Metallographic Methods Research Articles

Application of an integrated method to improve the quality of manufacturing parts of electronic warfare devices

Objectives. The development of technological methods with the purpose of increasing the structural strength of defense engineering products can be carried out by creating new methods for obtaining and processing parts or improving traditional methods based on an integrated (synergistic) approach. The article presents a complex method for surface treatment of parts and assessment of the hardness and surface roughness of the initial workpiece from alloys of the Al–Mg system to improve the quality of manufacturing the module cases of the MSP-418K product related to electronic warfare devices.Methods. This approach consists in the vision of a metallic material as a system subjected to a chain of technological impacts in the process of chemical, thermodynamic, and mechanical interaction of its components. The workpieces were obtained by metal pressure treatment according to various schemes and temperature conditions Then they were processed with a blade tool using a dynamometer. The resulting cut was examined using a metallographic method along the entire end face from the outer surface to the center of the sample of workpieces.Results. Experiments were carried out for the case of Al–Mg alloys. It made it possible to reveal the relationship between the parameters of the change in the structure of the material being processed and the stability of the cutting process, as well as the quality of the surface during finishing turning.Conclusions. The proposed technological solutions based on a synergistic approach provided a balanced improvement in material parameters by eliminating the shortcomings of the original semi-finished product. The obtained experimental data allowed concluding the deformation of workpieces according to complex schemes at low temperature has a beneficial effect on the machinability of the metal material, ordering the structure and improving the quality of the surface of the parts. Using a synergistic approach, it became possible to correct the poor technological heredity of material properties obtained in previous operations: the surface quality of the workpieces due to the continuity of the processed material and the strength properties of parts for critical and especially critical purposes were improved. The existing technological process for manufacturing the “petal” part was changed in practice using an integrated method, which made it possible to improve its technological and technical characteristics.

Automatic analysis of nonmetallic inclusions in steel using electron microscope with energy dispersive microprobe with

Clean steel non-metallic inclusions have a significant effect on the physic and mechanical as well as technological properties of the metal and consequently on the quality of the final product. There are many methods for detecting and evaluating nonmetallic inclusions. Traditional methods for assessing the contamination of metal with microinclusions are metallographic methods, which are divided into methods for comparing the contamination of the section with inclusions with reference scales and counting methods. The classification of inclusions by traditional methods on a polished section is based on morphological features: shape, color, aspect ratio, etc. In addition to traditional optical microscopy, an electron microscope is used for studies that are more detailed. Equipping an electron microscope with an attachment for energy-dispersive microanalysis allows classifying nonmetallic inclusions by chemical classes. As a result of the implementation of a set of organizational and technical measures, BMZ, the management company of BMK Holding, installed and put into operation research equipment in December 2020 – a scanning electron microscope with an energy-dispersive microanalyzer (SEM with EMF). Thanks to the software module that the microanalyzer is equipped with, the possibility of automatic analysis of non-metallic inclusions is implemented. The software settings include the search for non-metallic inclusions and their classification according to widely used international standards. The flexible configuration of the software allows you to create models for separating inclusions into different user classes.

Austenite Grain Growth Law of High-strength Steel for Offshore Engineering

The metallographic analysis method is used to study the original austenite grain change law of Nb-containing high-strength ship steel. Adding Nb to the experimental steel will refine the grains to a certain extent. Different Nb content, the corresponding grain size change trend is different. Under the experimental heating environment of 850°C~1150°C, the grains of the two experimental steels have different degrees of coarsening at different heating temperatures. Compared with the low-C and high-Nb steel (EH36) with the high-C and low-Nb steel (AH36), the former can not only control the austenite grain growth well at lower temperature, but also has a strong inhibitory effect in a higher temperature environment. Based on the experimental data, the austenite grain growth kinetic model of the two experimental steels at the heating temperature of 850°C~1150°C is obtained.

