SU1721103A1 - Process for thermal and chemical treatment of precision parts - Google Patents

Abstract

The invention relates to the chemical and heat treatment of steel products and can be used to restore and strengthen precision parts, mainly plungers of diesel fuel engines. The aim of the invention is to reduce deformation and fatigue wear. The plunger is cleaned, a slurry of metal powder and liquid glass is applied to its lower part cross-pt, dried, placed in a borating melt consisting of borate slag heated to 950 ° C, and kept there for 10 minutes the upper part of the plunger is cooled with circulating water. At the end of boring, the plunger is cooled and subjected to low tempering combined with sulphurisation for at least 60 minutes. The application of the method allows to reduce the deformation and fatigue wear of precision parts. 1 hp f-ly, 3 ill., 2 tab. ate G

Description

The invention relates to the chemical heat treatment of steel products and can be used to restore and strengthen precision parts, preferably plungers of diesel fuel pumps.

The closest to the present invention is the method of chemical heat treatment of precision parts — boronation.

However, boring precision parts in a known manner is associated with significant difficulties. Carrying out the process at a high temperature of the melt leads to deformation of the parts, subsequent heat treatment does not relieve completely residual stresses and leads to the appearance of microcracks on the surface, which leads to increased fatigue wear on the areas of the plungers operating under shock cyclic loads.

The aim of the invention is to reduce deformation and fatigue wear during the chemical-heat treatment of precision parts.

According to the method of chemical heat treatment, including cleaning the surface, heating in boron-containing melt to 950 ° C, holding it. subsequent heat treatment — normalization and isothermal quenching, before being heated in the melt, the lower region of the cross-plunger is suspended from metal powder and water glass and dried, after which it is placed in the melt for 10 minutes, while the upper region of the plunger is cooled, subsequent heat treatment, low tempering is carried out simultaneously with sulfoborination for at least 60 minutes. In addition, as an extension

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about with

melt using synthetic borate slag.

Figure 1 shows the implementation of the proposed method; 2 and 3 are graphs explaining the method.

The method is carried out as follows.

A slurry layer 1 is applied to the lower area of the plunger, a cross made of dirt, 70% of FeCr powder, 30% of bronze powder and 6% of the volume of metal powder of liquid sodium glass with a thickness of 1.4 mm (figure 1). and placed in a drying cabinet, where it is heated to 180 ° C for 45 minutes. After that, the lower region 2 of the plunger is placed in a bath of molten synthetic borate slag, having 950 ° C, and maintained for 10 minutes, the upper region 3 of the plunger is cooled in the grip.

The cooling is carried out with circulating water of 20 ° C, which is directed under a pressure of 2 kg / cm2 into a gripper made of fused mullite (the temperature of the onset of deformation under a load of 2 kg / cm2 1700 ° C).

The heating is carried out to a temperature exceeding the solidus temperature of the applied layer and below the solidus temperature of the material of the precision parts to 950 ° C. The use of synthetic borate slag as a melt, which in combination with sodium liquid glass is actively involved in the spraying of metal powders and the constituent elements of steel, makes it possible to form a wear-resistant layer on a metal substrate with low porosity and high bond strength with the substrate.

 The hardness of the obtained layer according to Vikkers (HV) is measured every 1.5 minutes of melt aging (after cooling in air to 20 ° C). As can be seen from the obtained results (Fig. 2), already after 10 minutes a layer with a hardness of 900 ... 930 HV is formed. Further melt aging does not affect the change in hardness (Fig. 2).

After 10 minutes of melt aging, the plunger is removed and held in air up to 145 ... 150 ° C. Then the slag is separated and the subsequent heat treatment (low tempering) is carried out with simultaneous hardening, by sulfobriting in a salt bath of the following composition, wt%: water 40 ... 42; caustic soda 42 ... 44; sodium sulphide 1.5 ... 2.5; sodium hydrochloric acid 1 ... 2; borax 6.5 ... 7.5; boric acid 5 ... 6 and maintained at 150 ° C for at least 60 minutes.

