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Creep resistance
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Proceedings Papers
AM-EPRI2024, Advances in Materials, Manufacturing, and Repair for Power Plants: Proceedings from the Tenth International Conference, 147-158, October 15–18, 2024,
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Increasing the temperature capabilities of ferritic/martensitic 9-12% Cr steels can help in increasing the operating temperature of land-based turbines and minimize the use of expensive high-temperature alloys in the hot section. A creep resistant martensitic steel, JMP, was developed with the potential to operate at or above 650°C. The design of the alloys originated from computational modeling for phase stability and precipitate strengthening using fifteen constituent elements. Cobalt was used for increased solid solution strengthening, Si for oxidation resistance and different W and Mo concentrations for matrix strength and stability. The JMP steels showed increases in creep life compared to MARBN/SAVE12AD at 650°C for testing at various stresses between 138 MPa and 207 MPa. On a Larson-Miller plot, the performance of the JMP steels surpasses that of state-of-the-art MARBN steel. Approximately 21 years of cumulative creep data are reported for the JMP steels which encompasses various compositions. The relationships between composition-microstructure-creep properties are discussed including characterization of microstructures after >20,000 hours in creep.
Proceedings Papers
AM-EPRI2024, Advances in Materials, Manufacturing, and Repair for Power Plants: Proceedings from the Tenth International Conference, 195-206, October 15–18, 2024,
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In order to enable safe long-term operation, metallic pipes operated in the creep range at high temperatures require considerable wall thicknesses at significant operating pressures, such as those required in thermal power plants of all kinds or in the chemical industry. This paper presents a concept that makes it possible to design such pipes with thinner wall thicknesses. This is achieved by adding a jacket made of a ceramic matrix composite material to the pipe. The high creep resistance of the jacket makes it possible to considerably extend the service life of thin- walled pipes in the creep range. This is demonstrated in the present paper using hollow cylinder specimens. These specimens are not only investigated experimentally but also numerically and are further analyzed after failure. The investigations of the specimen show that the modeling approaches taken are feasible to describe the long-term behavior of the specimen sufficiently. Furthermore, the paper also demonstrates the possibility of applying the concept to pipeline components of real size in a power plant and shows that the used modeling approaches are also feasible to describe their long-term behavior.
Proceedings Papers
AM-EPRI2024, Advances in Materials, Manufacturing, and Repair for Power Plants: Proceedings from the Tenth International Conference, 259-269, October 15–18, 2024,
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Gas turbine blades made from nickel-based superalloys, valued for their high temperature stability and creep resistance, undergo various forms of microstructural degradation during extended service at elevated temperatures that can ultimately lead to blade failure. To extend blade and turbine rotor life, Sulzer has developed evaluation and rejuvenation processes that include microstructural assessment and stress rupture testing of specimens from service-exposed blades. While stress rupture testing presents certain limitations and challenges in evaluating material condition, Sulzer has successfully rejuvenated hundreds of gas turbine blade sets across multiple superalloy types, including GTD 111, IN 738 LC, and U 500, demonstrating the effectiveness of heat treatment rejuvenation in improving microstructure and mechanical properties of service-degraded components.
Proceedings Papers
AM-EPRI2024, Advances in Materials, Manufacturing, and Repair for Power Plants: Proceedings from the Tenth International Conference, 592-599, October 15–18, 2024,
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The aspiration to deploy Nb-based alloys as viable upgrade for Ni-based superalloys is rooted in their potential for superior performance in high-temperature applications, such as rocket nozzles and next-generation turbines. However, realizing this goal requires overcoming formidable design hurdles, including achieving high specific strength, creep resistance, fatigue, and oxidation resistance at elevated temperatures, while preserving ductility at lower temperatures. Additionally, the requisite for alloy bond-coatings, to ensure compatibility with coating materials, further complicates the design process. QuesTek Innovations has its Integrated Computational Materials Engineering (ICME) technologies to design a superior performance high-temperature Nb-based superalloy based on solid solution and precipitation strengthening. Additionally, utilizing a statistical learning method from very limited available data, QuesTek engineers were able to establish physics-based material property models, enabling accurate predictions of equilibrium phase fraction, DBTT, and creep properties for multicomponent Nb alloys. With the proven Materials by Design methodology under the ICME framework, QuesTek successfully designed a novel Nb superalloy that met the stringent design requirements using its advanced ICMD materials modeling and design platform.
