Characterization of the carbides in the steel X20CrMoV12.1 used in thermal power plants

“…In an earlier paper [7] the microstructures of steam pipes (the chemical composition of the steel is presented in Table 1) that had been in service for several years were investigated, with the focus being on determination of the carbide types. In the next stage of this microstructural investigation an 'in situ' study of the carbide growth or the change of the composition and phase was planned.…”

Section: Resultsmentioning

confidence: 99%

Study of the carbide coarsening during the annealing of X20CrMoV12.1 steel

Skobir

Godec

Nagode

et al. 2010

Surface & Interface Analysis

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The steel X20CrMoV12.1 has been widely used for the steam pipes in power plants since 1960s. It exhibits a good combination of high-temperature strength, toughness and creep strength. The microstructure consists of high-tempered martensite with finely dispersed carbide precipitates along the boundaries of the ex-austenitic grains and the ferritic sub-boundaries. The carbides change their chemical and phase composition as well as their size with time and temperature until equilibrium is reached. However, this process lasts for thousands of hours. For this reason, we simulated these conditions in the laboratory using higher temperatures in order to accelerate the process. After different annealing times the carbide precipitates and their orientational relationships with the neighbouring grains were examined by electron-backscatter diffraction (EBSD). After 24 h of annealing all the carbides were M 23 C 6 and were in an orientational relationship with the matrix. The volume fraction of carbides is independent of annealing time and temperature.

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Constitutive analysis of hot metal flow behavior of virgin and rejuvenated heat treatment creep exhausted power plant X20 steel

Maube,

Obiko,

Van der Merwe

et al. 2024

Int J Adv Manuf Technol

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This paper presents constitutive equations that describe the hot ow behaviour of Virgin (VG) X20 and rejuvenated heat-treated creep exhaust (CE) X20 steels. The study provides a foundation for determining the effect of rejuvenation heat treatment on CE steels by making comparisons to the VG steel. Hot compression tests in the temperature range of 900°C to 1050°C, strain rate range of 0.1-10 s − 1 to a total strain of 0.6 and stress-strain curves were obtained. The ow stress curves of both steels exhibited dynamic recovery (DRV) characteristics as the main softening mechanism. Constitutive constants of steady-state stresses were determined. The stress exponents, n, were 6.62 (VG) and 5.58 (CE), and the apparent activation energy values were 380.36 kJmol − 1 (VG) and 435.70 kJmol − 1 (CE). Analysis of the activation energies showed that VG steel had better workability properties than CE steel and was easier to deform at high temperatures. Constitutive equations for predicting the ow stress in the two steels were established. This were veri ed by statistical tools: Pearson's correlation coe cient (R) and Absolute Average Relative Error (AARE). The results showed R-values were, 0.98 (VG) and 0.99 (CE), and the AARE value for VG was 4.17% and 9.01% for CE. The statistical parameters indicated a good correlation between the experimental and predicted values. The constitutive equations therefore adequately described the ow stress behaviour of both steels and can therefore e ciently analyse industrial metal forming schedules.

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Characterization of the carbides in the steel X20CrMoV12.1 used in thermal power plants

Cited by 5 publications

References 5 publications

Micro-structural characterization of laboratory heats of the Ferric/Martensitic steels HT-9 and T91

Micro-structural characterization of laboratory heats of the Ferric/Martensitic steels HT-9 and T91

Study of the carbide coarsening during the annealing of X20CrMoV12.1 steel

Constitutive analysis of hot metal flow behavior of virgin and rejuvenated heat treatment creep exhausted power plant X20 steel

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