Studying on the Internal Quality of Steel at Various Stages of Production: Slab-Rolled Metal

In this work, the characteristics of the cast structure formed under various conditions of slab casting and the micro-structure of hot-rolled sheets made from them are studied by a complex of chemical and metal-graphic analysis methods. This article presents the results on cast structure's dispersion studying of continuously cast slab that depend on the casting speed as well as hot rolled steel's the microstructure and mechanical properties produced from experimental slabs. A comprehensive study shows that continuously cast slab's solidification rate determines the dispersion of the dendritic structure and the microscopic inhomogeneity degree. It is established that the dendritic structure density is the degree indicator of cast steel’s microchemical homogeneity. In all structural zones and in the whole thickness of a continuous slab with a thickness of 105 mm, the dendritic structure density and the micro-chemical homogeneity increases with increasing crystallization rate. Using the methods of quantitative metallography, it is shown that with an increase in the crystallization rate, the resulting cast structure becomes significantly dispersed. The study revealed a pattern between the initial austenitic structure of a continuously cast slab obtained at different crystallization rates and the structure of hot-rolled rolled products obtained by direct rolling, when hot slabs are placed in a heating furnace before phase transformations γ→α in the steel structure.

Optically Pumped Magnetometer Measuring Fatigue-Induced Damage in Steel

Uniaxial fatigue testing of micro-mechanical metallic specimens can provide valuable insight into damage formation. Magnetic and piezomagnetic testing are commonly used for qualitative characterization of damage in ferromagnetic specimens. Sensitive and accurate measurements with magnetic sensors is a key part of such a characterization. This work presents an experimental setup to induce structural defects in a micro-mechanical fatigue test. Simultaneously, the resulting piezomagnetic signals are measured during the complete lifetime of the tested specimen. The key component is a highly sensitive optically pumped magnetometer (OPM) used to measure the piezomagnetic hysteresis of a small specimen whose structural defects can be analyzed on a small scale by other metallographic characterization methods as well. This setup aims to quantify the magnetic signatures of damage during the fatigue process, which could enable non-destructive mechanical testing of materials. This paper reports the initial results obtained from this novel micro-magneto-mechanical test setup for a ferritic steel specimen.

Investigation of the joinability of single- and multi-layered AA6014 sheets produced by accumulative roll bonding in the shear-clinching process

Accumulative roll bonding belongs to the severe plastic deformation processes and is suitable for producing multi-layered as well as high-strength sheets through repeated rolling. After four accumulative roll bonding-cycles, the strength of the investigated AA6014-T4 alloy is elevated due to strain and fine grain hardening by 170% in yield strength and by 37% in ultimate tensile strength. This is accompanied by a significant decrease in material ductility which is disadvantageous for joining processes based on forming operations. Shear-clinching, however, can be used to join high-strength and low-ductile materials on the die side. Thus, it is a promising method for the mechanical joining of accumulative roll bonding components. The multi-layered and more brittle material is located on the die side whereas the single-layered base material with higher ductility is positioned on the punch side. At present, there is no scientific knowledge how the multi-layered material behaves in the shear-clinching process. Since the material is cut in the process, delamination effects could occur at the interfaces produced via accumulative roll bonding. Additionally, the investigation aims at the influence of the accumulative roll bonding process on the properties of the joints. They are expected to depend on the number of process cycles and thus on the change of mechanical properties of the multi-layered material. The bond strength of the shear-clinched joints is determined by shear and tensile tests. The areas of material failure are analysed via metallographic methods. From the failure behaviour and load-bearing capacity it is determined which number of accumulative roll bonding cycles is ideal for joining multi-layered sheets via shear-clinching.

Isothermal crystallization behavior of undercooled liquid Pd40Cu30Ni10P20 in terms of crystal growth, overall volume crystallization kinetics and their relation to the viscosity temperature dependence

Abstract The crystallization behavior of undercooled liquid Pd40Cu30Ni10P20 metallic alloy has been studied with the aid of differential scanning calorimetry, optical metallography, and electron microscopy methods. The crystallization occurs as a single-stage process starting preferably on the surface of casting voids in the sample volume and on the outer sample cutting planes. The linear crystal growth velocity of crystallizing cells was measured at several constant temperatures in the range 590 –620 K. It is constant at constant temperatures and its temperature dependence is in good agreement with the theoretical concepts of Uhlmann using the temperature dependence of the viscosity of the alloy studied. A differential scanning calorimetry study of isothermal overall volume transformation kinetics of samples pre-annealed at 600 K for 600 s was carried out at several constant temperatures. The experimental data are interpreted on the basis of the equation of Kolmogorov-Avrami-Johnson-Mehl for the case of three-dimensional growth of a fixed number of pre-existing nuclei. The possibility to revitrify the crystallized samples by their melting in differential scanning calorimeter, followed by quick cooling with cooling rate of 5 K τ– 1 is shown. The volume transformation kinetics of revitrified samples has been also studied.

