Effect Of High-temperature Thermomechanical Treatment Research Articles

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.

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

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 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.

The Microstructure and Mechanical Properties of Ferritic-Martensitic Steel EP-823 after High-Temperature Thermomechanical Treatment

The effect of high-temperature thermomechanical treatment (HTMT) with plastic deformation by rolling in austenitic region on the microstructure and mechanical properties of 12% chromium ferritic-martensitic steel EP-823 is investigated. The features of the grain and defect microstructure of steel are studied by Scanning Electron Microscopy with Electron Back-Scatter Diffraction (SEM EBSD) and Transmission Electron Microscopy (TEM). It is shown that HTMT leads to the formation of pancake structure with grains extended in the rolling direction and flattened in the rolling plane. The average sizes of martensitic packets and ferrite grains are approximately 1.5–2 times smaller compared to the corresponding values after traditional heat treatment (THT, which consists of normalization and tempering). The maximum grain size in the section parallel to the rolling plane increases up to more than 80 µm. HTMT leads to the formation of new sub-boundaries and a higher dislocation density. The fraction of low-angle misorientation boundaries reaches up to ≈68%, which exceeds the corresponding value after HTMT (55%). HTMT does not practically affect the carbide subsystem of steel. The mechanical properties are investigated by tensile tests in the temperature range 20–700 °C. It is shown that the values of the yield strength in this temperature range after HTMT increase relative to the corresponding values after THT. As a result of HTMT, the elongation decreases. A significant decrease is observed in the area of dynamic strain aging (DSA). The mechanisms of plastic deformation and strengthening of ferritic-martensitic steel under the high-temperature thermomechanical treatments are also discussed.

Structural Transformations and Mechanical Properties of Metastable Austenitic Steel under High Temperature Thermomechanical Treatment

The effect of high-temperature thermomechanical treatment on the structural transformations and mechanical properties of metastable austenitic steel of the AISI 321 type is investigated. The features of the grain and defect microstructure of steel were studied by scanning electron microscopy with electron back-scatter diffraction (SEM EBSD) and transmission electron microscopy (TEM). It is shown that in the initial state after solution treatment the average grain size is 18 μm. A high (≈50%) fraction of twin boundaries (annealing twins) was found. In the course of hot (with heating up to 1100 °C) plastic deformation by rolling to moderate strain (e = 1.6, where e is true strain) the grain structure undergoes fragmentation, which gives rise to grain refining (the average grain size is 8 μm). Partial recovery and recrystallization also occur. The fraction of low-angle misorientation boundaries increases up to ≈46%, and that of twin boundaries decreases to ≈25%, compared to the initial state. The yield strength after this treatment reaches up to 477 MPa with elongation-to-failure of 26%. The combination of plastic deformation with heating up to 1100 °C (e = 0.8) and subsequent deformation with heating up to 600 °C (e = 0.7) reduces the average grain size to 1.4 μm and forms submicrocrystalline fragments. The fraction of low-angle misorientation boundaries is ≈60%, and that of twin boundaries is ≈3%. The structural states formed after this treatment provide an increase in the strength properties of steel (yield strength reaches up to 677 MPa) with ductility values of 12%. The mechanisms of plastic deformation and strengthening of metastable austenitic steel under the above high-temperature thermomechanical treatments are discussed.

The Effect of Finely Divided Martensite of Austenitic High Manganese Steel on the Wear Resistance of the Excavator Buckets Teeth

An analytical review of the effect of high-temperature thermomechanical treatment on the structure and properties of steels as a possible effective method of strengthening the teeth of excavator buckets. It is shown that the application of this method can have a positive effect not only on the hardness, but also on the entire complex of their mechanical characteristics, such as plasticity, impact toughness and fatigue resistance. In relation to Hadfield steel as the most frequently used material of the bucket teeth, it is noted that with increasing deformation grade of billets from 1 to 5, tensile strength of steel increases from 570 to 1030 MPa, yield strength – from 480 to 790 MPa, relative elongation – from 14.3 to 17.9 %, relative contraction – from 17.2 to 20.1 %, impact strength KCU – from 1.51 to 2.14 MJ/m2. This article presents the results of metallographic analysis and comparative tests for abrasive wear of Hadfield steel samples after typical heat treatment practiced at bucket teeth manufacturers and thermomechanical treatment. It is established that high-temperature plastic deformation of steel samples before quenching increases their wear resistance by 1.7 times. The authors attribute the detected increase in wear resistance to the formation of fine martensite in the surface layers of steel with a needle size of 3-10 nm, which increases its hardness by 47%. It is concluded that the presence of fine martensite in the structure of Hadfield steel can increase the service life of excavator bucket teeth made of this material. The results of this study are planned to be used in the development of an improved technological process for manufacturing bucket teeth of excavators.

