Creep Rupture Properties Research Articles

Influence of Aging on Creep Rupture Properties of Heat Resistant Steels for Steam Turbine Rotors of Thermal Power Plants

Influences of aging on the creep rupture properties of super-clean 9%CrMoV steel and 1%CrMoV steel, the heat resistant steels for steam turbine rotors of thermal power plants, are investigated. Using the as-received and the aging-treated materials of the two steels, creep rupture tests are carried out at 566°C. Creep rupture lives, creep fracture modes as well as the microstructural changes of the specimens are examined. It is made clear that the creep strength and the microstructural stability of super-clean 9%CrMoV steel are superior to those of 1%CrMoV steel in long-term services.

On Electro Discharge Machining of Inconel 718 with Hollow Tool

Inconel 718 is a nickel-based alloy designed for high yield, tensile, and creep-rupture properties. This alloy has been widely used in jet engines and high-speed airframe parts in aeronautic application. In this study, electric discharge machining (EDM) process was used for machining commercially available Inconel 718. A copper electrode with 99.9% purity having tubular cross section was employed to machine holes of 20 mm height and 12 mm diameter on Inconel 718 workpieces. Experiments were planned using response surface methodology (RSM). Effects of five major process parameters—pulse current, duty factor, sensitivity control, gap control, and flushing pressure on the process responses—material removal rate (MRR) and surface roughness (SR) have been discussed. Mathematical models for MRR and SR have been developed using analysis of variance. Influences of process parameters on tool wear and tool geometry have been presented with the help of scanning electron microscope (SEM) micrographs. Analysis shows significant interaction effect of pulse current and duty factor on MRR yielding a wide range from 14.4 to 22.6 mm3/min, while pulse current remains the most contributing factor with approximate changes in the MRR and SR of 48 and 37%, respectively, corresponding to the extreme values considered. Interactions of duty factor and flushing pressure yield a minimum surface roughness of 6.2 μm. The thickness of the sputtered layer and the crack length were found to be functions of pulse current. The hollow tool gets worn out on both the outer and the inner edges owing to spark erosion as well as abrasion due to flow of debris.

Reliability Design for Creep Rupture Strength of 2.25Cr-1Mo Steel

A statistical analysis of creep rupture data for 2.25Cr-1Mo steel was performed. The scattering of creep rupture data was represented by Z-parameter method based on Manson-Haferd method. With the application of Z-parameter, reliability design for allowable stress of creep rupture strength was carried out according to design life. The higher the value of confidence level, the lower the allowable stress. In comparison with safety factor method and minimum rupture strength method, it can be seen that reliability design based on Z-parameter is more agree with experimental data than other methods. Reliability design provides more precise results by considering the real distribution of creep rupture property and provides more flexible choice for design due to the need of safety and economy.

Helium transport, fate and management in nanostructured ferritic alloys: In situ helium implanter studies

High helium levels produced in fusion neutron spectra may lead to severe increases in the brittle fast fracture temperature, enhanced void swelling and degradation of creep rupture properties at lower, intermediate and higher irradiation temperatures, respectively. Thus it is important to develop structural alloys with stable microstructures that can manage helium based on understanding of its transport, fate and consequences. We report on the initial results of a study of helium in a nanostructured ferritic alloy (NFA), MA957, that is dispersion strengthened by an ultra-high density of nm-scale Y–Ti–O nanofeatures (NFs). An in situ helium implanter technique uniformly deposited ≈380appm helium to ≈6μm in MA957 irradiated in the High Flux Isotope Reactor (HFIR) to ≈9 dpa at 500°C. Through focus transmission electron microscopy (TEM) showed that helium is in extremely fine bubbles that often appear to coincide with bright field features taken as a NF.

Anisotropie Creep Rupture Properties of a Nickel-base Single Crystal Superalloy at High Temperature

The creep rupture properties of a single crystal superalloy were tested at 975°C/255 MPa as a function of the deviation degrees from [001]. The misorientation of the specimens away from [001] distributed approximately along a line between [001]–[011] and [001]–[111] boundaries in the triangle of the stereographic projection. Creep rupture lifetimes of the specimens were not sensitive to the misorientation until the deviation degree exceeded ∼30 deg. Two steps of lattice rotation were found in all specimens during creep, first towards the [001]–[111] boundary, and then to [001] or [111] along the boundary. Single slip and strong asymmetric deformation were observed during the first stage of lattice rotation in specimens with large misorientation. The rotation mechanism was associated with the activated slip systems according to the calculated Schmid factors. The impact of lattice rotation on the rupture properties was also discussed.

