The effect of Nb, V, N and Al on the creep rupture strength of 9–12 % Cr steel

Kuboň, Zdeněk; Foldyna, Václav

doi:10.1002/srin.199501143

Cited by 13 publications

(9 citation statements)

References 8 publications

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“…Recently, the Laves (Fe 2 W, Fe 2 Mo) phases have drawn a growing interest as strengthener to improve the creep resistance of the steels. 6,7) Even though these high strength steels have been widely used for turbine rotor in power plants, material degradation is obviously known to occur due to their continuous exposure to high temperatures (e.g., thermal ageing and creep). Therefore, the characterization of damage mechanism is crucial for accessing the life and structural integrity of the components.…”

Section: Introductionmentioning

confidence: 99%

Dynamic Coercivity of Advanced Ferritic Steel during Long-Term Isothermal Ageing

et al. 2009

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The object of this study is to characterize the microstructural evolution in advanced ferritic steel for power plant during long-term isothermal ageing by measuring the reversible permeability. Ageing was observed to coarsen the tempered carbide (Cr 23 C 6 ), generate the Laves (Fe 2 W) phase, and reduce the mechanical strength. The dynamic coercivity decreased monotonously during isothermal ageing. The decrease in coercivity physically depends on the domain wall movement, related with the domain wall pinning by nonmagnetic particles and the dislocations. The experimental results show that the dynamic coercivity is very sensitive to the damage accumulations due to isothermal ageing of advanced ferritic steel.

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Section: Introductionmentioning

confidence: 99%

Dynamic Coercivity of Advanced Ferritic Steel during Long-Term Isothermal Ageing

et al. 2009

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“…The creep testing was conducted at 923 K with 120 MPa using single-lever testing machines. Precipitation behavior was studied by quantitative chemical analysis of extracted residue, assuming simple stoichiometric compositions of MX and M 23 C 6 . Morphology of fine MX was investigated by a Transmission Electron Microscope (TEM).…”

Section: Methodsmentioning

confidence: 99%

“…Extracted residue using a solution of 10 % acetylacetone was also prepared for total quantitative analysis of carbides and nitrides. By assuming a simple stoichiometric composition such as MN or MC and no substitution of Nb and V into M 23 C 6 at tempering stage, absolute mass fractions and their chemical balance in MX and M 23 C 6 were derived from comparing quantitative results between two different residues. Figure 2 shows the change in mass fraction of Cr, Fe and W between NT and QT specimens for the steels with different C/N.…”

Section: Quantitative Analysis Of Precipitatesmentioning

confidence: 99%

“…Transformation from (Fe, Cr) 3 C to M 23 C 6 at tempering stage is mainly controlled by concentration of metallic elements such as Cr and W in the case of the present steels, and then it is supposed that formation of M 23 C 6 is quickly occurred because diffusion of Cr and W is accelerated by the exposure at high temperature region during air-cooling. On the other hand, Cr and W are thought to remain in solution uniformly in the quenched specimen and it may take longer time to precipitate M 23 C 6 with an equilibrium composition at tempering.…”

Section: Precipitation Kineticsmentioning

confidence: 99%

“…4,5) Recently, it has been pointed out that an effective solid solution of nitrogen is important to determine the contribution of VN to the creep rupture strength. 6) It is, however, noted that there is no intensive study about the effect of cooling rate from normalization temperature on creep properties in the practical high-Cr ferritic steels because its creep behavior is thought to be insensitive to initial microstructure. In this study, we compare the precipitation behavior of MX-type carbonitride and M 23 C 6 at tempered stages between two different heat treatments using simple model steels with different C/N-balance, and then clarify that the fine distribution of MX is important to improve the creep resistance of the high-Cr ferritic steels.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Heat Treatment on Precipitation Kinetics in High-Cr Ferritic Steels.

Yamada¹,

Igarashi²,

Muneki

et al. 2002

ISIJ International

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Precipitation strengthening is important to improve creep strength of heat resisting steels at elevated temperatures. Especially, in the high-Cr ferritic steels recently developed for Ultra Super Critical Power Plants, precipitation behavior is complicated and should be clarified because the correlation between various strengthening factors are still not well understood. In this study, we focus on the change in precipitation behavior of MX type carbonitrides in model steels with different heat treatment conditions.It is found that dominant precipitation behavior has been changed with cooling rate from normalization temperature before tempering and better creep properties have been obtained in the steel quenched rather than in the one air-cooled. It is confirmed that precipitation of M 23 C 6 is suppressed and total fraction of MX is relatively increased by the quenching procedure. It is thought that better creep resistance is mainly due to fine distribution of MX that is achieved by suppressing typical co-precipitation of MX such as Nb(C, N)-VN during cooling after normalization and tempering.

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Evaluation of structural stability and creep resistance of 9-12% Cr steels

et al. 1996

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During creep exposure of modified chromium steels lowering of solid solution strengthening due to precipitation of Laves phase as well as coarsening of all precipitates causes degradation of creep resistance. Two distinct domains of the stress dependence of creep rate and time to rupture have been observed in precipitation strengthened modified chromium steels. The stress characterizing the transition between these domains was found to be closely related to the Orowan stress. This stress consists in these steels of the contribution from large particles on subgrain boundaries (mainly M23C6 and during the limited time also Laves phase) and from small precipitates (Nb(C,N) and VN) inside subgrains. This has to be considered when measuring the interparticle spacing and calculating Orowan stress. Larson‐Miller parametric equation is used to elucidate the necessity of long‐term creep testing. By means of two heats of CrMoVNbN steel it is shown that reliable extrapolation of creep properties is possible only in a stress and temperature domain in which only one creep creep rupture mechanism operate. In the high stress domain Larson‐Miller constant CLM is well above 30 while in the low stress domain this constant does not exceed 25. When the extrapolation is based mainly on short‐term creep tests, the CLM constant is close to that valid in the high stress domain and therefore it overestimates long‐term creep strength.

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The effect of Nb, V, N and Al on the creep rupture strength of 9–12 % Cr steel

Cited by 13 publications

References 8 publications

Dynamic Coercivity of Advanced Ferritic Steel during Long-Term Isothermal Ageing

Dynamic Coercivity of Advanced Ferritic Steel during Long-Term Isothermal Ageing

Effect of Heat Treatment on Precipitation Kinetics in High-Cr Ferritic Steels.

Evaluation of structural stability and creep resistance of 9-12% Cr steels

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