Влияние высокотемпературной термомеханической обработки на микроструктуру, механические свойства и особенности разрушения ферритно-мартенситной стали ЭП-823

Влияние высокотемпературной термомеханической обработки на микроструктуру, механические свойства и особенности разрушения ферритно-мартенситной стали ЭП-823

Effect of High-Temperature Thermomechanical Treatment on the Brittle Fracture of Low-Carbon Steel

The effect of high-temperature thermomechanical treatment (HTMT) on the brittleness connected with deformation-induced aging and on the reversible temper brittleness of a low-carbon tube steel with a ferrite–bainite structure has been studied. When conducting an HTMT of a low-alloy steel, changes should be taken into account in the amount of ferrite in its structure and relationships between the volume fractions of the lath and the acicular bainite. It has been established that steel subjected to HTMT undergoes transcrystalline embrittlement upon deformation aging. At the same time, HTMT, which suppresses intercrystalline fracture, leads to a weakening of the development of reversible temper brittleness.

Effect of high-temperature thermomechanical treatment in the austenite region on microstructure and mechanical properties of low-activated 12% chromium ferritic-martensitic steel EK-181

The effect of high-temperature thermomechanical treatment with deformation in the austenite region on the microstructure and mechanical properties in low-activated 12% chromium ferritic-martensitic steel EK-181 (Fe–12Cr–2W–V–Ta–B) has been investigated. This treatment leads to a significant increase (compared to traditional regime of treatment) in the density of dislocations, dispersity, and volume fraction of nanosized particles V(C,N) and, as a consequence, to an increase in the yield strength while maintaining a sufficient reserve of ductility.

Effect of high-temperature thermomechanical treatment on the mechanical properties of nitrogen-containing constructional steel

The effect of thermomechanical treatment on the structure and mechanical properties of the constructional steels (35 – 50)KhNMAF micro-alloyed with nitrogen is studied. Tensile and impact tests are conducted, the HV hardness is measured, and the structure of the steel is investigated by means of light microscopy and X-diffraction analysis. The regimes of thermal and thermomechanical treatment that make it possible to use this type of steel as a high-strength steel are determined.

Effect of high-temperature thermomechanical treatment on hydrogen embrittlement of a high-strength aluminum alloy

Effect of high-temperature thermomechanical treatment on hydrogen embrittlement of a high-strength aluminum alloy

Effect of high-temperature thermomechanical treatment on mechanical metallurgy characteristics of high-strength martensitic steels

AbstractThe high-temperature thermomechanical treatment of high-strength steels has proved to be superior to their conventional heat treatment in enhancing both their strength and their plastic properties, as well as in raising their fracture toughness KIC and the threshold values of KISCC and KISH, established by testing in a 3·5% aqueous solution of NaCl and during electrolytic hydrogen charging of the specimens, respectively. Tests proved that high-temperature treatment increased the KIC value for any selected ultimate tensile strength level by roughly 20 MPa/m1/2, while the strength properties concurrently improved by some 12–15%. The mechanical metallurgy investigations were supplemented by a fractographic analysis. The favourable effect of high-temperature thermo mechanical treatment on the mechanical metallurgy properties is attributed to both the refinement of the martensitic structure and the limitation of the dynamic effects of the platelets in the course of the martensitic phase transformation.

