High-temperature Thermomechanical Treatment Research Articles

Transient Nucleate Boiling and Its Use for Thermomechanical Technologies Development

In the paper high temperature and low temperature intensive thermomechanical treatment is discussed. It is based on recently discovered new three physical principles that belong to the transient nucleate boiling process taking place in cold fluids. Such processes are considered in conditions when any film boiling during quenching in cold fluids is completely absent. That makes nucleate boiling very intensive, i.e. . The discoveries are used for direct quenching articles after forgings. The first is intensive high-temperature thermo-mechanical treatment (HTTMT). It is used for low and middle-carbon alloy steels. Forged steel parts are intensively quenched with a cooling interruption at the proper time to form surface compression residual stresses and fine bainitic microstructure at the core that increases radically surface life of forgings. The second method includes high-temperature and low temperature intensive thermo - mechanical treatment (LTTMT) of high carbon alloy steels with delaying martensitic transformation to make low-temperature thermo - mechanical treatment (LTTMT) possible. Then, after high temperature and low-temperature thermomechanical treatment, the steel goes to immediate tempering to create highly strengthened fine bainitic microstructure throughout the section of the steel part. A modified method of cooling time calculation, suitable for any size and form of steel part, is widely discussed in this paper.

Evaluation of Structural Powder Steel Properties after High-Temperature Thermomechanical Treatment and Finish Turning

Evaluation of Structural Powder Steel Properties after High-Temperature Thermomechanical Treatment and Finish Turning

Formation of structure and physical and mechanical properties of reinforcing steels during high-temperature thermomechanical treatment

The effect of high-temperature thermomechanical treatment (HTMT) modes on the formation of the structure and physical and mechanical properties of reinforcing St5 steel is considered. It is shown that with HTMT in the mode of intensive (interrupted) cooling, there is a significant difference in hardness (47 HRC on the surface versus 31 HRC in the core) and a significant change in mechanical properties (σв, σ0,2, δ5). It is established that under conditions of maximum intensive cooling, the reinforcing bar does not have time to completely calcinate. The use of continuous cooling mode allows for a more uniform distribution of mechanical properties. The production of high-strength reinforcement of А800, А1000, Аt1200 strength classes after the HTMT is ensured by the formation of a dispersed martensitic-troostite structure in steel.

УПРОЧНЕНИЕ ЦИЛИНДРИЧЕСКИХ ДЕТАЛЕЙ ТРАКТОРОВ И СЕЛЬСКОХОЗЯЙСТВЕННЫХ МАШИН

The structures of tractors, automobiles, combine harvesters and other agricultural machines contain a large number of solid and hollow cylindrical parts without complex structural elements, for example, the swing axis 52-2301058 of the front axle of a wheeled tractor. The actual resource of these parts often does not correspond to that declared by the manufacturer. (Research purpose) The research purpose is increasing the service life of the swing axis 52-2301058 by developing a manufacturing process using high-temperature thermomechanical processing with screw compression. (Materials and methods) Used rolled steel 45 for the manufacture of hardened swing axes 52-2301058. The rolled products were cut on a band saw, then the blanks were subjected to high-temperature thermomechanical treatment with screw compression. Induction tempering of machining zones and further machining were performed on a lathe and vertical milling machines. Mechanical characteristics were studied by tensile testing of samples; hardness was determined by the Rockwell method. (Results and discussion) We have developed a route technological process consisting of seven operations. The samples manufactured according to this technological process were subjected to tensile tests and hardness determination. According to the research results, the hardness of the samples is in the range of 48-52 on the Rockwell scale, while there is an increase in tensile strength and conditional yield strength by 30 percent, relative elongation and relative contraction by two times compared with conventional quenching in water and tempering at a temperature of 300-400 degrees Celsius. (Conclusions) The developed technological process made it possible to increase the life of the swing axis 52-2301058 three times, which corresponds to 10,000 operating hours.

