Steel 38KhMYuA Research Articles

ДОСЛІДЖЕННЯ ВПЛИВУ ПОКРИТТІВ І ТЕХНОЛОГІЧНИХ МЕТОДІВ ВИГОТОВЛЕННЯ НАПРЯМНИХ ЕЛЕМЕНТІВ НА ЇХ ЗНОСОСТІЙКІСТЬ

The matter of the experimental studies of the effect of coatings and technological methods of manufacturing guide elements of universal prefabricated readjustable tooling on their wear resistance are presented. The coatings investigated were made of VK15 carbide powder, which were applied by detonation spraying, and a titanium nitride-based coating produced by condensation with ion bombardment, as well as the surface hardening of guide elements by diamond burnishing for various steels: 20V, 12KhN3A, 40Kh, 38KhMYuA-B and others.During the process of diamond smoothing the roughness improves by 2 - 3 classes and the very nature of the roughness changes: a surface microrelief is created with rounded peaks and valleys instead of microroughness with sharp peaks and valleys, which are characteristic of surfaces after grinding. In this case the bearing surface of the samples increases essentially, and their running-in is accelerated. According to the results of tests under a load of 50, 75 and 100 kgf, a graph of the dependence of wear on the specific pressure was built and it was found that the wear of samples after burnishing decreases by 25 ... 40% compared to polished and at a load of 20 kgf/cm, respectively, is for steel 20 ... 2.7 and 1.9 μm, for steel 12XN3A – 2.3 and 1.6 μm, for steel 40X – 1.8 and 1.3 μm and for steel 38XMYUA – 1.4 and 0.8 μm.With increasing the load the wear of the ground specimens increases sharply, and for the flattened specimens this process is much slower. Based on the test results, graphs of the wear rate were plotted depending on the test duration, as well as for wear in relation to the number of cycles. According to the test results, it was found that steel 38KhMYuA has less wear, which is associated with its high hardness and insignificant tendency to metal seizure. Based on the research results, it was found that different methods of processing parts (previous) grinding and diamond burnishing have different wear. It has been found that diamond burnishing is a very effective surface hardening process.As a result of the tests carried out, it was found that the best performance in testing for wear resistance obtained for a column with TiN coating, the thickness of which does not exceed 0.1 μm, is 5 - 6 times less than the wear resistance of columns with a hard-alloy coating. For the system of directly changeable dies, a pair is recommended, which includes a guide column with a detonation coating VK15 and a holder (sleeve) with a CIB coating based on TiN, since these coatings showed high performance properties and had practically no wear.

TECHNOLOGICAL PASSPORT STUDY PISTON AND CONNECTING ROD BARE MATERIAL AXIAL ROTARY PISTON PUMP

A technological passport of the alloy steel material has been formed, from which a piston-connecting rod pair of an axial-rotor piston pump is made in the form of functions: flow curve, plasticity diagram, Bauschinger curve, calibration graph. Using the approximation of the neck contour by the Gaussian function at any moment of deformation of a cylindrical specimen in the supercritical region, the main parameters used in engineering calculations are related: the minimum diameter of the specimen, the current diameter of the specimen with a given coordinate, the relative (absolute) elongation and contraction with the parameters referred to the moment of rupture sample. In addition, the elongation and contraction of the sample after fracture are unambiguously associated. The approximation avoids the inconvenient and relatively expensive video filming for studying the history of deformation. It is shown that the effect of heat treatment on the mechanical properties of these steels is not the same for different stress state schemes. The tensile strengths of these steels are close as delivered. The plasticity characteristics of steel 30Kh3MFA exceed the plasticity of steel 38Kh2MYuA by 1.5 times. The flow curves of the steels under consideration have the following tendency: so the coefficient of approximation of the flow curve for 38Kh2MYuA steel in the delivery state exceeds its value in relation to steel 30Kh3MFA by 1.23 times. After heat treatment of these steels, the value of the approximation coefficient increases: for steel 38Kh2MYuA by 1.11 times, for steel 30Kh3MFA by 1.46 times. The results obtained make it possible to control the mechanics of the technological operation of rolling the piston-connecting rod pair and create a process control mechanism in order to prevent rejects during the rolling process, which manifests itself in the form of going beyond the tolerance field for the axial clearance of the piston-connecting rod pair, as well as destruction during rolling of the inner part of the piston.

Improvement of Compressor Seal Assembly Elements. Part 2

A new more efficient technology for manufacturing protective sleeves is proposed, whose surface layer is subjected to integrated strengthening technology: ion nitriding, polishing, carburizing using electro-erosion alloying, and nonabrasive ultrasonic finishing. The protective sleeve material may be steel 38KhMYuA or 40KhN2MA.

Effect of heating conditions in nitriding on the structure and wear resistance of surface layers of steel 38Kh2MYuA

The structure and properties of nitrided layer on steel 38Kh2MYuA are studied as a function of the mode of heating to the nitriding temperature. The heating conditions promoting high wear resistance of the nitrided layer are determined.