Assessment of creep rupture properties for dissimilar steels welded joints between T92 and HR3C

Dissimilar steels welded joints, between ferritic steel and austenitic stainless steel, are always encountered in high-temperature components in power plants. As two new grade ferritic steel and austenitic stainless steel, T92 (9Cr0.5Mo2WVNb) and HR3C (TP310HCbN), exhibit superior heat strength at elevated temperatures and are increas- ingly applied in ultra-supercritical (USC) plants around the world, a complete assessment of the properties for T92/HR3C dissimilar steels welded joints is urgently required. In this paper, metallographic microstructures across the joint were inspected by optical mi- croscope. Particularly, the creep rupture test was conducted on joints under different load stresses at 625 ◦ C to analyse creep strength and predict their service lives, while their fractograph were observed under scanning electron microscope. Additionally, finite element method was employed to investigate residual stress distribution of joints. Results showed that the joints were qualified under USC conditions, and T92 base material was commonly the weakest part of them.

Creep Rupture Properties and fracture type of 9Cr-1Mo-V-Nb/18Cr-8Ni steel dissimilar joints

By conducting long-term creep rupture tests for dissimilar weld joints (9Cr-1Mo-V-Nb/18Cr-8Ni) made with Gas Tungsten Arc Welding (GTAW) and Friction Joining (FJ), creep rupture properties and microstructures were examined, and the relationships between changes in microstructure and nucleation and propagation of creep cracks that occur during creep deformation in weld joint specimens were studied. Creep rupture tests of GTAW joints were conducted at three temperatures: 550, 600 and 650 °C, under applied stresses of 160–240 MPa, 80–160 MPa and 40–80 MPa, respectively. Creep rupture tests of FJ joints were conducted at 600 °C and 650 °C under stresses ranging from 40 to 160 MPa and 30 to 80 MPa, respectively. The creep-rupture strength of dissimilar weld joint specimens was lower than that of the 9Cr-1Mo-V-Nb base metal specimen at all temperature levels. In addition, the differences in creep strength between the dissimilar weld joint specimen and the base metal specimen tended to be greater at higher temperature levels. The fracture type of dissimilar weld joint was transformed from a Type V fracture and a Type VII fracture mode to a Type IV fracture mode following long-term creep rupture tests. The fracture type of the dissimilar weld joints was predicted as a Type IV fracture mode at 550 °C and 600 °C and with rupture occurring after 100 000 hours.

Obtaining confidence limits for safe creep life in the presence of multi batch hierarchical databases: An application to 18Cr–12Ni–Mo steel

The creep and creep rupture properties of 18Cr–12Ni–Mo steel tubes have been analysed using the Wilshire equations. The observed behaviour patterns are then briefly discussed in terms of the dislocation processes governing creep strain accumulation. A suitable statistical framework for analysing both the single and multi batch data available on this material is then specified. It is shown that ignoring the hierarchical nature present in many creep data bases, which has been the approach used until now when using the Wilshire equations, leads to a serious and significant underestimate of the predicted safe life for this material. The model allows accurate predictions, with associated levels of confidence, of long-term properties by extrapolation of short-term test results for this steel.

PROCESSING, MICROSTRUCTURE AND MECHANICAL PROPERTIES OF LARGE DIRECTIONALLY SOLIDIFIED CASTINGS FOR INDUSTRIAL GAS TURBINE APPLICATIONS

Contamination of low melting point metal and distortion and fracture of ceramic shell during directional solidification assisted by liquid metal cooling(LMC) were discussed.Large DS castings with 430 mm in length were produced by optimizing the processing parameters.The microstructure,heat treatment response and typical creep rupture properties of the large casting were analyzed.Results of the preliminary casting trials of large blades were also reported.