Investigation of crystal structure formation by electropulse treatment of amorphous Ti50Ni25Cu25 alloy ribbons

The study of the effect of electropulse treatment with a variable duration on the crystallization processes and the structure of a amorphous TiNiCu alloy with 25 at.% Cu in comparison with isothermal annealing and heating at a constant speed was carried out. The alloy was fabricated by rapid-quenching from the liquid state (melt spinning technique) at the cooling rate of the melt of about 106 °C/s in the form of a ribbon with a thickness of 28 μm with a surface crystal layer with a thickness of about 2-3 μm. To remove the crystal layer, the method of double-sided electrochemical polishing was used. The studies were carried out by methods of differential scanning calorimetry, metallography and scanning electron microscopy. It was established that the formation of the crystalline phase in the electropulse treatment of the amorphous ribbon occurs from the surface to the inner part due to the predominant formation and growth of columnar crystals with subsequent nucleation and growth of crystals in the rest of the ribbon.

Peculiarities of transformation of metastable austenite into deformation martensite during laser cladding with cored wire 60Cr7TiAl

Fe-Cr-C-T-Al flux-cored wire surfacing was performed by laser, arc and hybrid methods. Laboratory tests have shown that the deposited layers vary greatly in terms of wear resistance. To identify the reasons, studies were carried out using metallographic, X-ray structural and durometric methods. The analysis of the research results showed that the reason is the difference in the cooling rates of the deposited metal in the range of 1100-800 K. This difference leads to the possibility of the formation of a metastable austenitic structure, which, in turn, affects the wear resistance of the deposited layers. Keywords: cored wire, wear resistance, metallography, X-ray diffraction, microhardness, laser cladding, arc deposition, hybrid deposition.

Exsolution in alkali feldspar in ordinary chondrites: Ubiquitous evidence for rapid cooling at high temperatures

Thermal metamorphism in undisrupted ordinary chondrite (OC) parent bodies is thought to occur through the radioactive decay of 26Al, producing an onion-shell-like structure with higher peak metamorphic temperatures corresponding to increasing depth. During retrograde metamorphism, the onion-shell model predicts slower cooling rates with increasing petrologic type. However, cooling rates determined by pyroxene diffusion, metallographic, and other methods are inconsistent with onion-shell-like cooling, leading to a model of asteroid disruption and reaccretion into a rubble pile, after peak metamorphism. Potassium-feldspar exsolution in albite, in a perthite texture, has been noted in OCs and can be used as another method for determining cooling rates. We conducted a survey of K-feldspar occurrences and textures, within chondrules, in petrologic type 3.6–6 H, L, and LL OCs. Potassium-feldspar is present as a secondary feature, in primary and secondary albite, as fine-scale exsolution lamellae, 0.1–1.5 μm wide, as well as in larger patches up to 50 μm in size. Exsolution is present in all OC groups and is most common in petrologic type 4.In the H4 chondrite Avanhandava, we estimate the cooling rate from perthite to be 3–17 °C/yr over a temperature interval of 765–670 °C. Peristerite is also present in Avanhandava for which we estimate a cooling rate of 0.2–2.4 × 10−3 °C/yr from 570-540 °C. In general, the relatively fast, high-temperature cooling rate determined by perthite is similar to cooling rates recovered from two-pyroxene speedometry. The peristerite cooling rate is closer to the slow, lower temperature metallographic cooling rates. Because K-feldspar exsolution is present in similar fine-scale lamellae in all OC groups, we suggest that all OC parent bodies experienced the same cooling history at high temperatures. These results are inconsistent with predictions of OC asteroid cooling from undisturbed onion-shell metamorphism but are consistent with models involving disruption after peak metamorphism followed by reassembly.

