Creep Strength Evaluation Research Articles

Development of a creep testing machine with the maximum temperature 1000℃ for utilizing miniature specimens and evaluation of creep strength for IN713C-MIM

This paper presents the development of a creep testing machine with a maximum temperature 1000°C for utilizing miniature specimens and evaluation of creep strength for IN713C-MIM. The remaining life assessment of actual devices using the miniature specimens are expected as the better method because it can decrease the damage to them by sampling a specimen, so the test dates about miniature specimens are required. This study shows the developed testing machine and verification test results as well as some experimental results using IN713C-MIM. However, the MIM-materials creep strength is lower than the casting materials, although the experimental result are very few. This research aims at meeting the above needs and creating the superior heat-resistant alloy. The creep rupture time of IN713C-MIM and improvement of strength have been done by authors, but more detailed evaluating of the strength is also necessary. For this study, a suitable testing was required to evaluate creep strength more precisely.

Creep rupture properties and microstructures of 9Cr–3Co–3W-Nd-B steel welded joints

The creep rupture properties of welded joints and microstructures before and after creep rupture were evaluated for the 9Cr–3W–3Co-Nd-B steel, and simulated HAZ test was conducted to evaluate the creep strength and microstructures of HAZ. The creep strengths of welded joints were almost equivalent to the average strength of base metal, and the welded joints ruptured in HAZ in a similar manner as conventional steels in low-stress tests. The results of creep strength evaluation for simulated HAZ exhibited that welded joints of 9Cr–3W–3Co-Nd-B steel were the least strong in the areas heated to a temperature near 1050 °C, indicative of being the cause of HAZ rupture at the long-term region. A reduction in the creep strength was lessened at temperatures immediately above the AC3 transformation temperature, likely due to a combined effect of suppression of grain refinement by austenite memory effect and maintenance of the amount of grain boundary precipitates partly affected by large prior austenite grains.

Evaluation of Creep Strength in Small Turbine Wheels by using Very Small Punch Creep Specimen, and Relationship between Creep Strength and Microstructure

Evaluation of Creep Strength in Small Turbine Wheels by using Very Small Punch Creep Specimen, and Relationship between Creep Strength and Microstructure

Creep Strength Evaluation of Mod.9Cr-1Mo Steel Welded Joint by Using Miniature Specimens.

Creep Strength Evaluation of Mod.9Cr-1Mo Steel Welded Joint by Using Miniature Specimens.

Creep Strength Evaluation of a Long-Term Used Boiler Weldment Part on 2.25Cr-1Mo Steel by Using Miniature Specimens

Creep Strength Evaluation of a Long-Term Used Boiler Weldment Part on 2.25Cr-1Mo Steel by Using Miniature Specimens

Shortening the Long Creep Strength Evaluation Period with the Assistant of Stress Relaxation Behavior

P92 heat-resistant steel was used to demonstrate that creep rupture life evaluation period could be shorted by the assistant of the creep data from short-period stress relaxation test without reducing the prediction precision. Research showed that the minimum creep rate and the relaxation creep rate were exchangeable, and the stress exponent and the apparent activation energy analysis of the constant strain creep and the constant stress creep showed a similar deformation mechanism at the condition of T and . The creep rupture life predicted through the combination of these two kinds of creep data was closer to the real creep data than that evaluated by the traditional method based on the time to rupture only, and the precision of the evaluated creep strength increased at last 14.5 %.

Evaluation of Creep Strength of Heterogeneous Welded Joint in HR6W Alloy and Sanicro 25 Steel

AbstractThis article presents the results of investigations on HR6W alloy and Sanicro 25 steel and the dissimilar welded joint made of them. The characteristic images of microstructure of the investigated materials in the as-received condition and following the creep test, observed with a scanning electron microscope (SEM), are shown. The X-ray analysis of phase composition of the existing precipitates was carried out. The method for evaluation of creep strength based on abridged creep tests carried out at a temperature higher than the design one is presented. The obtained results do not deviate from the values of creep strength determined in long-term creep tests. The maximum difference in creep strength of the investigated materials is ±20%, which is in compliance with the acceptable scatter band. The methodology presented can be used for verification of creep strength (life time) of the material of finished components to be operated under creep conditions.

