High-Chromium (9-12Cr) Steels: Creep Enhancement by Conventional Thermomechanical Treatments

Vivas, Javier; San-Martín, David; Caballero, Francisca G.; Capdevila, Carlos

doi:10.5772/intechopen.91931

Cited by 5 publications

(3 citation statements)

References 64 publications

(83 reference statements)

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“…Among others, they are relatively inexpensive due to the lack of Ni and have a smaller thermal expansion coefficient, which is important in running up and shutting down cycles. Unfortunately, these steels can operate below 620 °C [ 1 , 2 ], which is insufficient in modern power generation systems. Creep strength is strongly decreased above 620 °C [ 3 , 4 ], and corrosion resistance is smaller due to a relatively low amount of Cr [ 5 ].…”

Section: Introductionmentioning

confidence: 99%

A Microstructural Investigation of Austenitic Heat Resistant Alloy after 500 h of Steam Oxidation

et al. 2021

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Alloy 709 was oxidized at 700 °C for 500 h in a steam environment. A microstructural analysis of the oxide scale is reported. Modern techniques of advanced electron microscopy were used to characterize the morphology of the oxide scale and recognize its single components. The material developed a complex, multilayered oxide scale. The outermost layer consisting of Fe2O3. Fe2NiO4 tI28 spinel was detected underneath. An internal oxidation zone is present in the innermost layer. High quality SEM-EDS maps give insight into a larger area of the oxide scale at a relatively low magnification.

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Section: Introductionmentioning

confidence: 99%

A Microstructural Investigation of Austenitic Heat Resistant Alloy after 500 h of Steam Oxidation

et al. 2021

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“…Dispersed nanoscale particles pining the dislocation substructure also play an important role in maintaining the high strength properties of steel. An increase in the strength in a wide range of test temperatures as a result of HTMT has been noted for many ferritic-martensitic steels [4,[14][15][16][17][18][19]23], while some authors [4] report an increase in ductility due to an increase in grain sizes.…”

Section: Discussionmentioning

confidence: 95%

“…After this treatment, the microstructure of the steels represents tempered martensite and ferritic grains with coarse carbides of M 23 C 6 type (M-Fe, Cr, Mn) and fine submicron particles of carbonitrides of MX type (M-V, Nb, Ta; X-C, N) [4][5][6][7][8]. It was shown [4][5][6][7][12][13][14][15][16][17][18][19][20][21] that various thermomechanical treatments, including those using plastic deformation in the austenitic region, make it possible to effectively change the above-mentioned parameters of the microstructure and the carbide subsystem of ferritic-martensitic steels. These changes mainly consist of a smaller width of martensitic packets and lamella, an increased dislocation density, a decreased size of coarse phases of the M 23 C 6 type and an increased dispersion of nanoscale carbides (carbonitrides) of the MX type [11,12,[15][16][17][22][23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

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

Litovchenko

Almaeva

Polekhina

et al. 2022

Metals

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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.

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

Almaeva

Litovchenko

Polekhina

et al. 2022

Izv. vysš. učebn. zaved., Čern. metall.

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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.

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High-Chromium (9-12Cr) Steels: Creep Enhancement by Conventional Thermomechanical Treatments

Cited by 5 publications

References 64 publications

A Microstructural Investigation of Austenitic Heat Resistant Alloy after 500 h of Steam Oxidation

A Microstructural Investigation of Austenitic Heat Resistant Alloy after 500 h of Steam Oxidation

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

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

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