Creep-Fatigue Interactions in a 9 Pct Cr-1 Pct Mo Martensitic Steel: Part II. Microstructural Evolutions

Fournier, Benjamin; Sauzay, Maxime; Barcelo, Françoise; Rauch, E.F.; Renault, A.; Cozzika, T.; Dupuy, L.; Pineau, A.

doi:10.1007/s11661-008-9687-y

Cited by 92 publications

(50 citation statements)

References 40 publications

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“…The rate of decrease becomes slower before reaching a constant value during the second stage (Ntan). The constant decrease may be related to the internal microstructure changing as the coarsening of subgrains is observed and the dislocation density also decreases owing to cyclic deformation, as reported by Fournier, Sauzay [13]. The second stage occupies the largest proportion of the cycles.…”

Section: Resultsmentioning

confidence: 52%

“…The application of cyclic mechanical loading of P91 steel at high temperature causes microstructural and damage evolution throughout the material's life cycles. The microstructural evolution occurs on a subgrain scale and thus a transmission electron microscope is required to investigate this phenomenon [13]. The damage evolution can be indirectly measured based on Young's modulus values using the damage mechanics concept [14].…”

Section: Introductionmentioning

confidence: 99%

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A study on the damage evolution of P91 steel under cyclic loading at high temperature

Saad¹,

Bachok²,

Sun³

2016

Int. J. Automot. Mech. Eng.

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This study aimed to investigate the effect of cyclic loading on structural integrity of a P91 specimen at high temperature. The experiments were conducted using a thermomechanical fatigue test machine at 600 °C and electron microscopy investigation. The evolution of the elastic modulus can be used as an indication of the strength degradation of the material. Scanning and transmission electron microscopy were used to investigate the microstructural variations that occurred in the specimen at different life fractions during the cyclic tests. Based on the experimental stress-strain data, variations in the Young's modulus and the area enclosed in the hysteresis loops were determined, together with the variations in other parameters throughout the test. The initiation of cracks begins in the second stage of cyclic softening. The changes of structure, on a micro-scale, do not significantly affect the strength of the specimen, as the Young's modulus values of the specimen remain approximately constant up to the end of the stage 2 cyclic softening before damage to the specimen starts to increase. The cracks cause the material to become weaker, as indicated by the decrease of the Young's modulus value. The evolution of damage was found to be significant in the final stages of softening owing to the propagation of cracks in the P91 steel affecting the integrity of the material.

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Section: Resultsmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

A study on the damage evolution of P91 steel under cyclic loading at high temperature

Saad¹,

Bachok²,

Sun³

2016

Int. J. Automot. Mech. Eng.

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“…Microstructural evolution is faster under fatigue and creep-fatigue loading than under creep loading or isothermal annealing at high temperature. Fournier et al [2009] reported that the microstructural coarsening measured in relaxation fatigue and creep-fatigue tests at 550°C is comparable to that in creep tests above 600°C, but occurs much faster. Dislocation cell formation with decreased dislocation density, disappearance of low-angle boundaries, and carbide coarsening are suggested to be responsible for cyclic softening.…”

Section: Improved Bilinear Creep--fatigue Damage Model For G91 Steelmentioning

confidence: 93%

Status report on improved understanding of creep-fatigue damage in advanced materials.

