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

Gaffard, Vincent; Besson, Jacques; Gourgues-Lorenzon, Anne-Françoise

doi:10.1007/s10704-005-2528-8

Cited by 37 publications

(19 citation statements)

References 70 publications

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“…In fact, the notch has a strengthening effect but it also shifts the transition between high and low stress creep regimes towards shorter creep lifetimes. 48) …”

Section: Creep Fracture Propertiesmentioning

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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“…In fact, the notch has a strengthening effect but it also shifts the transition between high and low stress creep regimes towards shorter creep lifetimes. 48) …”

Section: Creep Fracture Propertiesmentioning

confidence: 99%

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

2005

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“…Another problem relates to the occurrence of diffusional creep for which a Norton exponent of 1 is expected. This could be confirmed for grade 91 material [33]. It can be expected that for long creep lives such effects have to be taken into consideration for component life-time assessments.…”

Section: Stress Rupture and Creepmentioning

confidence: 54%

Damage assessment in structural metallic materials for advanced nuclear plants

Hoffelner

2010

J Mater Sci

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Future advanced nuclear plants are considered to operate as cogeneration plants for electricity and heat. Metals and alloys will be the main portion of structural materials employed (including fuel claddings). Due to the operating conditions these materials are exposed to damaging conditions like creep, fatigue, irradiation and its combinations. The paper uses the most important alloys: ferritic-martensitic steels, superalloys, oxide dispersion strengthened steels and to some extent titanium aluminides to discuss its responses to these exposure conditions. Extrapolation of stress rupture data, creep strain, swelling, irradiation creep and creep-fatigue interactions are considered. Although the stress rupture-and the creep behavior seem to meet expectations, the long design lives of 60 years are really challenging for extrapolations and particularly questions like negligible creep or occurrence of diffusion creep need special attention. Ferritic matrices (including oxide dispersion strengthened (ODS), steels) have better irradiation swelling behavior than austenites. Presence and size of dispersoids having a strong influence on high-temperature strength bring only insignificant improvements in irradiation creep. A strain-range-separation based approach for creep-fatigue interactions is presented which allows a real prediction of creep-fatigue lives. An assessment of capabilities and limitations of advanced materials modeling tools with respect to damage development is given.

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“…On the analogy between plastic and creep constitutive equations, the plastic yield potential of the GursonTvergaard-Needleman's damage model [10][11][12] can be modified as a creep potential and is written as (1) where q is the von-Mises equivalent stress, f* is the modified ductile void volume fraction, p is the hydrostatic pressure and σ m is the true stress in the matrix material which is a function of equivalent creep strain ε cr eq in the matrix material (i.e., the material isochronous stress-strain curve). The creeping behaviour of the matrix material is described in terms of two constants A and n according to Norton's law and it can be written as (2) The constants q 1 , q 2 and q 3 were introduced by Tvergaard and Needleman [11,12] in order to simulate the observed experimental fracture behaviour in many different materials more accurately.…”

Section: Potential For Creepmentioning

confidence: 99%

“…(1)] can be written in terms of mean hydrostatic and deviatoric parts of stress tensor and other field variables as (8) where p and q are the hydrostatic pressure and von Mises equivalent stress respectively and are defined as (9) H α 's are the thermodynamic internal state variables such as hardening parameter, void volume fraction f etc., I is the Kronecker-delta or second order identity tensor, S is the deviatoric part of stress tensor σ. The generalized flow rule for the increment of creep strain tensor from time t to t+Δt can be written as [16] (10) where ε ⋅ p and ε ⋅ q are the hydrostatic and equivalent parts of creep strain increment (the superscript 'p' and the tensorial subscripts 'ij' have been omitted for simplicity). The direction vector of creep flow at time t + Δt, i.e., n t + Δt is defined in terms of the deviatoric part of the elastic predictor stress s tr and von Mises equivalent stress q tr (corresponding to elastic predictor stress σ tr ) as (11) where the superscript 'tr' refers to the trial state of the quantities.…”

Section: Consistent Materials Tangent Stiffness Matrix For the Creepinmentioning

confidence: 99%

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A coupled damage model for creep

Samal

Dutta

Kushwaha

2010

Trans Indian Inst Met

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Alloy steels of type 9Cr1Mo are being developed worldwide for the boiler and turbine components of supercritical and ultra supercritical thermal power plants and for the pressure vessel of fast breeder reactors. These steels exhibit very complex high temperature creep cavitation processes with coupled influences of creep strain, material softening and ageing etc. A new viscoplastic model considering both deformation and damage evolution has been developed in this work to predict high temperature creep deformation and damage of a 9Cr1Mo steel. Smooth tensile specimens have been analysed using this new model and the evolution of creep damage has been predicted. The results have been compared with those of experiment from literature. From the initial results, it is observed that this approach is very promising to carry out design and fitness-for-purpose of service of actual plant components.

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

Cited by 37 publications

References 70 publications

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

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

Damage assessment in structural metallic materials for advanced nuclear plants

A coupled damage model for creep

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