Ion nitriding in glow discharge with hollow cathode effect

The process of ion nitriding in the plasma of glow discharge under the conditions of occurrence of hollow cathode effect (HCE) is studied. The action of the HCE on the parameters of the glow discharge and on the structure and distribution of microhardness over the thickness of nitrided layers on steel 38KhMYuA and on titanium alloy VT22 is determined. Nitriding in glow discharge without HCE is performed for comparison.

Structure and Wear Resistance of Nitrided Steel

The effect of the temperature of preliminary tempering and gas nitriding on the wear resistance and structure of surface layers of steel 38Kh2MYuA is investigated. Triboengineering and structural characteristics of nitrided layer including a layer with virtual absence of wear are obtained. Ways for optimizing nitriding modes are outlined.

Use of Double Thermochemical Treatment in the Production of Tools from Structural Steels

It is shown that double thermochemical treatment (nitrocarburizing and nitriding) with subsequent heat treatment can be used for the production of cutting tools from alloy structural steels instead of tool steels. A process for treating milling cutters from steel 38Kh2MYuA and blades from steel 0KhN3MA is suggested.

Kinetics of formation of a diffusion layer on steel 38Kh2MYuA in gas-cyclic nitriding

Results of a study of the effect of the cycle duration and the degree of dissociation of ammonia on the structure and properties of a nitrided layer on steel 38Kh2MYuA formed at a temperature of 570°C are presented.

Strengthening steel 38Kh2MYuA by nitriding in various media

At the present time critical parts of various machines and equipment operating under conditions of wear under cyclic loads are often produced from low-alloy steel 38Kh2MYuA. Its operating properties are usually improved by surface strengthening by the method of nitriding. A wide range of nitrogen-saturating atmospheres has been developed for this purpose, with each diffusion medium characterized by special process properties. The present paper is an analysis of data on nitriding structural steel 38Kh2MYuA in gas, liquid, ionic, vacuum, and powder nitrogen-bearing media. Recommendations are given for practical use of nitriding of the studied steel so as to obtain the requisite operating properties.

Surface hardening of steels by alloying with laser heating and subsequent chemical heat treatment

The necessity of providing a high set of operating properties has stimulated the development of combined technologies of surface hardening. A combination of laser alloying of low-carbon steels by nitride-forming elements (V, Cr, Mo, Al) with subsequent chemical heat treatment seems promising in this respect. Such a combined treatment provides a favorable distribution of residual stresses, elevates considerably the microhardness of the strengthened layers, and increases the wear resistance by a factor of 1.5–3 compared to nitrided nitralloys like steel 38Kh2MYuA.

Control of the phase composition and nitrogen content in the nitride layer in the nitriding of the steel 38Kh2MYuA

It is known that in order to obtain a high-hardness, wear- and corrosion-resistant article a nitrided layer of nitride e(e+γ′)-phases should be formed on its surface. However, in some cases, for example, in nitriding high-speed die steels and steel 38Kh2MYuA, the formation of brittle nitride surface layers should be eliminated and only a zone of internal nitriding (a+ γ′ + MN) should be formed in order to provide the requisite hardness and wear resistance. The article concerns preparation of nitrided layers with different compositions on the widely used 38Kh2MYuA nitralloy.

Structure and properties of coatings built up by CO2-laser radiation

1. Lowering the content of chromium and carbon in powder materials of the system Ni−Cr−B−Si reduces the proneness to cracking of built-up coatings. 2. Preliminary heating of the specimen (part) to 100–150°C eliminates almost completely the proneness to cracking of built-up coatings when the facing materials are nickel base powders of the self-fluxing class. 3. In regard to corrosion resistance built-up coatings are not inferior to galvanized chromium coatings and are better than alloy steel 38KhMYuA. Such coatings have long life even when there are cracks on the surface. 4. Built-up coatings have good seizing resistance both at room temperature and at elevated temperatures, and their wear resistance is one order of magnitude better than the wear resistance of steel 45 heat-treated to HRC 51–53.

Application of steel 40Kh surface hardened by high-frequency currents in the production of gate valve parts

Bench tests were performed to determine the change in roughness, planeness, and hardness of the sealing surfaces of parts of gate valves made with steel 40Kh surface-hardened by high-frequency currents (HFC). Most parts of the gate valves for oil wells are now made of steel 38Kh2MYuA containing molybdenum. It was of interest to conduct tests to find another steel (40Kh) with less precious alloying elements and to increase the hardness of the sealing surfaces. The tests showed that steel 40Kh with HFC surface hardening may be recommended for gate parts of straight-through gate valves with specific contact pressure of up to 70 MPa. The torque for controlling the gate must be 0.8-1kN. Tests were also conducted on an experimental batch of Christmas trees and tubing heads; those results are presented.