Effect of high-temperature thermomechanical treatment and microalloying with a rare earth metal on the corrosion and corrosion-fatigue strength of steel 1Kh17N2

1. High-temperature thermomechanical treatment and microalloying with 0.1% La raise the fatigue and corrosion-fatigue strength of steel 1Kh17N2. 2. The rise in the fatigue strength is due to an increase in the resistance to crack growth resulting from changes in the structure and substructure brought about in the steel by the high-temperature treatment and microalloying with the rare earth metal. 3. High-temperature thermomechanical treatment of steel 1Kh17N2 and its alloying with 0.1% La raise the corrosion resistance of the steel and reduce its tendency to intercrystalline corrosion. 4. The increase in the corrosion resistance of steel 1KM7N2 after the high-temperature treatment and microalloying with the rare earth metal is caused by the structural changes produced in the steel by the treatment and the microalloying.

Effect of high-temperature thermomechanical treatment on the cyclic strength of spring steel 50KhGA

1. High-temperature thermomechanical treatment of steel 50KhGA (rolling at 900 °, 40% reduction, holding for 2 sec after deformation) substantially improves the cyclic strength as compared with the standard heat treatment (the fatigue limit increases by 60% and the low-cyclic fatigue strength under a stress of 60 kg/mm2 by a factor of 15–60). 2. High fatigue strength is obtained in the case where the material has a fairly high ductility along with high ultimate strength. This combination of properties can be obtained with a developed substructure.

Stress-corrosion cracking of thermomechanically treated steels

The effect of high-temperature thermomechanical treatment (HTMT) on the susceptibility of high-strength chromium-silicon steels to stress-corrosion cracking was studied. The considerable improvement produced by this treatment was attributed to the resulting reduction in the sensitivity of steels of this kind to the presence of notches formed by corrosion under stress. Comparison of results obtained for specimens tested in tension and torsion made it possible to assess various theories of long-term strength for heat-treated steel (quench-hardened and subjected to low-temperature tempering) under the influence of corrosive media.

Effect of high-temperature thermomechanical treatment on the mechanical properties of chromium-manganese-silicon steel

1. We showed the possibility of using HTTMT with a reduced austenite deformation temperature (in the range of Ac3−Ar3) for chromium-manganese-silicon steel, which increases σb and σ0.2 by comparison with higher deformation temperatures (above Ac3). The use of reduced austenite deformation temperatures in HTTMT also substantially inhibits the development of recrystallization processes. 2. The characteristics of plasticity, ductility, and resistance to brittle fracture (sensitivity to notches and cracks) show the advantage of an austenite deformation temperature of 900°C by comparison with the other temperatures investigated (1000, 820, and 780°C).

Effect of high-temperature thermomechanical treatment (HTMT) on the fatigue strength of high-carbon steels

Fatigue tests on steels 9KhS and ShKh15 revealed anisotropy in fatigue properties of these steels after HTMT.

Effect of high-temperature thermomechanical treatment on the fine structure and mechanical properties of titanium alloys

1. It was established that the strength increases with increasing degrees of deformation during HTTMT, the maximum increase occurring with 30% deformation. Subsequent age hardening increases the strength. The plasticity of the alloy also increases somewhat after HTTMT and subsequent age hardening in comparison with the standard treatment. 2. High-temperature thermomechanical treatment of both alloys creates a stable configuration of defects, which guarantees retention of the advantages of HTTMT with increasing temperatures. However, at the highest temperature the VT3-1 alloy recrystallizes more rapidly after HTTMT than after the standard treatment because of the higher rate of diffusion in the structure with defects.

Effect of high-temperature thermomechanical treatment on the resistance to rupture of high-carbon steels strained by torsion

1. High-temperature thermomechanical treatment induces considerable toughening of high-carbon steels and orientation of the structure. With forward loading the toughening is manifest as an increased resistance to rupture with greater plastic deformation as compared to the hardened steel. 2. High-temperature thermomechanical treatment reduces the plasticity and strength of high-carbon steels in the case of reverse loading. 3. A considerable reduction of high-carbon steels during HTTMT is unacceptable because it leads to damage of the material, which is most evident in the case of reverse loading. For steels containing 0.9–1.0% C the optimum degree of strain γ=0.3–0.6, which matches a generalized deformation e=15–30%.