Creep Behaviour and Microstructural Changes of Advanced Creep Resistant Steels after Long-Term Isothermal Ageing

2010 ◽  
Vol 654-656 ◽  
pp. 504-507 ◽  
Author(s):  
Vàclav Sklenička ◽  
Květa Kuchařová ◽  
Milan Svoboda ◽  
A. Kroupa ◽  
J. Čmakal
Keyword(s):  
Rupture Strength ◽  
Creep Behaviour ◽  
Tensile Creep ◽  
Microstructural Stability ◽  
Creep Tests ◽  
Microstructural Changes ◽  
Creep Resistant Steels ◽  
Isothermal Ageing

In this paper we will try to further clarify the creep-strength degradation of selected advanced creep resistant steels. In order to accelerate some microstructural changes and thus to simulate degradation processes in long-term service, isothermal ageing at 650°C for 10000 h was applied to P91, P92 and P23 steels in their as-received states. The accelerated tensile creep tests were performed at temperature 600°C in argon atmosphere on all steels in the as-received state and after long-term isothermal ageing, in an effort to obtain a more complete description of the role of microstructural stability in high temperature creep of these steels. Creep tests were followed by microstructural investigations by means of both transmission and scanning electron microscopy and by the thermodynamic calculations. It is suggested that microstructural instability is the main detrimental process in the long-term degradation of the creep rupture strength of these steels.

scholarly journals Study on creep performance of launch canister under long-term storage

2019 ◽  
Vol 43 (2) ◽  
pp. 199-208 ◽  
Author(s):  
Cun-Gui Yu ◽  
Tong-Sheng Sun ◽  
Guang-Yuan Xiao
Keyword(s):  
Residual Deformation ◽  
Bottom Layer ◽  
Tensile Creep ◽  
Creep Model ◽  
Model Parameters ◽  
Creep Tests ◽  
Software Environment ◽  
Long Term Storage ◽  
Term Storage

In this paper, the creep performance of a multi-barrel rocket launch canister under long-term stacking storage is studied. Based on the Bailey–Norton model, a creep model for the frame material of a launch canister was established. Constant stress tensile creep tests under different stress levels at room temperature were carried out on the frame materials of the launch canister and the creep model parameters were obtained by test data fitting. The three-dimensional finite element model of the launch canister was established in the ABAQUS software environment and the creep deformation of the launch canister after long-term stacking storage was studied. The results indicated that the bottom layer of the launch canister frame presented an extended residual deformation when the stacking storage solution with the original support pad was used. Therefore, a position adjustment program of the support pad was put forward. The residual deformation of the launch canister frame after long-term storage could be significantly reduced, thus the performance requirements for the launch canister are guaranteed.

Prediction of long-term creep behaviour of Grade 91 steel at 873 K in the framework of microstructure-based creep damage mechanics approach

2018 ◽  
Vol 28 (6) ◽  
pp. 877-895 ◽  
Author(s):  
J Christopher ◽  
BK Choudhary
Keyword(s):  
Damage Mechanics ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Time Data ◽  
Grade 91 ◽  
Term Creep ◽  
Kinetic Creep ◽  
Grade 91 Steel

A detailed analysis has been performed for the prediction of long-term creep behaviour of tempered martensitic Grade 91 steel at 873 K using the microstructure-based creep damage mechanics approach. Necessary modifications have been made into the original kinetic creep law proposed by Dyson and McLean in order to account for the influence of microstructural damages arising from the coarsening of M23C6 and conversion of useful MX precipitates into deleterious Z-phase on creep behaviour of the steel. An exponential rate relationship has been introduced for the evolution of number density of MX precipitates with time. It has been shown that the developed model adequately predicts the experimental long-term creep strain–time as well as creep rate-time data. The role of Z-phase on long-term creep behaviour of Grade 91 steel has also been discussed.

Long Term Creep Life Prediction of New and Service Exposed P91 Steel

2018 ◽  
Author(s):  
Muneeb Ejaz ◽  
Norhaida Ab Razak ◽  
Andrew Morris ◽  
Scott Lockyer ◽  
Catrin M. Davies
Keyword(s):  
Tensile Strength ◽  
Creep Behaviour ◽  
Equivalent Stress ◽  
Practical Reasons ◽  
Creep Data ◽  
Short Term ◽  
Creep Tests ◽  
High Temperature Components ◽  
Term Creep

P91 steels are widely used in high temperature components for power generation. Creep data is often generated through accelerated short term creep tests, for practical reasons, via increasing stress or temperature though this may alter the creep behaviour. Through normalising the creep test stress by tensile strength the Wilshire models reduce the batch to batch scatter in the creep data and enable the prediction of long term creep data from relatively short term test results. In this work it is shown that the Wilshire models fitted to uniaxial creep rupture data can be used to predict failure in both as cast and service exposed multiaxial tests. This is provided that the equivalent stress is the rupture controlling stress, as is the case for the P91 tests examined, and the tensile strength is measured as part of the test programme.

