Microstructure and Mechanical Properties of Austenitic Steel EK-164 After Thermomechanical Treatments

Аккузин, С. А.; Litovchenko, I. Yu.; Tymentsev, A. N.; Чернов, В. М.

doi:10.1007/s11182-019-01766-0

Cited by 12 publications

(5 citation statements)

References 9 publications

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“…Under conditions of cold plastic deformation in metastable austenitic steels, dislocation gliding is not the only deformation mechanism of plastic deformation; there are also strain-induced γ → ε (face-center-cubic (fcc) → hexagonal-closed-packed (hcp)) and γ → ε → α (fcc → hcp → body-center-cubic (bcc)) martensitic transformations [1,2,5,[7][8][9][10][11]. In austenitic steels with low stacking fault (SF) energy under these conditions, a high density of microtwin packets is formed [12][13][14][15]. It is shown that with increasing deformation degree the microstructure of 304-type steel progressively changes: Dislocations (Ds) → Ds + SFs + ε → Ds + SFs + Twins + ε → Ds + SFs + Twins + ε + α → Ds + Twins + α [16].…”

Section: Introductionmentioning

confidence: 99%

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

Litovchenko

Аккузин

Polekhina

et al. 2021

Metals

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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.

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Section: Introductionmentioning

confidence: 99%

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

Litovchenko

Аккузин

Polekhina

et al. 2021

Metals

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“…Table 3 presents the average values of the yield strength, tensile strength and elongation to failure for new steel and the corresponding values of the mechanical properties of other reactor steels, taken from [12,21]. A comparison of these properties with the corresponding mechanical properties of the chromium-nickel austenitic steel EK-164 [20,21], currently used in nuclear power engineering, and the properties of the low-activation chromium-manganese austenitic steels of the 12Cr-20Mn type [11,12], demonstrates the advantages of the new steel (Table 3). Its higher values of the room-temperature strength properties are apparently due to the increased dislocation density and the higher density of dispersed carbide particles that pin the dislocation substructure.…”

Section: Resultsmentioning

confidence: 99%

New low-activation austenitic steel for nuclear power engineering

et al. 2022

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Vacuum induction melting is used to fabricate a new low-activation chromium-manganese austenitic steel with an increased, compared to well-known analogues, manganese content and additional alloying with strong carbide-forming elements (with a high tendency to carbide formation). Using the methods of transmission and scanning electron microscopy, the features of its microstructure, elemental and phase compositions in the solution treated state are studied. It is shown that the steel has an austenitic structure with a grain size of tens of micrometers. Its dislocation substructure is represented by flat dislocation pileups, which is typical for materials with low stacking fault energy. Coarse (submicron) particles of MC carbides (M = Ti, Ta, Zr, W) are found along the boundaries and inside the grains. Nanosized particles of the MC type fix the grain and subgrain boundaries and the dislocation substructure of the steel. Mechanical tensile tests are carried out at room and elevated temperatures. It is shown that the new steel has higher yield and tensile strength values, as well as elongation to failure compared to the austenitic chromiumnickel steels currently used in nuclear power engineering and well-known chromium-manganese low-activation steels.

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“…The volume fraction of these particles does not exceed 1%. Earlier [19], it was shown by TEM that fine (from several nm to 50 nm) MX particles based on vanadium were also observed in the structure of steel EK-164. These particles are not identified by EBSD methods due to their small size.…”

Section: Sem Ebsd and Tem Studies Of Deformed Microstructurementioning

confidence: 91%

Effect of Multistage High Temperature Thermomechanical Treatment on the Microstructure and Mechanical Properties of Austenitic Reactor Steel

Аккузин

Litovchenko

Polekhina

et al. 2021

Metals

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The deformation microstructures formed by novel multistage high-temperature thermomechanical treatment (HTMT) and their effect on the mechanical properties of austenitic reactor steel are investigated. It is shown that HTMT with plastic deformation at the temperature decreasing in each stage (1100, 900, and 600 °C with a total strain degree of e = 2) is an effective method for refining the grain structure and increasing the strength of the reactor steel. The structural features of grains, grain boundaries and defective substructure of the steel are studied in two sections (in planes perpendicular to the transverse direction and perpendicular to the normal direction) by Scanning Electron Microscopy with Electron Back-Scatter Diffraction (SEM EBSD) and Transmission Electron Microscopy (TEM). After the multistage HTMT, a fragmented structure is formed with grains elongated along the rolling direction and flattened in the rolling plane. The average grain size decreases from 19.3 µm (for the state after solution treatment) to 1.8 µm. A high density of low-angle boundaries (up to ≈ 80%) is found inside deformed grains. An additional cold deformation (e = 0.3) after the multistage HTMT promotes mechanical twinning within fragmented grains and subgrains. The resulting structural states provide high strength properties of steel: the yield strength increases up to 910 MPa (at 20 °C) and up to 580 MPa (at 650 °C), which is 4.6 and 6.1 times higher than that in the state after solution treatment (ST), respectively. The formation of deformed substructure and the influence of dynamic strain aging at an elevated tensile temperature on the mechanical properties of the steel are discussed. Based on the results obtained, the multistage HTMT used in this study can be applied for increasing the strength of austenitic steels.

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Microstructure and Mechanical Properties of Austenitic Steel EK-164 After Thermomechanical Treatments

Cited by 12 publications

References 9 publications

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

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

New low-activation austenitic steel for nuclear power engineering

Effect of Multistage High Temperature Thermomechanical Treatment on the Microstructure and Mechanical Properties of Austenitic Reactor Steel

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