Proceedings Papers
AM-EPRI2024, Advances in Materials, Manufacturing, and Repair for Power Plants: Proceedings from the Tenth International Conference, 861-872, October 15–18, 2024,
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The advancement of additive manufacturing (AM) technology has heightened interest in producing components from nickel-based superalloys for high-temperature applications; however, developing high gamma prime (γ’) strengthened alloys suitable for AM at temperatures of 1000°C or higher poses significant challenges due to their “non-weldable” nature. Traditional compositions intended for casting or wrought processes are often unsuitable for AM due to their rapid heating and cooling cycles, leading to performance compromises. This study introduces ABD-1000AM, a novel high gamma prime Ni-based superalloy designed using the Alloys-by-Design computational approach to excel in AM applications at elevated temperatures. Tailored for AM, particularly powder bed fusion, ABD-1000AM demonstrates exceptional processing capability and high-temperature mechanical and environmental performance at 1000°C. The study discusses the alloy design approach, highlighting the optimization of key performance parameters, composition, and process-microstructure-performance relationships to achieve ABD-1000AM’s unique combination of processability and creep resistance. Insights from ABD-1000AM’s development inform future directions for superalloy development in complex AM components.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 60-70, October 21–24, 2019,
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Development of steels used in the power generation industry for the production of boilers characterized by supercritical parameters poses new challenges. The introduction of new combinations of alloying agents aimed at obtaining the best possible mechanical properties, including creep resistance, affects the weldability of new steels. Each of the latter has to undergo many tests, particularly as regards bending and welding, in order to enable the development of technologies ensuring failure-free production and assembly of boiler systems. Martensitic steels containing 9% Cr, used in the manufacturing of steam superheaters, are characterized by excellent creep resistance and, at the same time, low oxidation resistance at a temperature in excess of 600°C. In turn, steels with a 12% Cr content, i.e., VM12-SHC or X20CrMoV12-1 are characterized by significantly higher oxidation resistance but accompanied by lower strength at higher temperatures, which translates to their limited application in the production of boilers operating at the most top parameters.X20CrMoV12-1 was withdrawn from most of the power plants, and VM12-SHC was supposed to replace it, but unfortunately, it failed in regards to creep properties. To fulfill the gap a new creep strength-enhanced ferritic steel for service in supercritical and ultra-supercritical boiler applications was developed by Tenaris and it is designated as Thor115 (Tenaris High Oxidation Resistance). This paper covers the experience gained during the first steps of fabrication, which includes cold bending and welding of homogenous joints.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 360-369, October 21–24, 2019,
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This work deals with the potential of microstructurally based modeling of the creep deformation of martensitic steels. The motivation for the work stems from the ever increasing demand for higher efficiency and better reliability of modern thermal power plants. Service temperatures of 600°C and stress levels up to 100 MPa are currently the typical requirements on critical components. High creep and oxidation resistance are the main challenges for a lifetime 10+ years in steam atmosphere. New materials may fulfill these requirements; however, the save prediction of the creep resistance is a difficult challenge. The model presented in this work takes into consideration the initial microstructure of the material, its evolution during thermal and mechanical exposure and the link between microstructural evolution and creep deformation rate. The model includes the interaction between the relevant microstructural constituents such as precipitates, grain- lath- and subgrain boundaries and dislocations. In addition, the material damage is included into the model. The applicability of the model is then demonstrated on standard creep resistant alloys. Contrary to phenomenological models, this approach can be tested against microstructural data of creep loaded samples and thus provides higher reliability. Nevertheless, potential improvements are discussed and future developments are outlined.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 628-639, October 21–24, 2019,
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A new alloy design concept for creep- and corrosion-resistant, fully ferritic alloys was proposed for high-temperature structural applications in current/future fossil-fired power plants. The alloys, based on the Fe-30Cr-3Al (in weight percent) system with minor alloying additions of Nb, W, Si, Zr and/or Y, were designed for corrosion resistance though high Cr content, steam oxidation resistance through alumina-scale formation, and high-temperature creep performance through fine particle dispersion of Fe 2 (Nb,W)-type Laves phase in the BCC-Fe matrix. Theses alloys are targeted for use in harsh environments such as combustion and/or steam containing atmospheres at 700°C or greater. The alloys, consisting of Fe-30Cr-3Al-1Nb-6W with minor alloying additions, exhibited a successful combination of oxidation, corrosion, and creep resistances comparable or superior to those of commercially available heat resistant austenitic stainless steels. An optimized thermo-mechanical treatment combined with selected minor alloying additions resulted in a refined grain structure with high thermal stability even at 1200°C, which improved room-temperature ductility without sacrificing the creep performance. The mechanism of grain refinement in the alloy system is discussed.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 795-802, October 21–24, 2019,