A Reference Stress Approach to Creep Bending of Straight Tubes

1974 ◽  
Vol 16 (3) ◽  
pp. 125-138 ◽  
Author(s):  
J. Fairbairn
Keyword(s):  
Entire Range ◽  
Creep Behaviour ◽  
Tensile Creep ◽  
Bending Moments ◽  
Stress Distributions ◽  
Creep Tests ◽  
Reference Stress ◽  
Hyperbolic Sine ◽  
Rotation Method ◽  
Reference Stress Approach

Reference-stress parameters, based on the Norton constitutive equation, are developed for creep bending of circular and elliptical tubes. The parameters are presented in the form of a design chart. The reference stress methods apply also to other simple constitutive equations of the power law, exponential and hyperbolic sine forms, and also to two complex equations describing creep behaviour over the entire range from primary to tertiary. In these equations the functions of stress and time are not separable and reference stress techniques provide a convenient method of evaluating stationary stress distributions and investigating the variation of these stresses with time. Aluminium alloy tubes were creep tested with cyclic uniform bending moments. Creep strains to fracture were measured by an end-rotation method. The creep behaviour of the tubes was well predicted by reference-stress cyclic tensile creep tests.

Quantitative Evaluation of Secondary Phases in a Weld Joint Made of COST F and FB2 Creep Resistant Steels

2017 ◽  
Vol 270 ◽  
pp. 183-188
Author(s):  
Dagmar Jandová
Keyword(s):  
Quantitative Evaluation ◽  
Creep Strength ◽  
Weld Joint ◽  
Precipitate Size ◽  
Secondary Phases ◽  
Creep Tests ◽  
Transmission Electron ◽  
Creep Resistant Steels ◽  
Term Creep

Conventional (CCT) and accelerated (ACT) creep tests of a weld joint made of COST F and COST FB2 steels were carried out over a temperature range from 550 °C to 650 °C. Fracturing of the crept specimens was located in the heat affected zone (HAZ) of the F steel. Two specimens were selected after CCT and ACT for quantitative evaluation of the precipitates and compared to the weld joint in as-received conditions. Scanning and transmission electron micrographs were used to measure the precipitate size. Both methods were compared and the accuracy of the results was discussed. It was concluded that ACT can simulate the precipitation of chromium carbides and structure recovery during long term creep exposures. However, precipitation of Laves phase during CCT was not recorded after ACT. Therefore, it is difficult to use ACT in this experiment for estimating the long term creep strength.

Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe

2017 ◽  
Vol 270 ◽  
pp. 162-167
Author(s):  
Petr Král ◽  
Vaclav Sklenička ◽  
Květa Kuchařová ◽  
Marie Svobodová ◽  
Marie Kvapilová ◽  
...  
Keyword(s):  
Welded Joints ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Electron Back Scatter Diffraction ◽  
Steel Pipe ◽  
Tensile Creep ◽  
Creep Tests ◽  
P92 Steel ◽  
Welding Technology ◽  
Fracture Ductility

The microstructure and creep behaviour of the welded joints of P92 steel pipe were investigated in order to determine the influence of orbital heat welding technology on the creep resistance. Creep specimens were machined from the welded joints. Tensile creep tests of welded joints were performed at 873 K using different stresses. The microstructure of tested specimens was investigated by scanning electron microscope Tescan equipped with an electron-back scatter diffraction. The creep results showed that the creep fracture strain of the welded joints decreases with decreasing value of applied stress. Microstructure investigation showed that fracture behaviour of welded joints is influenced by an enhanced cavity formation at grain boundaries in the heat-affected zone causing lower fracture ductility.

Effect of Long-Term Aging and Creep Exposure on the Microstructure of TiAl-Based Alloy for Industrial Applications

2004 ◽  
Vol 842 ◽  
Author(s):  
Juraj Lapin ◽  
Mohamed Nazmy ◽  
Marc Staubli
Keyword(s):  
Chemical Composition ◽  
Constant Load ◽  
Industrial Applications ◽  
Tensile Creep ◽  
Creep Tests ◽  
Fine Needle ◽  
Term Creep ◽  
Applied Stresses ◽  
Creep Exposure

ABSTRACTThe effect of long-term aging and creep exposure on the microstructure of a cast TiAl-based alloy with nominal chemical composition Ti-46Al-2W-0.5Si (at.%) was studied. The aging experiments were performed at temperatures between 973 and 1073 K for various times ranging from 10 to 14000 h in air. Constant load tensile creep tests were performed at applied stresses ranging from 150 to 400 MPa and at temperatures between 973 and 1123 K up to 25677 h. During aging and creep testing the α2(Ti3Al)-phase in the lamellar and feathery regions transforms to the γ(TiAl)-phase and fine needle-like B2 precipitates. Microstructural instabilities lead to a softening of the alloy. The effect of this softening on long-term creep resistance is negligible at temperatures of 973 and 1023 K.