The Cold-Brittleness Regularities of Low-Activation Ferritic-Martensitic Steel EK-181

The behavior of the EK-181 low-activation ferritic-martensitic reactor steel (Fe–12Cr–2W–V–Ta–B) in the states with different levels of strength and plastic properties after traditional heat treatment (THT) and after high-temperature thermomechanical treatment (HTMT) in the temperature range from −196 to 25 °C, including the range of its cold brittleness (ductile–brittle transition temperature, DBTT) is studied. The investigations are carried out using non-destructive acoustic methods (internal friction, elasticity) and transmission and scanning electron microscopy methods. It is found that the curves of temperature dependence of internal friction (the vibration decrement) of EK-181 steel after THT and HTMT are similar to those of its impact strength. Below the ductile–brittle transition temperature, it is characterized by a low level of dislocation internal friction. The temperature dependence curves of the steel elastic modulus increase monotonically with the decreasing temperature. In this case, the value of Young’s modulus is structure-sensitive. A modification of the microstructure of EK-181 steel as a result of HTMT causes its elastic modulus to increase, compared to that after THT, over the entire temperature range under study. The electron microscopic studies of the steel microstructure evolution near the fracture surface of the impact samples (in the region of dynamic crack propagation) in the temperature range from −196 to 100 °C reveal the traces of plastic deformation (increased dislocation density, fragmentation of the martensitic structure) at all of the temperatures under study, including those below the cold brittleness threshold of EK-181 steel.

Effect of low and high temperature ECAP modes on the microstructure, mechanical properties and functional fatigue behavior of Ti-Zr-Nb alloy for biomedical applications

A Ti-18Zr-15Nb (at%) shape memory alloy was subjected to a high-temperature thermomechanical treatment (HTMT) combining an equal channel angular pressing (ECAP) at 500 °C for n = 4–8 passes and a short-time post-deformation annealing (PDA) at 600 °C. The phase composition, microstructure, texture, mechanical and functional properties were studied. The functional fatigue behavior observed in this study was compared to that resulted from the reference low-temperature thermomechanical treatment (LTMT) by ECAP at 200 °C for 3 passes + PDA (600 °C for 5 min). The ECAP at 500 °C (n = 4) led to the formation of a highly deformed, dynamically polygonised substructure of β-phase with a crystallographic texture close to the [101] direction. In this state, the alloy exhibited an excellent combination of the static functional and mechanical properties: a relatively high strength (UTS = 670 MPa), a sufficient ductility (δ = 13.3 %), a low Young’s modulus (E < 40 GPa), and a high superelastic recovery strain (εrsemax= 3.1 %). An increase in the number of passes during ECAP to n = 8 led to a greater substructural hardening of the material, grain/subgrain refinement, and the release of α-phase. This significantly increased the alloy strength (UTS = 897 MPa), but reduced its ductility (δ = 5.9 %) and suppressed martensitic transformation. The alloy after both the HTMT (ECAP at 500 °C, n = 4) and TMT (ECAP at 200 °C, n = 3) processes exhibited an equally excellent functional fatigue resistance accompanied by a superior superelastic behavior with small accumulated strains. However, the HTMT process appears to be more technologically advanced, as it eliminates the need for PDA and reduces the risks of specimen cracking during processing.

Features of structure formation in antifriction composite powder infiltered with copper alloy material based on iron (pseudo-alloy) under high-temperature thermomechanical treatment

The results of studies of the structure formation process in an iron-based antifriction composite powder material infiltrated with a copper alloy (pseudo-alloy) during thermal and high-temperature thermomechanical treatment (HTMT) are presented. It is shown that after infiltration the structure of the pseudo-alloy consists of sections of the steel skeleton with a perlite structure almost homogeneous in carbon and a small amount of cementite, sections of the copper phase located along the boundaries and at the joints of the particles of the steel skeleton, sulfide inclusions mainly in the copper phase. In the process of hardening, carbon is redistributed in the particles of the steel skeleton; a layer 2–5 µm thick with an increased carbon content is formed at the boundary with the copper phase. During HTMT, the structure is refined, a macrotexture is formed, and the thickness of the copper phase interlayers decreases, depending on the degree of deformation. The degree of deformation also affects the structure of the steel skeleton. After HTMT with a degree of deformation of 30 %, the structure consists of structureless martensite, troosto-martensite and residual austenite, and in the areas adjacent to the copper phase the carbon content is slightly lower, with a degree of deformation of 50 % – structureless martensite, 25 % more austenite content, more uniform distribution of carbon. It has been established that, due to the activation of diffusion processes during deformation during HTMT, molybdenum sulfides decompose and form iron and copper sulfides of various compositions; molybdenum alloys the iron base or forms carbide. The investigation results can be used in the development of high-strength antifriction materials for heavily loaded friction units.