The tests carried out showed that the complete saturation of the surface layers

samples by chemical compounds with the formation of a uniform diffusion layer up to 100 µm in depth with a microhardness of 14000 ... 14500 MPa occurs after

50 ... 60 min exposure (fig.Z). Further exposure in the salt solution does not affect the microhardness of the resulting diffusion layer.

The process of sulfoborizing, combined with a low tempering, makes it possible to remove residual surface stresses and eliminate microcracks in the area of high-temperature heating, to obtain a layer that reduces the moment of friction and the intensity of wear of precision parts.

As is known, plunger pairs have in their mating a small gap (0.6 ... 2 μm), which causes their high sensitivity to diesel fuel contamination by solid particles, which cause increased abrasive wear of plunger parts and their quick exit from build The above composition of the plunger pairs sulfoboarding bath allows the floor5 to form a uniform diffusion layer. The resulting hardness is 1.2 ... 1.3 times higher than the hardness of the primary abrasive - quartz, which wears the upper part (Fig. 1) of the plunger, thereby increasing the wear resistance of the plunger pairs under the conditions of abrasive wear.

However, an analysis of the reliability of distribution fuel pumps of the type ND / 21, ND / 22 showed that the increased cyclical operation of the plunger drive parts (the camshaft and its connection with the leading bevel gear, the lower spring plate of the plunger pusher, the intermediate gear bracket assembly,

0 plunger pusher assembly, cross-pc plunger type ND), higher alternating dynamic loads acting in these parts as compared to multi-plunger regular pumps,

5 leads to increased wear and deterioration of the pump fuel delivery characteristics. Worn parts of the drive can lead to a decrease in the active stroke of the plunger by 1.5 ... 2.0 mm, which causes a reduction in feed

0 fuel at start-up mode and pump life by 25 ... 30%, increase in feed start angle on the camshaft by 3.5 ... 4.0 ° and delay in supplying diesel to the cylinders by 7 ... 8 degrees in the corner turning the knee 5 of the shaft, reducing diesel power by 5% and increasing the specific fuel consumption by more than 10%.

Thus, the proposed combined hardening method allows to increase the wear resistance not only of the surface of the upper part of the plunger (abrasive wear), but also of the lower area of the plunger of the ND type (fatigue wear).

Example 1. To determine the change in the size and shape of parts, typical samples were made of steel 25X5MA, imitating plunger of distribution type ND 0 9.0 mm; 78.0 mm. The surface roughness of the samples before testing is Rd 0.040, the non-roundness is no more than 0.2 microns. non-cylindrical - no more than 0.6 microns.

Samples, thoroughly cleaned of dirt, are placed in a melt of technical boron carbide with a grain size of 120 ... 200 µm (No. 8-16) having a temperature of 950 ° C, and kept for 3.5 hours. Technical fluoride aluminum according to GOST is used as an activator . The parts are then subjected to normalization and isothermal hardening from 850 ° C in a bath with a temperature of 350 ° C and maintained there for 1.5 hours (the boronization process).

Other samples are treated as follows. A suspension of 70% of FeCr powder (Ф0650 GOST 4757-70), 30% of bronze powder (Br ОФ10-1 ОСТ 1.90054-72) and 6% of the volume of metallic powder of liquid sodium glass (GOST 13078-81 ). Then placed in a drying oven (grade LP-306 of the company Labar MIM), where it is kept for 45 minutes at 180 ° C. After that, a part of the sample, the end of which is coated with a suspension, is placed 20 mm in a bath of molten synthetic borate slag (AN-Ш1 TU 21 SSR 5-77 basicity, B 0.35), having a temperature of 950 ° C, and held for 10 minutes. At the same time, the upper part of the sample is cooled with circulating water of 20 ° C, directed under a pressure of 2 kg / cm2 into the grip.

