Strain Enhanced Growth of Precipitates during Creep of T91

Nakajima, Takashi; Spigarelli, S.; Evangelìsta, E.; Endo, Takao

doi:10.2320/matertrans.44.1802

Cited by 30 publications

(16 citation statements)

References 31 publications

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“…Carbide coarsening is accelerated under applied load, which is consistent with Hättestrand and Andrén (2001), Nakajima et al (2003), Cerri et al (1998), Eggeler (1989) and Engberg et al (1984). For long term ageing (more than 10,000 h), stress no longer influences the coarsening kinetics and the final average size of the carbides is about 250 nm both with and without applied stress.…”

Section: Ageing and Softening Effectssupporting

confidence: 87%

Creep failure model of a tempered martensitic stainless steel integrating multiple deformation and damage mechanisms

2005

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International audienceA new model considering both deformation and damage evolution under multiple viscoplastic mechanisms is used to represent high temperature creep deformation and damage of a martensitic stainless steel in a wide range of load levels. First, an experimental database is built to characterise both creep flow and damage behaviour using tests on various kinds of specimens. The parameters of the model are fitted to the results and to literature data for long term creep exposure. An attempt is made to use the model to predict creep time to failure up to 105 h

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Section: Ageing and Softening Effectssupporting

confidence: 87%

Creep failure model of a tempered martensitic stainless steel integrating multiple deformation and damage mechanisms

2005

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“…[31][32][33][34] Both a large carbide size and a low carbon content promote rapid softening of martensite during a high temperature tempering treatment. 35) The hardness profile of Fig.…”

Section: Effects Of the Pwhtmentioning

confidence: 99%

“…Effects of the PWHT Several studies of the base metal have shown that the microstructural stability of 9Cr1Mo-NbV steels, especially under high temperature ageing and creep conditions, strongly depends on the pinning of dislocations and grain boundaries by a fine distribution of carbides. [31][32][33][34] Both a large carbide size and a low carbon content promote rapid softening of martensite during a high temperature tempering treatment. …”

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confidence: 99%

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

2005

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In the present study, creep flow and damage behaviour of modified P91 steel weldments are investigated. Premature creep failure of weldments (with respect to base metal) occurs in the intercritical heat affected zone (ICHAZ). This microstructure is reproduced by thermal simulation applied to blanks cut from the base metal. Metallurgical investigations of what happens during the welding cycle show that the weakest part of the heat affected zone is heated slightly below complete austenitisation, with little (if any) carbide dissolution. During the post-weld heat treatment, extensive recovery is allowed by carbide coarsening. The intrinsic creep behaviour of the resulting microstructure is experimentally determined under controlled constraint conditions. The welding cycle strongly decreases the creep strength by increasing the creep strain rate, but not necessarily by decreasing the ductility, at least for lifetimes up to 3 500 h.KEY WORDS: 9Cr1Mo-NbV martensitic steel; intercritical heat affected zone; Gleeble 1 500 thermalmechanical simulator; High temperature creep flow and damage.in the microstructure of interest was not known, just as for cross-weld specimens. The key point of the present study is thus to determine the properties of the weakest HAZ while eliminating, as much as possible, the constraint effects due to the surrounding materials. Material and Experimental Procedures MaterialsThe study focuses on a V-shaped, circumferentially welded joint of two pipes of 295 mm in outer diameter and 55 mm in thickness. It was fabricated by submerged metal arc welding in seventeen runs followed by a post weld heat treatment (PWHT) of 2 h at 760°C. The base metal is a tempered, modified P91 martensitic steel (see Table 1 for chemical composition). Its microstructure consists of lath martensite packets with M 23 C 6 (100 nm in mean size) and MX precipitates. The filler metal has nearly the same chemical composition as the base metal (Table 1). Simulation of Welding Thermal CyclesWelding thermal cycles were applied by using a Gleeble 1 500 thermal-mechanical simulator capable of heating specimens by Joule effect at very high heating rates, corresponding to those encountered in welding conditions (i.e. 100 to 250°C · s Ϫ1). The temperature is controlled by a thermocouple spot welded onto the specimen surface. Round bars of 5 mm in diameter were used to optimise the thermal cycle and 12 mm round blanks were treated and used to machine mechanical testing specimens respectively. For each of these two geometries, the closed-loop parameters of the Gleeble 1 500 simulator were carefully adjusted in order to ensure an uncertainty lower than 2°C for the value of T peak and smaller than 1 s for the value of the cooling parameter Dt 800→500 . For specimens of 5 mm in diameter, phase transformations were continuously monitored using in-situ dilatometric measurement of the specimen diameter. To prevent from extensive oxidation of the specimen, heat treatments were performed under primary vacuum (0.1 Pa). Phase transformations moni...

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“…The magnitude of L value is dependent of dislocation velocity, solute concentration in matrix, temperature and the size misfit of solutes, 25,26) however, it remains constant as long as the dislocation velocity remains unchanged. Using D l for grip parts and D 0 for gauge parts, the enhanced coarsening of precipitates in Al-Cu alloy, 14) Mod.9Cr-1Mo steel 22,23) and magnesium alloy of AZ80 24) can be explained reasonably by the scavenging effect. The detail will be published elsewhere.…”

Section: Scavenging Effectmentioning

confidence: 99%

“…One of the probable mechanisms is the scavenging effect of dislocation. [21][22][23] As mentioned already, an aluminum atom has a noticeable size misfit to the solvent atom of AZ80 alloy, so that a solute atmosphere is formed around a dislocation due to an elastic interaction. 24) Since the drift velocity of solutes given by the Einstein's equation is higher than the dislocation velocity at least within the solute atmosphere, the solute atmosphere lag behind dislocations.…”

Section: Scavenging Effectmentioning

confidence: 99%

Strain Enhanced Precipitate Coarsening during Creep of a Commercial Magnesium Alloy AZ80

2006

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Growth of precipitates during creep was investigated of a commercial magnesium alloy AZ80. TEM observations in this study confirmed that the cube of the average particle size changed roughly with creep time at grip parts and the growth rate was greater at the gauge part than at the grip part of crept specimens. The cube of the average particle size changed roughly with creep time at grip parts. This suggests that the coarsening of particles at grip part obeyed the Ostwald ripening theory in which the growth rate was assumed to be controlled by the lattice diffusion. In order to make clear the factors affecting the growth rate of precipitates at gauge part, interrupted creep tests were carried out. The present analysis of the experimental results showed that the effect of strain on the particle growth was more important than that of stress. The influence of concurrent straining on the particle growth is also discussed in terms of traveling dislocations with solute atmospheres.

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Strain Enhanced Growth of Precipitates during Creep of T91

Cited by 30 publications

References 31 publications

Creep failure model of a tempered martensitic stainless steel integrating multiple deformation and damage mechanisms

Creep failure model of a tempered martensitic stainless steel integrating multiple deformation and damage mechanisms

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

Strain Enhanced Precipitate Coarsening during Creep of a Commercial Magnesium Alloy AZ80

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