The Effect of High-Temperature Thermomechanical Treatment on the Microstructure and Mechanical Properties of Cu–Al–Ni–(B) Alloys with a Thermoelastic Martensitic Transformation

Polycrystalline boron-alloyed α + β Cu–Al–Ni compositions subjected to high-temperature thermomechanical treatment (HTMT) via forging and rolling are studied for the first time. Optical, scanning, and transmission electron microscopy and X-ray diffraction analysis were used in combination with measurementsof tensile mechanical properties to study the peculiarities of the microstructure, phase composition, and mechanical properties of these alloys. The peculiarities of the microstructure and mechanical behavior of alloys differing in their aluminum and boron contents, which were subjected to HTMT, have been determined.The alloys were prepared in the fine-grained state, which determines the increase in the functional strength and plastic characteristics. A schedule of HTMT of bulk Cu–Al–Ni–(B) alloys is proposed.

The Effect of High-Temperature Thermomechanical Treatment on the Microstructure and Mechanical Properties of Cu–Al–Ni–(B) Alloys with a Thermoelastic Martensitic Transformation

The Effect of High-Temperature Thermomechanical Treatment on the Microstructure and Mechanical Properties of Cu–Al–Ni–(B) Alloys with a Thermoelastic Martensitic Transformation

Development and Research of New Hybrid Composites in Order to Increase Reliability and Durability of Structural Elements

Hybrid composite materials can successfully solve the problems of reliability, durability, and extended functionality of products, components, and details, which operate under conditions of multifactorial influences (temperature, force, and deformation). The authors have developed a hybrid composite high-entropy AlCoCrCuFeNi material and ceramic cBNCoMo(B4CCoMo) layer. The formation of hybrid composites was carried out using new technology. This technology includes high-energy machining, high-velocity oxygen-fuel spraying in a protective environment, high-temperature thermomechanical treatment, and heat treatment. The use of the developed technology made it possible to increase the adhesive strength of the composite layers from 68 to 192 MPa. The authors performed an assessment of the structural parameters of the composite layers. The assessment showed that the composite layers had a nanocrystalline structure. The research included mechanical tests of the hybrid composites Hastelloy X (NiCrFeMo)—AlCoCrCuFeNi—cBNCoMo and Hastelloy X (NiCrFeMo)—AlCoCrCuFeNi—B4CCoMo for cyclic durability (fatigue mechanical tests) and friction wear. The use of surface-layered materials AlCoCrCuFeNi—cBNCoMo and AlCoCrCuFeNi—B4CCoMo in the composition of hybrid composites significantly increased cyclic durability. The use of surface-layered materials in the composition of hybrid composites made it possible to reduce wear intensity. The test results show that the developed composites are promising for use in various industries (including oil and gas), where high strength and wear resistance of materials are required.

Regularities of change in physical-mechanical and corrosion properties of heat-strengthened reinforcing 20GS2 steel

The effect of the regularities in changes of the physical-mechanical and corrosion properties of 20GS2 reinforcing steel subjected to heat treatment is considered. It is found that steel has the highest sensitivity to cracking, regardless of the type of tempering (from electric heating or furnace), in the temperature range of 400...450 °С, and with a subsequent increase in tempering temperature, cracking resistance increases. The electron microscopic studies made it possible to establish that at 450 °С the martensitic orientation of cementite plates completely disappears, coherence is lost, block boundaries disintegrate, sizes and shapes of cementite plates change, and precipitation of carbides along grain boundaries begins. Such an unstable structure has an increased ability to absorb hydrogen (results of gas analysis), which leads to an acceleration of the process of hydrogen cracking. Therefore, electric heating of 20GS2 steel after high-temperature thermomechanical treatment is required to be carried out to temperatures of 500...550 °С.