Comparison of creep strength and intrinsic ductility for serviced and reheat treated T91 steel based on stress relaxation testing

High precision stress relaxation tests (SRT) at four temperatures were conducted on T91 (9%Cr) steel after extended boiler service, and also after re-heat treatment. Relative differences in creep strength, measured over five decades in strain rate were dependent on test temperature. Using an established correlation between strain rate sensitivity and elongation at failure, intrinsic ductility values as a function of stress and test temperature were determined. The general trend of a minimum in ductility in terms of stress or strain rate was consistent with long term creep rupture data on T91, and with literature data on alloy steels. However, the precision and repeatability of the SRT analysis contrasted with the appreciable scatter and heat to heat variation in traditional testing. It is argued that the current creep strength evaluation based on the nearly constant state measurement from the SRT test is superior to the measurement of stress dependence of minimum creep rate in traditional creep rupture testing. The complexity of primary creep in laboratory testing, which may not be significant at operating stresses where loading strains may be fully recoverable (anelastic), does not apply to the SRT. Since very low strain rates are achieved in a one day test, the procedures for setting of design allowables and design analysis based on the SRT data should not be significantly different from current practice. This technique offers accelerated alloy development and optimisation for creep strength and also ductility, and hence resistance to notch sensitivity.

Creep Strength Evaluation of Long Term Used Boiler Welded Joint on Mod. 9Cr-1Mo Steel by Using a Miniature Specimen.

Creep Strength Evaluation of Long Term Used Boiler Welded Joint on Mod. 9Cr-1Mo Steel by Using a Miniature Specimen.

ミニチュア試験片を用いた長期使用改良9Cr-1Mo鋼ボイラ溶接部のクリープ強度評価

ミニチュア試験片を用いた長期使用改良9Cr-1Mo鋼ボイラ溶接部のクリープ強度評価

Application of stress relaxation testing in evaluation of creep strength of a tungsten-alloyed 10% Cr cast steel

Uniaxial isothermal stress relaxation tests (SRT) were performed on a tungsten-alloyed 10% Cr cast steel (G-X12Cr Mo W V Nb N 10 1 1) at temperatures of 580, 600 and 620 °C and initial strain levels of 0.2, 0.5 and 0.8%. Inelastic strain rates for different stresses were estimated from the stress versus time data generated from the tests. Conventional creep tests were also conducted on the same material at 580, 600 and 620 °C and at different stress levels. The strain rate data estimated from SRT were compared with minimum creep rates derived from the creep tests; the strain rates estimated from SRT with 0.8% initial strain level are in better agreement than those estimated from SRT with 0.2 and 0.5% initial strain levels. In order to ascertain the technique, stress relaxation behaviour was estimated from creep test data and compared with the stress relaxation curves obtained from SRT at corresponding temperatures. The stress relaxation curves obtained from SRT with 0.8% initial strain level are in good agreement with the stress relaxation curves estimated from the creep tests. It is concluded that the stress relaxation test with initial strain level of 0.8% could be considered as an appropriate short-term test technique for estimation of creep strength of newly developed materials.

Evaluation of Creep Strength and Damage of Gr.122 Steel Welded Joint

11Cr-0.4Mo-2W-CuVNb steel (ASME Gr.122) has been used for boiler components in ultra-supercritical (USC) thermal power plants. Creep strength of high Cr steel welds decreases due to the formation of Type-IV creep damage in heat-affected zone (HAZ) during long-term use at high temperatures. In the present paper, the creep strength and microstructures of simulated HAZs and a welded joint of Gr.122 steel were investigated. In order to elucidate the processes of Type-IV creep damage, creep tests using thick welded joint specimens were interrupted at several time steps, and the initiation, evolution and distribution of creep voids were measured. It was found that Type-IV creep voids grew after 0.5 of life and a crack formed after 0.9 of life. Creep damage was observed mostly at 1/3 below the surface of the plate. Differences of the Type-IV damage processes between Gr.91 and Gr.122 steel weld were discussed. Experimental creep damage distributions were compared with computed versions using finite element method and damage mechanics analysis.