Mproving the properties of steels by producing in their structure along with other components of metastable austenite and the following hardening

The relevance. Improving the mechanical properties of steels and their wear resistance makes it possible to increase the service life of machine parts, which is an important task of materials science. One of the promising directions in its solution is combined processing technologies of steels based on the principle of obtaining in them in various ways a structure containing, along with other components (various types of martensite, lower bainite, in some cases carbides) of an increased amount (³ 25 %) of metastable austenite, and subsequent strengthening. In this case, a certain amount of austenite transforms into deformation martensite, and the its remaining part undergoes dynamic deformation martensitic transformation (DDMT) – the effect of self-hardening under loading (SHL). Combined processing technologies include thermal (in some cases, chemical-thermal) and deformation effects on the metal, carried out in various combinations and sequences. Processing technologies for obtaining an increased amount of metastable austenite in the structure of steels can include: holding in the intercritical temperature interval (ICTI) with various hardening methods, plastic deformation stabilizing austenite with respect to the formation of cooling martensite, thermal cycling, etc. Strengthening of steels with an increased amount of metastable austenite is carried out by cold plastic deformation, after which tempering is carried out in some cases. However, the principle is currently being considered and the combined processing technologies that implement it are not used in industry. This excludes the use of metastable austenite, which is an internal resource of the material itself, and its transformation under loading, which increases its ability to self-defense against destruction during testing of properties and operation. In this regard, it is advisable to introduce the proposed combined processing technologies into practice, which will ensure resource saving. In work on a number of steels their effectiveness has been shown.
 Рurpose is to show the possibility of increasing the mechanical properties or wear resistance of the studied steels by using combined processing technologies based on the principle that provides for the production of an increased amount of metastable austenite in their structure and subsequent hardening, which preserves the possibility of DDMT and the implementation of the effect SHL.
 Research methods. Durometric, metallographic and X-ray research methods were used. The tensile properties and impact strength, as well as abrasive wear resistance, were determined. These properties were compared with those obtained for the studied steels after a typical heat treatment.
 Results. It is shown that the proposed combined treatment technologies, including the production of an increased amount of metastable austenite in the structure of the studied steels and subsequent hardening, which retains the possibility of DDMT and the implementation of the effect SHL, increase the mechanical properties or wear resistance in comparison with their level after the commonly used treatment.
 Scientific novelty. To improve the mechanical properties or wear resistance of alloys an innovative principle was proposed, which consists in obtaining in them an increased amount of metastable austenite before strengthening treatments, preserving after them a part of it that can undergo DDMT and, accordingly, realize the effect SHL when testing properties and operation.
 Practical value. For the studied steels, rational modes of combined processing technologies have been determined, including obtaining an increased amount of metastable austenite in their structure and subsequent hardening, which have shown their effectiveness in increasing mechanical properties or wear resistance in comparison with commonly used treatments.

Analyzing metallurgical interaction during arc surfacing of barrier layers on titanium to prevent the formation of intermetallics in titanium-steel compounds

This paper considers a possibility to obtain high-quality butt junctions of bimetallic sheets from steel clad with a layer of titanium, with the use of barrier layers. The task that was tackled related to preventing the formation of Ti-Fe intermetallic phases (IMPs) between the steel and titanium layer. The barrier layers (height ~0.5 mm) of vanadium and copper alloys were surfaced by arc techniques while minimizing the level of thermal influence on the base metal. To this end, plasma surfacing with a current-driving wire and pulsed MAG surfacing were used. The obtained samples were examined by methods of metallography, X-ray spectral microanalysis, durometric analysis. It has been established that when a layer of vanadium is plated on the surface of titanium, a defect-free structure of variable composition (53.87–65.67) wt % Ti with (33.93–45.54) wt % V is formed without IMPs. The subsequent surfacing of steel on a layer of vanadium leads to the formation of eutectics (hardness up to 5,523 MPa) in the fusion zone, as well as to the evolution of cracks. To prevent the formation of IMPs, a layer of bronze CuBe2 was deposited on the surface of vanadium. The formed layer contributed to the formation of a grid of hot cracks. In the titanium-vanadium-copper transition zones (0.1–0.2 mm wide), a fragile phase was observed. To eliminate this drawback, the bronze CuBe2 was replaced with bronze CuSi3Mn1; a defect-free junction was obtained. When using a barrier layer with CuSi3Mn1, a defect-free junction was obtained (10–30 % Ti; 18–50 % Fe; 5–25 % Cu). The study reported here makes it possible to recommend CuSi3Mn1 as a barrier layer for welding bimetallic sheets "steel-titanium". One of the applications of the research results could be welding of longitudinally welded pipes of main oil and gas pipelines formed from bimetallic sheets of steel clad with titanium.