The Creep Behaviors of Two Fine-grained XD TiAl Alloys Produced by Similar Heat Treatments

2004 ◽  
Vol 842 ◽  
Author(s):  
Hanliang Zhu ◽  
Dongyi Seo ◽  
Kouichi Maruyama ◽  
Peter Au
Keyword(s):  
Grain Boundaries ◽  
Creep Resistance ◽  
Lamellar Spacing ◽  
Heat Treatments ◽  
Tensile Creep ◽  
Microstructural Stability ◽  
Creep Tests ◽  
Tial Alloys ◽  
Fine Grained ◽  
Interlocked Grain

ABSTRACTThe microstructural characteristics and creep behavior of two fine-grained XD TiAl alloys, Ti-45Al and 47Al–2Nb–2Mn+0.8vol%TiB2 (at%), were investigated. A nearly lamellar structure (NL) and two kinds of fully lamellar (FL) structures in both alloys were prepared by selected heat treatments. The results of microstructural examination and tensile creep tests indicate that the 45XD alloy with a NL structure possesses an inferior creep resistance due to its coarse lamellar spacing and larger amount of equiaxed γ grains at the grain boundaries, whereas the same alloy in a FL condition with fine lamellar spacing lowers the minimum creep rates. Contrary to 45XD, the 47XD alloy with a NL structure exhibits the best creep resistance. However, 47XD with a FL structure with finer lamellar spacing shows inferior creep resistance. On the basis of microstructural deformation characteristics, it is suggested that the well-interlocked grain boundary and relatively coarse colony size in FL and NL 47XD inhibit sliding and microstructural degradation at the grain boundaries during creep deformation, resulting in better creep resistance. Therefore, good microstructural stability is essential for improving the creep resistance of these alloys.

Influence of Microstructural Changes in Creep Resistant Steel after Long-Term Creep Tests on the Shape of the Polarization Curves

2015 ◽  
Vol 647 ◽  
pp. 153-161
Author(s):  
Jana Sladká ◽  
Dagmar Jandová ◽  
Eva Chvostová
Keyword(s):  
Martensitic Steel ◽  
Light And Electron Microscopy ◽  
Polarization Curves ◽  
Resistant Steel ◽  
Creep Tests ◽  
Microstructural Changes ◽  
Additional Peak ◽  
Term Creep ◽  
Non Destructive

Creep resistance of the steel depends on chemical and structural composition and structural stability. Therefore it is necessary to check microstructural changes in material during the long-term service, however the necessary material analyses are generally destructive. The submitted contribution describes non-destructive electrochemical method for detection of some microstructural changes taking place during creep exposures. The shape of polarization curves are correlated to the microstructure of CB2 steel, the most promissing (9-12) %Cr martensitic steel for the cast components. The dynamic polarization curves were measured using samples in as received conditions and after long-term creep tests at 650°C. Microstructure was analysed using light and electron microscopy. The microstructure of the CB2 steel changed during creep exposures. In polarization curves additional peak appeared in the main passivation region and the curve shape changed also in the secondary passivation region. The curve changed in dependence on precipitation and growth of Laves phase particles.

scholarly journals Oxidation of Ti–6Al–4V alloy between 450 and 600°C. Evolution of microstructure and mechanical properties

2020 ◽  
Vol 321 ◽  
pp. 06009
Author(s):  
Dominique Poquillon ◽  
Coralie Parrens ◽  
Alessandro Pugliara ◽  
Maxime Perrais ◽  
Benoit Malard
Keyword(s):  
Oxygen Uptake ◽  
Oxide Scale ◽  
Creep Behaviour ◽  
Oxygen Enrichment ◽  
Life Assessment ◽  
Creep Tests ◽  
Transmission Electron ◽  
Vibration Tests ◽  
Evolution Of Microstructure

Titanium alloys are widely used in many applications thanks to their good corrosion resistance and to their high specific modulus. However, at temperatures above 450°C, oxidation must be taken into account to improve life assessment of components. Especially for long-term exposures, oxidation leads to an oxide scale along with an oxygen enrichment in the metal below this oxide scale. In this study, the oxidation behaviour of Ti– 6Al–4V is investigated between 450 and 600°C for a maximum duration of about 6800 h. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) are used to characterize the oxide layer and the layer affected by oxygen uptake. The local oxygen content is quantified. Vibration tests are performed to determine elastic properties on thin specimens with different thicknesses affected by oxygen enrichment. Creep tests are also carried out to quantify the influence of this oxygen uptake on viscoplastic behaviour. An oxygen-enriched zone occupying 5% of the cross-section of a specimen is sufficient to induce detectable changes in its creep behaviour.

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