formed “light” layer differs little from the hardness of the base metal, which is apparently due to the use of “soft” laser processing modes (Table . one).

As a result of applying the processing according to mode 2, FIG. 13, 14, the thicknesses and microhardness of the formed zones in the coating increase (Table 2): the outer “dark” layer with a thickness of up to 40 microns has the highest hardness of up to 7200 MPa; The 2nd “light” layer has a thickness of about 130 microns and a hardness of ~ 3200-4500 MPa. The obtained layers in these processing modes are characterized by increased continuity of up to 100% and uniformity in structure and thickness.

The parameters of the surface layer of the sample in FIG. four.

The increase in thickness and microhardness of the hardened layer during processing according to mode 2 (Table 2) can be explained by a decrease in the frequency from 100 to 50 Hz.

When processing in mode 3, FIG. 15, 16, the outer “dark” layer with a thickness of up to 50 μm has the highest hardness of up to 8900 MPa; The 2nd layer has a thickness of about 190 microns, in this zone the microhardness is maximum at the border with the first zone (about 6500 MPa) and decreases as it deepens.

Studies have shown that with increasing laser pulse from 0,3⋅10 ^-3 to 1⋅10 ^-3 (Tab. 1) on the modes 2 and 3, respectively, and the thickness of the hardened layer increases the microhardness (Tab. 2).

The results of metallographic studies of coatings obtained in mode 4, FIG. 17, 18, showed that in the coating a “dark” layer having a thickness of up to 100 μm is characterized by a maximum microhardness of up to 9250 MPa and a 100% continuity. With an increase in voltage from 500 to 550 V in modes 3 and 4, respectively, the thickness and microhardness of the obtained layers increase. So, the “light” layer has a microhardness of 6000-7250 MPa, which decreases as it deepens. The thickness of the "light" layer is about 230 microns.

The microstructure of the layer obtained in mode 5, FIG. 19, 20, 21, as in other processing modes, is characterized by the presence of 3 zones: the outer “dark” layer (the longest up to 420 microns) has a characteristic porous structure (Fig. 19), its hardness varies between 6100-7300 MPa, while there are separate sections with a hardness of up to 10 GPa (Fig. 20, 21). The second layer is “light” up to 260 microns, poorly etched with reagent (aqua regia), has a maximum hardness at the border with the first layer of 7400 MPa and gradually decreases to the hardness of the base metal in zone 3.

The maximum microhardness and thickness of the “dark” and “light” layers for each laser treatment mode are presented, respectively, in FIG. 22, 23, 24, 25.

Claims (4)

1. The method of restoring worn surfaces of machine parts from stainless steel, in particular 12X18H10T, including applying to the worn surface of a part of a coating with electroerosive alloying (EEL) with a T15K6 hard alloy electrode using a discharge energy initially of Wp = 0.55 J, and then Wp = 0 , 90 J, applying to the obtained surface a reinforced metal-polymer material (MPM), ensuring its polymerization and final machining, characterized in that prior to polymerization, the MPM is reinforced with metal powder of hard alloy VK8, and after polymerization of a layer of reinforced MPM before its final machining, laser processing is performed. 2. The method according to p. 1, characterized in that when reinforcing a metal powder of VK8 hard alloy, 5-7% of the total amount of added metal powder is added to the MPM in portions, after each portion the resulting mixture is thoroughly mixed, and before application to the EEL formed coating the concentration of powder in the mixture was adjusted to about 60%. 3. The method according to p. 1, characterized in that the laser treatment of the layer of polymerized reinforced MPM is performed after it has been dried for 24 hours. 4. The method of claim. 3, characterized in that the laser treatment is performed under applying a sample of 120 mm / min, the laser source voltage of 500-550 V, the pulse laser 0,3⋅10 -1⋅10 ^{-3 -3} s and the pulse repetition rate of 50-100 Hz, while the thickness and microhardness of the treated layer is increased by increasing the voltage of the laser source from 500 to 550 V, increasing the laser pulse from 0.3⋅10 ^-3 to 1⋅10 ^-3 s and reducing pulse repetition rates from 100 to 50 Hz.

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