The hardness of the resulting layer in the melt is measured every 1.5 minutes of exposure. As can be seen from the results (Fig. 2), already after the tenth minute a layer 900 ... 930 HV is formed. Further melt aging does not affect the change in hardness. At the end of this heat treatment, the samples are kept in air up to 145 ... 150 ° C and after slag separation is placed for subsequent heat treatment (low tempering) in a salt bath of the following composition, wt.%: Water 40 ... 42; caustic soda 42 ... 44; granular sodium 1.5 ... 2.5; sodium hydrochloric acid 1 ... 2; Borax 6.5 ... 7.5; boric acid 5 ... 6.

The process is carried out at 150 ° C for 60 minutes. Tests have shown that the full saturation of the surface layers of the samples during sulfoboring by chemical compounds with the formation of a uniform diffusion layer up to 100 5 microns in depth with a microhardness of 14,000 ... 14,500 MPa occurs after 50 .., 60 minutes exposure (Fig. 3). Further exposure in the salt solution does not affect the microhardness of the resulting diffusion layer.

0 Change geometric parameters

Before and after processing, they are monitored with a VE201 model profilograph-profilmeter of the Caliber plant, with an instrument

.. Taliserf-4, the device company Taylor

5 Hobson.

The test results are presented in Table 1, where the data on the changes in the geometric parameters of steel samples before and after processing are presented.

0 As can be seen from the obtained data, the geometrical parameters of the samples processed by the proposed method are practically unchanged, while the non-cylindrical deviations of the cylinders are 18..26 µm, the non-roundness is 0.7 ... 1.0 µm.

EXAMPLE 2 The determination of residual stresses in the surface layers is carried out by measuring the deformation of a rod with a diameter of 9.0 mm and a length of 78.0 mm, resulting from the unilateral removal of the surface layers of metals by electrolytic etching.

The strain measurement is performed

5 strain gauge resistance sensors FKP-20-200, glued directly onto the test sample along its axis. The semi-annular surface of the centerline of the pasted sensor is protected

0 from pickling. Etching is performed in an electrolyte of 50 g of NaCI and 100 g of ZnSOs per f l of distilled water at a current density of 5 A / dm. Know the etching rate and instrument readings, i.e. thickness of the layer

5 The magnitude of the deformation e, the residual stresses are calculated by the formula

a ° ST 2 ()., A4 1G (

P & | (50-T (

0 here + E / Aozg l -,

where Oost is residual stresses;

E is the modulus of normal elasticity of FeB taken by S-IO4 kg / mm2;

r is the radius of the rod; di is the total thickness of the etched layer;

Yep offset the center of gravity of the section from the axis after removing the layer;

five

 - moment of energy of the rod after poisoning a layer 5 | thick;

1 (5 |) is the distance from the center of gravity to the lower fiber after poisoning a layer of thickness d;

RF is the section area after the layer has been etched with thickness d;

And - current density; e - rod deformation.

Derivatives are calculated based on experimental data. The test is subjected to borated and samples treated with the proposed chemical-thermal method.

Table 2 presents the results of the determination of residual stresses and bending fatigue tests with the rotation of steel specimens.

As can be seen, the residual voltages of the samples that underwent low tempering by sulfonation. 2.0 ... 2.2 times less than that of borated ones, which have subsequent normalization and isothermal hardening.

In parallel with studies to determine the residual stresses, wear-wear tests of cylindrical specimens of steel SHKh15 on an NU machine (3000 rpm) are carried out, the loading of which is carried out according to the scheme of pure bending during rotation. The endurance limit of the samples treated by the proposed method based on the first 107 loading cycles is 130 MPa. Upon repeated loading, boron specimens that have undergone 104 loading cycles under a stress of 280 MPa, after electropolishing the surface, fatigue cracks with a length (along the surface of the specimen) of 7 ... 9 µm and a depth of 10 .. 24 µm were detected. The stress did not change on the sulphate-coated coating and fatigue cracks were absent (Table 2).

