Kinetics of Z-Phase Precipitation in 9 to 12 pct Cr Steels

Danielsen, Hilmar Kjartansson; Nunzio, Paolo Emilio Di; Hald, John

doi:10.1007/s11661-012-1583-9

Cited by 66 publications

(67 citation statements)

References 14 publications

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“…In the 9CrVNbN alloy the Z-phase precipitation can be seen to appear at the end of the test durations, however the dissolution of MX has barely begun. Reconstructed from [43]. Reconstructed from [43].…”

Section: Precipitation Ratementioning

confidence: 99%

Review of Z phase precipitation in 9–12 wt-Cr steels

Danielsen

2016

Materials Science and Technology

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ABSTRACT9-12wt%Cr steels for high temperature applications in fossil fired power plants rely upon precipitate strengthening from (V,Nb)N MX nitrides for long term creep strength. During prolonged exposure at service temperature another nitride precipitates: Cr(V,Nb)N Z-phase. The Z-phase slowly replaces MX, eventually causing a breakdown in creep strength. This paper reviews the Z-phase and its behaviour in 9-12wt%Cr steels including thermodynamic modelling, crystal structure, nucleation process and precipitation rate as a function of chemical composition. The influence of Z-phase precipitation upon long-term creep strength is assessed from several different 9-12wt%Cr steel grades and alloy design philosophies.

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Section: Precipitation Ratementioning

confidence: 99%

Review of Z phase precipitation in 9–12 wt-Cr steels

Danielsen

2016

Materials Science and Technology

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“…At rupture time ≤5000 h, in the 9Cr2W steel, the V and Cr contents were essentially independent on the rupture time. Therefore, no gradual increase in Cr content within the V-rich MX particles resulting in transformation of their cubic lattice into tetragonal lattice of Z-phase [20,32,34] was detected.…”

Section: Crept Microstructuresmentioning

confidence: 92%

“…The average size of V-rich MX particles attained 60 nm after long-term creep tests in both steels. In the 9Cr2W steel, the well-known replacement of V-rich MX carbonitrides by Z-phase (CrVN nitride), which is in fact the most thermodynamically stable nitride [31,32], started to occur after~5000 h. The full transformation of all V-rich MX carbonitrides was found after 10,000 h of creep tests. The mean size of Z-phase was about 300 nm.…”

Section: Crept Microstructuresmentioning

confidence: 99%

Effect of Tungsten on Creep Behavior of 9%Cr–3%Co Martensitic Steels

Fedoseeva

Dudova

Kaibyshev

et al. 2017

Metals

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Abstract:The effect of increasing tungsten content from 2 to 3 wt % on the creep rupture strength of a 3 wt % Co-modified P92-type steel was studied. Creep tests were carried out at a temperature of 650 • C under applied stresses ranging from 100 to 220 MPa with a step of 20 MPa. It was found that an increase in W content from 2 to 3 wt % resulted in a +15% and +14% increase in the creep rupture strength in the short-term region (up to 10 3 h) and long-term one (up to 10 4 h), respectively. On the other hand, in the long-term creep region, the effect of W on creep strength diminished with increasing rupture time, up to complete disappearance at 10 5 h, because of depletion of excess W from the solid solution in the form of precipitation of the Laves phase particles. An increase in W content led to the increased amount of Laves phase and rapid coarsening of these particles under long-term creep. The contribution of W to the enhancement of creep resistance has short-term character.

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“…In addition, low creep ductility has been linked to cracking susceptibility of other established engineering steel systems. For example, in bainitic CrMoV steels [8][9][10][11], martensitic Grade 122 steel [12][13][14], and 316H stainless steel [15,16], a link between low creep ductility and in-service cracking has been established. However, the specific materials factors which enhance cavitation vary and the key knowledge necessary to justify improved control of manufacturing process for CSEF steels has only recently been established.…”

Section: Advances In Materials Science and Engineeringmentioning

confidence: 99%

Metallurgical and Stress State Factors Which Affect the Creep and Fracture Behavior of 9% Cr Steels

Parker

Siefert

2018

Advances in Materials Science and Engineering

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EPRI-supported research has identified critical material information regarding the factors affecting the performance of creep strength-enhanced ferritic steels, in general, and Grade 91 steel, in particular. EPRI recommendations emphasize that a five-point, integrated strategy should be used for the effective life management of components fabricated from tempered martensitic steels.is integration promotes a balanced use of resources which, when properly focused, reduces uncertainty regarding creep and fracture behavior. Tighter control of processes from steel making, steel processing, and heat treatment ensures that alloys with deficient properties never enter service. One cornerstone of this proactive approach is the definition of 'Metallurgical Risk' which links the presence of inclusions and trace elements to the susceptibility for creep damage. e improved confidence in the high temperature performance of CSEF steel components promotes reliability, increases efficiency, and minimizes the risk of component fracture. Background and IntroductionEPRI-coordinated, industry-sponsored research projects in creep strength-enhanced ferritic (CSEF) steels began in 2007 with a major effort to improve the life management of Grade 91 steel components. Since this initial project included more than 40 project participants and over $4 million in industry funding, several key follow-on projects have been completed or continue today. is series of related projects, illustrated in the schematic diagram shown in Figure 1, provides a critical base of information linking steel making and fabrication to microstructure and performance under simple and complex loading conditions. ese projects exemplify the EPRI mission statement "to provide thought leadership, industry expertise, and collaborative value to help the electricity sector . . . and addressed through effective research and development programs for the benefit of society."It is important to emphasize that the learnings and findings were realized with direct input and perspective from stakeholders representing the entire electricity supply chain. A general outcome from this research is that for metallurgically complex steels, testing programmes should establish high temperature performance on steel sections which are carefully chosen and well characterized, and the full pedigree of the steel cast selected is known. Full details of the research performed and the reports, position papers, and documents are available from the EPRI website. Selected achievements directly linked to materials factors are summarized below.(1) Detailed research examining the microstructure of tempered martensitic ferritic steels has provided key information concerning the rate controlling damage mechanisms for different conditions. Degradation during creep has been linked to many different factors; these include the formation of new phases, coarsening/dissolution of carbides, recovery of the dislocation substructure, and the nucleation, growth, and linking of microvoids [1][2][3][4]. Much of the prior...

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Kinetics of Z-Phase Precipitation in 9 to 12 pct Cr Steels

Cited by 66 publications

References 14 publications

Review of Z phase precipitation in 9–12 wt-Cr steels

Review of Z phase precipitation in 9–12 wt-Cr steels

Effect of Tungsten on Creep Behavior of 9%Cr–3%Co Martensitic Steels

Metallurgical and Stress State Factors Which Affect the Creep and Fracture Behavior of 9% Cr Steels

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