Database Clustering after Automatic Feature Analysis of Nonmetallic Inclusions in Steel

Non-metallic inclusions (NMIs) in steel have a negative impact on the properties of steel, so the problem of producing clean steels is actual. The existing metallographic methods for evaluating and analyzing nonmetallic inclusions make it possible to determine the composition and type of NMIs, but do not determine their real composition. The analysis of single NMIs using scanning electron microscope (SEM), fractional gas analysis (FGA), or electrolytic extraction (EE) of NMIs is too complicated. Therefore, in this work, a technique based on the automatic feature analysis (AFA) of a large number of particles by SEM was used. This method allows to obtain statistically reliable information about the amount, composition, and size of NMIs. To analyze the obtained databases of compositions and sizes of NMIs, clustering was carried out by the hierarchical method by constructing tree diagrams, as well as by the k-means method. This made it possible to identify the groups of NMIs of similar chemical composition (clusters) in the steel and to compare them with specific stages of the steelmaking process. Using this method, samples of steels produced at different steel plants and using different technologies were studied. The analysis of the features of melting of each steel is carried out and the features of the formation of NMIs in each considered case are revealed. It is shown that in all the studied samples of different steels, produced at different steel plants, similar clusters of NMIs were found. Due to this, the proposed method can become the basis for creating a modern universal classification of NMIs, which adequately describes the current state of steelmaking.

A Metallographic Preparation Method for Three-Dimensional Microstructural Characterization of Machining Chips

Abstract Chip formation is an important indicator of machining processes. Statistical characterization of machining chips’ geometric features can offer crucial information for evaluating the stability and productivity of the machining processes. In abrasive machining processes, an abundance of small chips are produced by the vast number of abrasives exposed to the cutting surfaces. Geometric features of abrasives, such as shape, dimension, and distribution, may be hierarchically passed on to the chips. Similar to those of the abrasives, geometric features of the chips may also vary to a certain extent and conform to some statistical distribution. To verify these characteristics, a metallographic preparation method in connection with chips formed in abrasive machining processes is proposed in this study. Challenges in collecting and segmenting chips have been successfully overcome through several steps using ultrasonic bath cleaning and powder cold embedding methods. Finally, a considerable amount of chips was formed and uniformly embedded in a resin mold, ready for microscopic characterization.

A NEW METHOD FOR MANUFACTURING OF ROPES USED IN NET OR ROPE CLIMBING GAME GROUPS

Nowadays, climbing game tracks are available for children and for young people and adults. Some of these game tracks are climbing tracks designed as a net. Other ones are climbing groups comprising ropes and similar structures that are suitable for gripping by the hand. There are also game tracks that include both basic game tracks or have different designs while maintaining the fundamental characteristics. However, their common characteristic is that they allow people to try to grasp the rope or net tightly and play or do exercise with an experience close to the natural environment. For this reason, yarns (strings) made of materials such as nylon, polypropylene or polyester are either directly knitted or adhered with chemical adhesives on steel wires. However, during its use, the knitted or adhered yarns (strings) on the steel wire are opened, disorganized or worn. This causes the wires to corrode and / or wear under ambient conditions and thus shorten the life of the ropes. In this study, a solution has been developed to provide a rigid coating of these yarns on the wires. In our study, after the threads were wound on the wires, the steel wires were heated by an electromagnetic induction current and thus, the threads on the steel wires were softened with the effect of the heat. Then, during cooling, the threads harden and partially adhere to each other. Due to this heating process, the temperature was kept under control in order to prevent the properties of the steel wires from deteriorating. After the wires were produced, they were tested with tensile test, hardness and metallographic examination methods, and changes in their properties were controlled.