Example 3. In order to determine the moment of friction and the maximum load of the setting, tests were performed on the friction machine SMC-2 according to the disk-drive scheme. The material for the samples is steel 25X5MA. Investigate borated and sulboboric surface diffusion layers. The test was carried out for 6 hours at a specific pressure of 1.5 MPa, a disk rotation frequency of 1000 rpm and a relative sliding speed of 2.618 m / s. The lubricating fluid is DL (GOST 308-80) diesel fuel with a viscosity of 6 cSt. which is served in the friction zone at 30 ... 40 drops in one minute.

The moment of training was recorded in the initial period after 3 ... 5 minutes, then after 15 minutes and then after 30 minutes of work. As a result of the test it was found

that the moment of friction of sulfoborized samples is 1.6 times less than the moment of training of fins and was established after 0.5., .6 hours after the start of the test. The test procedure for the specimens envisaged the establishment of a maximum load (at which the rubbing surfaces set. By a spasmodic increase in the magnitude of the moment of friction, its dependence on the setting load was revealed.

Tests have shown that the setting of borated specimens occurs much faster with a load of 0.6 kN, with sulfoborized ones with a load of 1.4 kN.

0 No deformation and microcracks, low residual stresses and a low friction moment, a high limit load of the friction surfaces setting is the most reliable parameters that show the resistance, processed by the proposed method, to fatigue wear.

These data are confirmed by the test certificates attached to the previous report.

0 for vke.

X-ray diffraction and metallographic analyzes of the diffusion surface layer were carried out after sulfoborurization.

5 X-ray structural studies have established that the layer obtained in the process of sulfoboring is composed of iron sulphides, borides, borates and intermetallic compounds of FeB, which have high

0 physico-mechanical properties.

By the results of metallographic analysis and layer-by-layer measurement of the microhardness of the sulfoborized layer, it was found that the coating has

5 surfaces the sulfide layer is 0.2 ... 0.5 μm with a microhardness of 3000 MPa and a sublayer up to 100 μm with a microhardness of 14000 ... 14500 MPa. The resulting diffusion layer at the expense of sulphides reduces the coefficient of friction, and at the expense of a sublayer of high hardness (1.2 ... 1.4 times higher than serial plungers) - increases the wear resistance of precision parts under conditions of hydroabrasive wear.

5 Using the proposed method, compared with the known, reduces the deformation of the surface layers due to non-durable local heating and preservation of the original geometrical parameters, which eliminates the subsequent machining of the friction surfaces, obtaining the necessary layer on the cross-punk plunger surface to restore worn areas, the possibility of friction surfaces without microcracks and residual stresses, with low friction coefficient and high setting load, h about significantly reduces fatigue wear precision parts, working in conditions of shock loads and cyclic-hydro-wear.

Claims (2)

1. The method of chemical-heat treatment of precision parts, mainly plungers, including surface cleaning, heating in a boron-containing melt, up to 950 ° C, holding in it and cooling, about that. that, in order to reduce deformation and fatigue wear, before heating in the melt, a suspension of metal powder and water glass is applied cross-pt to the lower region of the plunger, dried, placed in the melt and 0 is kept in it for 10 minutes, while the upper part of the plunger is cooled with circulating water, and after cooling, the plunger is subjected to low tempering combined with sulfoboring for at least 60 minutes. 2. The method according to claim 1. This is due to the fact that borate slag is used as the boron-containing melt. Table Rough toast, micron: Boiled7 (known) 140 ... 150 10 Processed by the proposed method 64. ..65 Ю7 Table 2 ten ten 260 ... 270 270 ... 280 7 ... 9 10 ... 24 130 ... 135 135 ... - SSS / / SSSSS / S // with about “0 CO si CN gy Cccccccccccccccccccc h-P1 J . & YU AND s about " An 3D (, 5SO Cry t min FIG. SO