Study of the structure and mechanical properties of composites used in the oil and gas industry

&lt;abstract&gt; &lt;p&gt;This article describes the structure and properties of the developed hybrid composite Hastelloy X (NiCrFeMo)-AlMoNbTaTiZr-cBNSiCNiAlCo. The composite was obtained by the high velocity oxygen fuel spraying (HVOF) method in a protective atmosphere with a subsequent high-temperature thermomechanical treatment. In order to obtain new information about the structure, we studied the metallophysical properties of the composite using electron microscopy and X-ray diffraction analysis, as well as the mechanical properties and phase composition. We studied the influence of high-energy mechanical processing of high-entropic and ceramic materials on the structural-phase state and composite quality. We determined the optimal technological parameters of HVOF in a protective atmosphere, followed by a high-temperature thermomechanical treatment. Additionally, we optimized these parameters to form a hybrid composite providing the highest adhesion and low porosity. Moreover, we investigated the microhardness of the composite layers. On the basis of complex metallophysical studies, we examined the composite formation. In order to determine the endurance limit in comparison to various other composite materials, we carried out cyclic endurance tests of the developed materials.&lt;/p&gt; &lt;/abstract&gt;

Mechanisms of hardening of 12 % chromium ferritic-martensitic steel EP-823

Based on experimental data on microstructure parameters of the reactor high-strength high-chromium (12 % Cr) ferritic-martensitic steel EP-823, the authors identified the main factors responsible for its strength properties. The hardening mechanisms of this steel were analyzed after processing according to the modes that provide different level of steel strength properties. Traditional heat treatment (THT) and promising modifying high-temperature thermomechanical treatment (HTMT) are considered. The main mechanisms of steel hardening, regardless of the processing mode, are: dispersed hardening by nanoscale particles of the MeX type (Me = V, Nb, Mo; X = C, N) by the Orovana mechanism; grain-boundary hardening by high-angle boundaries of martensitic blocks and ferrite grains; substructural hardening by small-angle boundaries of martensitic lamellae; dislocation hardening by increased dislocation density. HTMT mode, which includes hot deformation in the austenitic area, leads to a significant modification of the structural-phase state of steel relative to THT: a decrease in the average size of blocks and lamellae of martensite, as well as ferrite grains, an increase in the density of dislocations and the volume fraction of nanoscale particles of the MeX type. At the same time, the corresponding contributions to value of the steel yield strength from grain boundary, substructural and dispersed hardening increase by 1.2, 1.3 and 1.8 times in comparison with THT. The relative contributions of the considered hardening mechanisms to the yield strength of ferritic-martensitic steel EP-823 were discussed. The values closest to the experimental yield strength after two treatment modes studied are obtained when the Langford-Cohen model is used to estimate the magnitude of substructural hardening.

Fracture features of impact samples of low-activation ferritic-martensitic steel EK-181 after high-temperature thermomechanical treatment

A comparative fractographic investigation of fracture in the temperature range from −186 to 100°C of the Charpy impact samples is performed for the reactor low-activation ferritic-martensitic steel EK-181 after its high-temperature thermomechanical treatment (HTMT) and traditional heat treatment (THT). The mechanisms of steel fracture are revealed depending on the impact test temperature and treatment mode. On the upper and lower shelves of the impact toughness temperature curve, the steel fractures by the mechanism of transcrystalline ductile dimple fracture and transcrystalline quasi-cleavage, respectively. In the intermediate region (in ductile-brittle transition area), fracture occurs by a mixed mechanism. The transition temperature to the brittle state is determined, at which the proportion of ductile and brittle fractures is the same (after THT it is −3°C; after HTMT it is −14°C). It is established that HTMT significantly changes the type of fracture of the impact samples in comparison with THT. The microstructure formed during HTMT with hot deformation of austenite leads to the appearance of a crack-arrester type of delamination during the impact tests in the cold brittleness region, favoring an increase in the fracture toughness of the steel at a lower ductile-brittle transition temperature.