Nature of the high hardness and brittleness of the nitrided case on steel 38Kh2MYuA

Nature of the high hardness and brittleness of the nitrided case on steel 38Kh2MYuA

Nitriding of low-carbon martensitic stainless steels 03Kh11N10M2T and 03Kh12N10MT

1. The nitrided case on steels 03Kh11N10M2T and 03Kh12N10MT, from the surface to 50–70% of the total case depth, has high corrosion resistance in a humid atmosphere and in salt spray. 2. Tempering before nitriding, which ensures a good combination of mechanical properties of the core and the case and high stability of the structure and the dimensions during nitriding and operation, should be conducted at 580° for 10h or 640° for 4 h+580° for 10 h (steel 03Kh11N10M2T) and at 570° for 6h (steel 03Kh 12N10MT). 3. The nitrided case on steels 03Kh11N10M2T and 03Kh12N10MT does not fracture when subjected to tensile stresses as high as the proof stress of the core. 4. Retained austenite formed in steels 03Kh11N10M2T and 03Kh12N10MT during tempering and nitriding is stable at negative temperatures as low as -196° and also when subjected to tensile stress as high as the proof stress at temperatures as low as -196°. 5. After nitriding, σb=100–120 kgf/mm2 for steel 03Kh11N10M2T; with a case depth of 0.20–0.25 mm, the ductility and toughness are superior to those of widely used nitriding steels 30Kh3VA and 38KhMYuA with a case depth of 0.45 mm and it is recommended for nitrided machine parts operating at temperatures from-70 to +450°. 6. Nitrided stainless steel 03Kh12N10MT has high toughness and ductility in combination with high strength at cryogenic temperatures, and it can be recommended for nitrided machine parts operating at temperatures from -253 to +350°.

High-strength rapid-nitriding steels

1. High-strength rapid-nitriding steels containing Al, V, Ti, Mo, Cr, and Ni were developed. A hardness of H50=1000–1500 can be obtained after nitriding of these steels at 660°. The nitriding time is five to eight times shorter than for steel 38KhMYuA to obtain the same case depth and hardness. 2. With 0.3% Mo and as much as 0.1% C the hardness of the case increases, and also the ductility and toughness. 3. Alloying with vanadium substantially increases the hardness and case depth. The change in the mechanical properties depends on the ratio of vanadium to carbon. The hardness is highest with V/C=10–20. Steel 10KhN4Yu4FA is recommended for machine parts operating under conditions of intensive wear without substantial load, and steel 30KhN4Yu4FA (V/C=2) for machine parts operating under heavy load. 4. Alloying of these steels with titanium is inexpedient, since it lowers the toughness of the steel and induces cracking of the nitrided case. 5. Lowering the aluminum content to 1–2% in steel with 2% V increases the toughness to 5.4 kg-m/cm2 and increases the case depth without substantially reducing the hardness.

Brittleness of the nitrided case on steel 38KhMYuA

1. The brittleness of the nitrided case on steel 38KhMYuA depends to a considerable extent on the grain size. Raising the quenching temperature above the specified is undesirable, since it induces grain growth and increases the brittleness of the case. 2. Nitriding with CCl4 reduces decarburizing and the hydrogen content of the steel, somewhat increasing the microhardness and the brittleness of the surface layers, which may be due to a higher nitrogen content. 3. At a depth of 0.15 mm the brittleness of the case disappears after nitriding with or without CCl4.

Low-temperature carbonitriding of gear wheels

1. We investigated and introduced in production a process of low-temperature carbonitriding for structural steels in triethanolamine without preliminary pyrolysis. 2. The microhardness of the ɛ layer in different steels was HV20 800–950, with satisfactory brittleness (group 1). 3. The best results were obtained with steels 20Kh, 18KhGT, 12KhN3A, 20, and 38KhMYuA. 4. The optima parameters of the process are as follows: 600°, 6–7 h, 40–70 mm water column, and 60–80 drops/min of triethanolamine for alloy steels; 600° and 6 h for carbon and nickel steels.

The fine structure of nitrided steels

1. The structures formed in the process of nitriding are similar to those observed in aging alloys (Cu−Be and Ni−Be alloys, for example) during decomposition of supersaturated solid solutions. 2. It was found that the nitride phase precipitated in binary Fe−Al, Fe−Cr, and Fe−Mo alloys and steels 40Kh and 38KhMYuA have a B1 structure (NaCl type). 3. The high strength of the nitrided case on steel 38KhMYuA is due to a considerable extent to distortion of the matrix (α phase) resulting from the formation of finely dispersed nitrides completely or partially coherent with the matrix. The maximum hardness is reached in the initial stage of nitride formation when then thin (single layer of nitrogen atoms) lamellar nuclei are completely coherent with the matrix. 4. The high hardness of the nitride case is due mainly to aluminum. The addition of chromium and molybdenum to steel 38KhMYuA makes it possible to obtain (at a sufficiently high nitriding temperature) nitrides with a structure corresponding to the early stages of their formation, which favors a fairly large case depth and high hardness.

The effect of ionic nitriding on the fatigue limit of steel 38KhMYuA

The effect of ionic nitriding on the fatigue limit of steel 38KhMYuA