Application of Manson–Haferd and Larson–Miller Methods in Creep Rupture Property Evaluation of Heat-Resistant Steels

The current paper discusses the selection of Manson–Haferd and Larson–Miller constants on correlation results of creep rupture property in several heat-resistant steels. It indicates that the change in Larson–Miller constant CLM has obvious effect on the predicting result of rupture life and the optimal CLM values will depend on materials and the optimal ranges of the values are narrow. However, for Manson–Haferd constants Ta and log ta, they are at least phenomenally not independent variables but show a linear relationship: log ta=27.015−0.0267Ta. It is shown that the values of Manson–Haferd constants (Ta,log ta) can be selected in a wide range with desirable correlation accuracy and a set of Manson–Haferd constant (Ta=450, log ta=15) is recommended to correlate the creep rupture data.

A New Approach of Reliability Design For Creep Rupture Property

Generally, creep rupture data of a heat-resistant steel can be compressed into a narrow band by using a temperature-time parametric method such as the Larson–Miller or Manson–Haferd method. In order to describe the scattering of the data, the current paper proposes a “Z parameter” method to represent the magnitude of the deviation of the rupture data to master curve. Statistical analysis shows that the scattering of the Z parameter for several types of steels is supported by normal distribution. Using this method, it is possible to achieve unified analysis of the creep rupture data in various temperature and stress conditions. Stress-time temperature parameter-reliability curves (σ-TTP-R curves), stress-rupture time-reliability curves (σ-tr-R curves), and allowable stress-temperature-reliability curves ([σ]-T-R curves) are proposed, which could embrace the reliability concept into creep rupture property design.

A multi-level model for the analysis and prediction of creep and creep fracture of 2.25Cr–1Mo steel tubes

The creep and creep rupture properties of 2.25Cr–1Mo steel tubes have been analysed using the Wilshire equations. The observed behaviour patterns are then discussed in terms of the dislocation processes governing creep strain accumulation. A suitable statistical framework for analysing both the single and multi batch data available on this material is then specified. It is shown that ignoring the hierarchical nature present in many creep data bases, which has been the approach until now when using the Wilshire equations, leads to a serious and significant underestimate of the predicted safe life for this material. The model allows accurate predictions of long-term properties by extrapolation of short-term results for this steel.

Effect of surface recrystallization on the creep rupture property of a single-crystal superalloy

The effect of surface recrystallization by heating after shot-peening on the creep rupture property and fracture behavior of a single-crystal superalloy was investigated. The results show that the creep rupture property of the single-crystal superalloy was greatly influenced by surface recrystallization. A recrystallized surface layer with a depth of 101 μm resulted in a decrease in creep rupture life by nearly 50%, and an almost linear reduction of creep rupture life was observed with the increase of recrystallization depth. A lower strength of the recrystallized layer, inhomogeneous deformation between the recrystallized layer and the matrix, and stress concentration caused by notch effect resulted in the decrease in creep rupture life of the single-crystal superalloy.

On the role of μ phase during high temperature creep of a second generation directionally solidified superalloy

The role of μ phase in a second generation directionally solidified Ni-base superalloy during high temperature creep has been characterized in the present work. A large amount of blocky μ phase enveloped by thick γ′-film is found at the grain boundaries and in the vicinity of primary MC carbides after heat treatment. However, the creep-rupture properties of the alloy are not affected by the presence of the blocky μ phase at 760–1070 °C under a stress of 120–850 MPa. By the investigation of creep microstructure at 975 °C/255 MPa, it is found that the thick γ′-film plays a pivotal role in toughening the grain boundaries and the interfaces between the μ phase (or carbides) particles and the matrix, and preventing the formation of cracks. Meanwhile, during high temperature creep, M 23C 6 carbides are continuously coarsening with the dissolution of the μ phase particles and MC carbides, especially at the grain boundaries. The poor interface cohesion strength between such large M 23C 6 carbides and the γ matrix at the vertical segments of the directionally solidified grain boundaries leads to the final creep failure of the present alloy.

Effect of surface recrystallization on the creep rupture properties of a nickel-base single crystal superalloy

The effect of recrystallization on the creep rupture properties of a nickel-base single crystal superalloy has been investigated. It has been found the creep rupture life decreases with increasing of recrystallized depth in the alloy deformed by shot peening. A number of secondary cracks, which link each other and separate the recrystallized region and the matrix, have been observed in the recrystallized alloy after creep rupture. Coarse γ′ precipitations have been found in the interface between the recrystallized grain boundary and the matrix. It pins the crack propagation along the recrystallized grain boundary. Twinning boundary, more stable than high angle grain boundary, is difficult to crack.