Quantitative Examination of the Inclusion and the Rotated Bending Fatigue Behavior of SAE52100

This study investigated the effect of maximum inclusion on the life of SAE52100 bearing steel processed by two different melting routes, vacuum induction melting plus electroslag remelting (VIM + ESR), and basic oxygen furnace plus ladle furnace plus vacuum degassing process (BOF + LF + RH) by the metallographic method, Aspex explorer, and rotated bending fatigue test. The rotated bending method was applied to examine the maximum inclusion size in a satisfactory manner, whereas both the metallographic method and Aspex explorer underestimated the result. Regardless of the characterization methods, the results show that the total number of inclusions in VIM + ESR melted steel is significantly higher than that in BOF + LF + RH processed steel, but the maximum inclusion size of VIM + ESR melted steel is significantly smaller than that of the BOF + LF + RH degassed steel. The distribution of the maximum inclusion size could be well fitted by the inverse Weibull distribution and could be well applied to reveal the different inclusion size distribution based on the data examined by the rotated bending fatigue method. Finally, a new equation was proposed to establish the relationship among the loading stress amplitude, rotated bending fatigue number, and the maximum inclusion size.

К проблеме разрушения инструмента при получении неразъемных соединений толстостенных заготовок алюминиевых сплавов сваркой трением с перемешиванием

Introduction. Among the technologies for manufacturing rocket and aircraft bodies, marine vessels, and vehicles, currently, more and more attention is paid to the technology of friction stir welding (FSW). First of all, the use of this technology is necessary where it is required to produce fixed joints of high-strength aluminum alloys. In this case, special attention should be paid to welding thick-walled blanks, as fixed joints with a thickness of 30.0 mm or more are the target products in the rocket-space and aviation industries. At the same time, it is most prone to the formation of defects due to uneven heat distribution throughout the height of the blank. It can lead to a violation of the adhesive interaction between the weld metal and the tool and can even lead to a destruction of the welding tool. The purpose of this work is to reveal regularities of welding tool destruction depending on parameters of friction stir welding process of aluminum alloy AA5056 fixed joints with a thickness of 35.0 mm. Following research methods were used in the work: the obtaining of fixed joints was carried out by friction welding with mixing, the production of samples for research was carried out by electric erosion cutting, the study of samples was carried out using optical metallography methods. Results and discussion. As a result of performed studies, it is revealed that samples of aluminum alloy with a thickness of 35.0 mm have a heterogeneous structure through the height of weld. There are the tool shoulder effect zone and the pin effect zone, in which certain whirling of weld material caused by the presence of grooves on tool surface is distinctly distinguished. It is shown that the zone of shoulders effect is the most exposed to the formation of tunnel-type defects because of low loading force and high welding speeds. It is revealed that tool destruction occurs tangentially to the surface of the tool grooves due to the high tool load and high welding speeds.

Increasing of the steels properties by an ecological method of isothermal and step quenching