The Microstructure, Tensile and Impact Properties of Low-Activation Ferritic-Martensitic Steel EK-181 after High-Temperature Thermomechanical Treatment

In this work, we study the effect of high-temperature thermomechanical treatment (HTMT) with deformation in the austenite region on the microstructure, tensile properties, impact toughness, and fracture features of advanced low-activation 12% chromium ferritic-martensitic reactor steel EK-181. HTMT more significantly modifies the steel structural-phase state than the traditional heat treatment (THT). As a result of HTMT, the hierarchically organized structure of steel is refined. The forming grains and subgrains are elongated in the rolling direction and flattened in the rolling plane (so-called pancake structure) and have a high density of dislocations pinned by stable nanosized particles of the MX type. This microstructure provides a simultaneous increase, relative to THT, in the yield strength and impact toughness of steel EK-181 and does not practically change its ductile-brittle transition temperature. The most important reasons for the increase in impact toughness are a decrease in the effective grain size of steel (martensite blocks and ferrite grains) and the appearance of a crack-arrester type delamination perpendicular to the main crack propagation direction. This causes branching of the main crack and an increase in the absorbed impact energy.

Simulation of the Dynamic Recrystallization of Austenitic Corrosion-Resistant Steel during the Formation of a Complex Section by High-Temperature Thermomechanical Treatment

Simulation of the Dynamic Recrystallization of Austenitic Corrosion-Resistant Steel during the Formation of a Complex Section by High-Temperature Thermomechanical Treatment

Optimization of a thermomechanical treatment of superelastic Ti-Zr-Nb alloys for the production of bar stock for orthopedic implants

Ti-19Zr-14 Nb (at%) shape memory alloy was subjected to low- and high-temperature thermomechanical treatments to fabricate long-length bar stock for the production of load-bearing orthopedic implants. The phase composition, structure, texture, uniaxial tensile and three-point bending fatigue behavior were studied. Low-temperature thermomechanical treatment (LTMT), combining cold rotary forging and post-deformation annealing at 550 °C led to the formation in the peripheral zone of the bar cross-section of a statically recrystallized fine-grained structure with a relatively strong [001] crystallographic texture and of a mixed statically recrystallized and polygonized substructure, in the central zone of the cross-section. In this state, the alloy exhibited an excellent combination of the static functional and mechanical properties: relatively high strength (UTS=680 MPa), low Young’s modulus (E < 40 GPa), and high superelastic recovery strain (εrsemax=3.4%). High-temperature thermomechanical treatment (HTMT), consisting in hot rotary forging at 700 °C, led to the formation of a dynamically polygonized substructure with a uniform crystallographic texture close to the [101] direction; this direction corresponding to the maximum theoretical recovery strain limit. As compared to the LTMT bar stock, its HTMT equivalent manifested slighly inferiour static properties but superior fatigue resistance in bending, thus being an optimal candidate for the production of orthopedic implants.

Strengthening of Thick-Walled Pipes by High-Temperature Thermomechanical Treatment with Gradient Tempering in Wall Thickness

Strengthening of Thick-Walled Pipes by High-Temperature Thermomechanical Treatment with Gradient Tempering in Wall Thickness

Texture Development in Aluminum Alloys with High Magnesium Content

The evolution of texture in the AlMg6Mn0.7 (1565 ch) alloy throughout the entire cycle of its thermomechanical treatment has been studied. Using this alloy as an example, a new way is shown to control the texture development, which is applicable to alloys with high magnesium content. An integrated approach is applied, including optical and electron microscopy, as well as X-ray diffraction analysis, the determination of mechanical properties and texture modeling using algorithms of the crystallographic plasticity theory. All stages of the thermomechanical treatment have been studied, namely the development of the deformation structure out of the as-cast structure in the reversing hot-rolling stand, continuous hot rolling, cold rolling and final recrystallization annealing. The study showed that second phase particles are the main source of recrystallization nuclei at all stages of high temperature thermomechanical treatment. The importance of these particles increases when the Zener-Hollomon parameter increases. To obtain the maximum possible proportion of a random texture, thermomechanical processing must be carried out at high Zener-Hollomon parameters. However, the temperature should not interfere with the complete recrystallization process at the same time. After cold rolling and recrystallization annealing at temperatures equal or greater than 350 °C, a large proportion of random texture is formed, and the properties of the metal are almost isotropic.

Effect of High Temperature Thermomechanical Treatment on the Tendency of Low-Activation 12% Cr Ferritic-Martensitic Steel EK-181 to Low-Temperature Embrittlement

Effect of High Temperature Thermomechanical Treatment on the Tendency of Low-Activation 12% Cr Ferritic-Martensitic Steel EK-181 to Low-Temperature Embrittlement