J031033 はんだBGA ボールを用いた微小接合部クリープ強度評価([J03103]電子情報機器,電子デバイスの強度・信頼性評価と熱制御(3))

J031033 はんだBGA ボールを用いた微小接合部クリープ強度評価([J03103]電子情報機器,電子デバイスの強度・信頼性評価と熱制御(3))

Effect of stress on the creep deformation of ASME Grade P92/T92 steels

Abstract The stress versus strain curve of ASME Grade P92/T92 steels was analysed and the stress dependence of the creep deformation behavior was investigated. Good correspondence between 50% of 0.2% offset yield stress and a proportional limit was observed over a range of temperatures from 550 to 700°C. Stress dependence of the minimum creep rate was divided into two groups of high and low stress regimes with a boundary condition of 0% offset yield stress. Creep deformation in the low stress regime was considered to be controlled by dislocation climb. Large stress dependence of the minimum creep rate in the high stress regime was equivalent to the strain rate dependence of flow stress observed in the tensile test. Creep strength in the high stress regime is assumed to be influenced by plastic deformation, and should be excluded for a long-term creep strength evaluation.

Creep and Fatigue at Elevated Temperatures. Advances in the Use of Stress Relaxation Data for Design and Life Assessment in Combustion Turbines.

This paper describes developments in the use of the high-precision stress relaxation test (SRT) as a basis for accelerated creep strength evaluation. In tests lasting less than one day a creep rate range of about five decades may be covered. It is shown how the approach is especially useful for superalloys and their application in combustion turbines. Using creep rate data, derived from the SRT tests, for conventionally cast, directionally aligned and monocrystalline alloys, a new framework for design and life management is described. By parameterizing the results over a range of temperature it is possible to attain design stress levels in less than a week of testing. The test may be used to determine the effect of microstructural features such as grain size and grain orientation, thermal--mechanical exposure conditions, test specimen section size, and the effect of location within a component.

Stress Relaxation Testing of Service Exposed IN738 for Creep Strength Evaluation

Standard size and miniature specimens of IN738 were taken from a service exposed turbine blade and vane for comparative stress relaxation testing at 800C, 850C, and 900C. Base data taken from root section material were used to construct stress versus creep rate parametric curves which could be used directly in design. Up to five decades in creep rates were obtained at each temperature from tests lasting less than one day. The data were also presented in the form of stress versus predicted times to 0.5 percent creep which compared well with available long time creep data. Differences were noted in specimens taken from different locations in the airfoil regions which probably resulted from differences in grain size or orientation. Based on these measurements it was concluded that there was no significant effect of section size on creep strength as defined by this test, and that the alloy was quite insensitive to prior deformation and thermal exposures. A life management procedure, using a combination of creep strength evaluation based on the stress relaxation test and a separate fracture evaluation measurement, is outlined in which end of useful life is defined in terms of minimum acceptable performance levels. [S0742-4795(00)01803-2]

ＦＢＲ用溶接継手の高温低サイクル疲労，クリープ及びクリープ疲労強度評価例

To establish an evaluation method of elevated temperature strength for weldments, a series of investigations1)-5) had been performed on the low-cycle fatigue strength. In this study, the suitable evaluation methods of creep and creep-fatigue strengths for weldments were proposed and were applied to the life prediction of FBR weldments.The following results were obtained.(1) In the evaluation of low-cycle fatigue strength for the weldments, the accuracy of life prediction by the Method (I), Method (II) and FEM was determined mainly by the difference in cyclic deformation resistance between the base metal and the weld metal. The Method (I), Method (II) and FEM were effective for the weldments which have small difference in cyclic deformation resistance such as stainless steel and 21/4 Cr-1 Mo steel with PWHT. But for the weldments which have large difference in cyclic deformation resistance such as the 21/4 Cr-1 Mo steel without PWHT, the Method (I) predicted the life overconservatively and FEM overestimated the life inversely.(2) In the evaluation of creep strength for the weldments, the minimum creep strain rate of the 21/4 Cr-1 Mo steel weldment was predicted by the Independent Method which paid attention to only the weakest part of the weldment and also by the Interaction Method which considered the interaction between the base metal and the weld metal. Both of them were found to be effective for the 21/4 Cr-1 Mo steel weldments.(3) In the evaluation of creep-fatigue strength for the weldments, a new method was proposed which was an extension of the fatigue evaluation method (I) based on the linear damage summation rule. It could predict the life of the 21/4 Cr-1 Mo steel weldments within a factor of two on life.