Li¹,

Majumdar²,

Soppet³

et al. 2012

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This report provides an update on the materials performance criteria and methodology relevant to liquid metal reactors (LMRs), in particular, sodium cooled fast reactors. The report is the first deliverable (Level 3) in FY11 (M3A11AN04030303) under the work package A-11AN040303 "Materials Performance Criteria and Methodology" as part of Advanced Structural Materials Program for the Advanced Reactor Concepts.The overall objective of the Advanced Materials Performance Criteria and Methodology project is to evaluate the key requirements for the ASME Code qualification and the Nuclear Regulatory Commission (NRC) approval of advanced structural materials in support of the design and licensing of the liquid metal fast reactors. Advanced materials are a critical element in the development of fast reactor technologies. Enhanced materials performance not only improves safety margins and provides design flexibility but also is essential for the economics of future advanced fast reactors. Qualification and licensing of advanced materials are prominent needs for the development and implementation of advanced fast reactor technologies. Nuclear structural component designs in the U.S. comply with the ASME Boiler and Pressure Vessel (B&PV) Code Section III (Rules for Construction of Nuclear Facility Components) and the NRC grants licensing. As the LMR will operate at higher temperatures than the current light water reactors (LWRs), the design of elevated-temperature components must comply with ASME Section III Subsection NH (Class 1 Components in Elevated Temperature Service). A number of technical issues relevant to materials performance criteria and high temperature design methodology in the LMR were identified and presented in earlier reports [Natesan et al. 2008[Natesan et al. , 2009. A viable approach to resolve these issues and the R&D priority were also recommended. The development of mechanistically based creep-fatigue interaction models for life prediction and reliable data extrapolation was chosen to be the central focus in near-term efforts.Our current efforts focus on the creep-fatigue damage issue in high-strength ferriticmartensitic steels for two primary reasons. First, the current ASME design rule of bilinear damage summation puts severe limits of fatigue and creep loads for mod.9Cr-1Mo (G91) ferriticmartensitic steel, the lead structural material for fast reactors; secondly, the ferritic-martensitic steels behave fundamentally differently from austenitic stainless steels, for which the current ASME creep-fatigue design rules were developed. The unique deformation and damage characteristics in G91 steel, e.g. cyclic softening, degradation of creep and rupture strength during cyclic service, demands a new creep-fatigue design procedure that explicitly accounts for the material's unique creep-fatigue behavior. To support the development of predictive models and to resolve the over-conservative issue with the ASME design rule for G91 steel, we recovered stress relaxation data from thirteen creep-fatigue te...

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“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] In addition, the density of dislocations decreases. Recent studies [15,16,20,23,28,29] showed that these microstructural evolutions take place much faster under fatigue and CF compared to creep at the same temperature. These microstructural evolutions are the reason why the 9 to 12 pct Cr steels soften under cyclic loadings.…”

Section: Introductionmentioning

confidence: 99%

“…carried out at high temperature, in order to evaluate the effect of fatigue and CF on the creep behavior of 9 to 12 pct Cr steels. The second part of this study [29] is dedicated to the quantitative observations, at several scales, of the microstructural evolutions taking place under cyclic loadings. These two parts aim at highlighting the pronounced interactions that exist between creep and fatigue loadings.…”

Section: Introductionmentioning

confidence: 99%

Creep-Fatigue Interactions in a 9 Pct Cr-1 Pct Mo Martensitic Steel: Part I. Mechanical Test Results

Fournier

Sauzay

Caës

et al. 2008

Metall Mater Trans A

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Creep-fatigue (CF) tests are carried out on a modified 9 pct Cr-1 pct Mo (P91) steel at 550°C. These CF tests are strain controlled during the cyclic part of the stress-strain hysteresis loop and then load controlled when the stress is maintained at its maximum value, to produce a prescribed value of the creep strain before cyclic deformation is reversed under strain-controlled conditions. The observed cyclic softening implies that the applied creep stress continuously decreases with the number of cycles. However, the minimum creep rates measured at the end of the holding periods do not decrease when the applied stress decreases. The minimum creep rates measured at the end of these tests can be hundreds of times faster than those observed for the asreceived material. This acceleration of creep rates can be to the microstructural coarsening and to the decrease of the dislocation density observed after fatigue and CF loadings. Cyclic creep tests consisting of very long holding periods interrupted by unloading/reloading are also carried out. These results suggest that cyclic loadings affect the creep lifetime and flow behavior only if a plastic strain is applied during cycling. Creep tests carried out on a material cyclically prestrained and fatigue tests carried out on a material previously deformed in creep confirm that the deterioration of the mechanical properties is much faster in fatigue and CF compared to creep.

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Creep-Fatigue Interactions in a 9 Pct Cr-1 Pct Mo Martensitic Steel: Part II. Microstructural Evolutions

Cited by 92 publications

References 40 publications

A study on the damage evolution of P91 steel under cyclic loading at high temperature

A study on the damage evolution of P91 steel under cyclic loading at high temperature

Status report on improved understanding of creep-fatigue damage in advanced materials.

Creep-Fatigue Interactions in a 9 Pct Cr-1 Pct Mo Martensitic Steel: Part I. Mechanical Test Results

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