The effect of heat treatments on the creep–rupture properties of a wrought Ni–Cr heat-resistant alloy at 973 K

The effect of heat treatments on the creep–rupture properties was investigated on a wrought Ni–Cr heat-resistant alloy at 973 K. Short-time aging (aging for 3.6 ks (1 h) at 973 K) was made on the solution-treated specimens with different grain sizes. The fine-grained specimen (the grain diameter, d = 45.2 μm) produced by short-time solution treatment exhibited almost the same rupture life and superior creep ductility as those of the medium-grained specimen (d = 108 μm) produced by normal solution treatment. The fine-grained specimen and medium-grained specimen showed the longer rupture life compared with the specimen with recommended aging. The principal strengthening of specimens was attributed to the precipitation hardening by γ′ phase particles. The fine-grained specimen had the highest hardness, and the increase of the hardness was observed in both the fine-grained and the medium-grained specimens during creep at 973 K. However, coarse-grained specimen (d = 286 μm) with high-temperature long-time solution treatment exhibited significantly short rupture life owing to insufficient precipitation hardening after the short-time aging and during creep. Ductile intergranular fracture with dimples occurred in the fine-grained specimen, while brittle intergranular fracture was observed in the medium-grained specimen and in the specimen with recommended aging. Both transgranular fracture and brittle intergranular fracture were observed in the coarse-grained specimen. A simple heat treatment composed of short-time solution treatment and short-time aging is applicable to high-temperature components of wrought Ni–Cr alloys.

Creep and creep fracture of 2.25Cr–1.6W steels (Grade 23)

The creep and creep rupture properties of Grade 23 (2.25Cr–1.6W) steels have been analysed for material produced in pipe (P23) and tube (T23) forms. The similarities and differences in the behaviour patterns observed for the pipe and tube products are then discussed in terms of the dislocation processes governing creep strain accumulation and the various damage phenomena causing the onset of tertiary creep and eventual fracture. Finally, the stresses causing failure of these materials in 100,000h at different temperatures are estimated to provide design data for construction of future power plant.

Creep properties and microstructural evolution of austenitic TEMPALOY steels

The steam parameters in the new high efficiency fossil fuel power plants are continuously increasing, requiring new advanced materials with enhanced creep strength able to operate on the most severe temperature and pressure conditions. For super-heater and re-heater applications, TEMPALOY AA-1 steel, an evolution of 18Cr10NiNbTi alloy, has been developed through the addition of 3%Cu and B, significantly enhancing the creep resistance, while offering typical corrosion properties of 18%Cr steels. This paper describes Tenaris’ tubular products in the field of austenitic grades for applications in Ultra Super Critical power plants: the production route and the main microstructural and mechanical properties of TEMPALOY AA-1 and TEMPALOY A-3 steels, including the effect of shot blasting on steam-oxidation resistance, their creep–rupture properties and their microstructural evolution during temperature exposure are presented.

KUBOTA ALLOY HN

Abstract Kubota alloy HN is an austenitic Fe-Ni-Cr alloy with long-term creep-rupture properties that are intermediate between those of HK40 and HP40 alloys. Carburization resistance is better than that of HK40, but oxidation resistance is generally lower, making the alloy suitable for long service at 1095 deg C (2000 deg F). This datasheet provides information on composition, physical properties, and tensile properties as well as creep. It also includes information on high temperature performance and corrosion resistance as well as casting, machining, and joining. Filing Code: SS-1060. Producer or source: Kubota Metal Corporation, Fahramet Division.

The effect of heat treatment on mechanical properties of in situ synthesized 7715D titanium matrix composites

7715D titanium matrix composites (TMCs) reinforced with TiB, TiC and La 2O 3 were in situ synthesized by common casting and hot-forging technology. Two kinds of heat treatments were adopted. Fully lamellar microstructures and equiaxed microstructures were obtained by annealing in β and α + β phases, respectively. The tensile properties of the composites at both ambient and elevated temperatures and also the creep rupture properties were tested. The TMCs with fully lamellar microstructures show superior comprehensive properties in comparison with those with equiaxed microstructures. Lamellar microstructure retarded the crack propagation which originated from cracked whisker more effectively. The strengthening effect of reinforcements can be given full play for the composites with lamellar microstructures.