The relevance. Improving the mechanical properties of steels makes it possible to increase the service life of machine parts, which is an important task in materials science. One of the promising directions in its solution is to obtain in steel a multiphase structure, one of the main components of which is metastable austenite, which undergoes a dynamic deformation martensitic transformation (DDMT) - self-hardening effect under loading (SHL). Methods providing the required structure are isothermal and step quenching. However, at present, when they are carried out for cooling from the austenitizing temperature and holding at the constant temperature used non-environmentally friendly substances: heated oil, molten salts or alkalis. In this regard the actual problem is the exclusion of them from the technological process. The possibility of solving this problem on several steels has shown.
 Purpose is to show the possibility of increasing the mechanical properties of the studied steels 30ХГСА, 38ХС, 45Г, 40ХН, 10Г12, 60Х18 by using rational modes of an environmentally friendly method of steels quenching (isothermal - for low-alloyed and step - for high-alloyed) due to obtaining in their structure along with other components of metastable residual austenite and the implementation of the SHL effect.
 Research methods. Samples of the investigated steels after austenitization (in some cases with holding in IСIT) were cooled in water to the temperature of lower bainite formation (isothermal quenching) or stabilization of supercooled austenite to martensitic transformation upon cooling (step quenching), after which they were kept in a furnace and cooled in air to room temperature. Durometric, metallographic and X-ray research methods were used. The tensile properties and impact strength were determined. These properties were compared with those obtained for the studied steels after a typical heat treatment, including quenching in oil and tempering.
 Results. It is shown that isothermal and step quenching of the investigated steels without the use of non-environmentally friendly substances, carried out according to rational modes, makes it possible to increase the mechanical properties in comparison with their level after the commonly used quenching in oil (fire hazard, the vapors are cancerogenic) and tempering. This is achieved by obtaining a multiphase structure with metastable austenite.
 Scientific novelty. It is proposed to obtain a multiphase structure with metastable austenite in them to improve the mechanical properties of the studied steels by conducting isothermal and step quenching in an environmentally friendly way without using heated oil, molten salts or alkalis.
 Practical value. For the studied steels the modes of isothermal and step quenching are determined in an environmentally friendly way, which make it possible to increase the mechanical properties in comparison with the level achieved by quenching and tempering. Wherein in contrast to a similar typical quenching method are excluded the costs of purchasing salts or alkalis, their disposal and washing of products from them. Compared to quenching and tempering, the new method does not require the use of oil and tempering. The latter improves ecology and reduces energy consumption during heat treatment.

The The effect of iron on precipitation hardening in the Cu-Ni-Mn alloys

The peculiarities in the structure and properties formation of precipitation-hardened Сu–Ni–Mn–Fe alloys within the concentration range of Ni (19.3–21.0 %), Mn (19.5–20.5 %), Fe (0.6–2.7 %), Cu – balance (in wt. %) were investigated in this work. The methods of quantitative metallography, X-ray analysis, scanning electron microscopy, energy-dispersive spectroscopy and differential thermal analysis were applied. Two solid solutions based on a-Cu differing in composition and hardness were found in the structure of the cast Сu–Ni–Mn–Fe alloys. The temperature ranges of solutions’ formation were determined as (1010±10) °С and (890±10) °С, correspondingly. NiMn phase was also formed at (405±15) °С due to precipitation hardening. In the Сu–Ni–Mn–Fe alloys annealed at 500 and 900 °С for 60–750 hours, the volume fraction and size of NiMn precipitates increased with prolonging annealing time and lowering annealing temperature. As iron content was raised up to 2.7 wt. %, the density of NiMn precipitates increased, especially during first 60 hours of annealing at 900 °С. By adding iron, oxidation resistance was improved, but melting temperature and fluidity did not yield any significant change. Hardness of the Сu–Ni–Mn–Fe alloys with higher iron contents increased by 10 НRB on average. However, when test temperature was raised up to 400 °С, tensile strength decreased (by ~1.3 times) and elongation dropped markedly (by ~10 times).

Study of the relationship among total oxygen, inclusions and fatigue properties of gear steel

In order to control non-metallic inclusions and improve fatigue performance of gear steel, the relationship among total oxygen, inclusion size and fatigue properties of gear steel was investigated. In the work, Mn–Cr system gear steels with different total oxygen contents were selected as the research objects. Inclusions and fatigue properties of gear steels with different total oxygen contents were studied by using traditional metallographic method, extreme value method and fatigue test. The experimental results demonstrates that with the decrease of total oxygen content（i.e., 0.0013%→0.0010%→0.0005%）, the number of small-size oxide inclusions in the range of 5–10 μm decreases greatly, whereas the number of large-size oxide inclusions over 10 μm has relatively little change. Meanwhile, it is found that the change of total oxygen content in different ranges has different influences on the size of maximum size oxide inclusion and fatigue properties. Reducing the total oxygen content of gear steel from 0.0013% to 0.0010% decreases the inclusion size of maximum oxide inclusion and improves fatigue resistance of materials, but these benefits do not extend to a total oxygen level of 0.0005%. Accordingly, we can conclude that no evident linear correlation exists between total oxygen content and maximum inclusion size or between the total oxygen content and the fatigue performance.