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The cast microstructure of 1st generation MoSiBTiC alloy composed of Mo solid solution (Mo ss ), Mo 5 SiB 2 , TiC phases largely affects tensile-creep behavior in the ultrahigh temperature region. Mo 5 SiB 2 phase crystallized during solidification is plate-like with a size of several tens of microns. The plate surface is parallel to the (001) basal plane, and the <100] directions preferentially grow along the cooling direction, and thereby Mo 5 SiB 2 has a strong texture while Moss and TiC show randomly-oriented distribution in a cast ingot. During creep, Mo 5 SiB 2 plates are largely rotated and Moss works as sticky ligament in the small-plate-reinforced metal-matrix composites. This may be the reason why the MoSiBTiC alloy exhibits large creep elongation and excellent creep resistance. In other words, the evolution of microstructures infers that the consummation of Mo 5 SiB 2 plate rotation may lead to the initiation of creep rapture process. Therefore, the unique microstructure formed during solidification provides the feature of good mechanical properties for the 1st generation MoSiBTiC alloy.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 131-136, October 11–14, 2016,
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Nickel-based Alloy 617B (DIN 2.4673) and Alloy C-263 (DIN 2.4650) with high creep strength and good fabricability are promising material candidates for the design of next generation coal-fired “Advanced Ultra-Super-Critical A-USC” power plants with advanced steam properties and thus higher requirements on the material properties. Microstructural studies of the precipitation hardened alloy C-263 were performed with Electron Microscopy (TEM) with respect to their strengthening precipitates like carbides and intermetallic gamma prime. Specimens were subjected to different ageing treatments at elevated temperatures for different times. The microstructural results of the investigated nickel alloy C-263 are presented and discussed with respect to their correlation with required properties for A-USC, e.g. the mechanical properties, the creep resistance and the high temperature stability and compared to Alloy 617B. The manufacturing procedure for the prematernal and forgings as well as for thin walled tube components for A-USC power plants is presented.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 778-789, October 11–14, 2016,
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Sufficient energy availability in combination with lowest environmental pollution is a basic necessity for a high living standard in each country. To guarantee power supply for future generations, improved technologies to achieve higher efficiency combined with reduced environmental impact are needed. This challenge is not only aimed to the power station manufacturers, but also to the producers of special steel forgings, who have to handle with more and more advanced materials and complex processes. Bohler Special Steel is a premium supplier of forged high quality components for the power generation industry. This paper reports about experiences in the fabrication of forged components for steam turbines for ultra-supercritical application - from basic properties up to ultrasonic detectability results. The materials used so far are the highly creep-resistant martensitic 9-10% Cr steel class for operating temperatures up to 625°C developed in the frame of the European Cost research program. Additionally our research activities on the latest generation of high temperature resistant steels for operating temperatures up to 650 degree Celsius – the boron containing 9% Cr martensitic steels (MARBN) - are discussed. In order to improve the creep behavior, MARBN steels with different heat treatments and microstructures were investigated using optical microscopy, SEM and EBSD. Furthermore, short term creep rupture tests at 650 degree Celsius were performed, followed by systematic microstructural investigations. As a result it can be concluded, that advanced microstructures can increase the time to rupture of the selected MARBN steels by more than 10 percent.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 924-930, October 11–14, 2016,
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High efficiency in power generation is not only desirable because of economical reasons but also for enhanced environmental performance meaning reduced quantity of forming ash and emissions. In modern medium to large size plants, improvements require supercritical steam values. Furthermore, in future there will be an increasing share of renewables, such as wind and solar power, which will enhance the fluctuation of supply with the consequence that other power sources will have to compensate by operating in a more demanding cyclic or ramping mode. The next generation plant will need to operate at higher temperatures and pressure cycles coupled with demanding hot corrosion and oxidation environments. Such an operation will significantly influence the performance of materials used for boilers and heat exchanger components by accelerating oxidation rates and lowering mechanical properties like creep resistance. The paper discusses the oxidation behaviour of San25, 800H and alloy 263 in supercritical water at temperatures 650 and 700 °C at 250 bar, and compares the changes of mechanical properties of materials at these temperatures.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 1027-1035, October 11–14, 2016,
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In the present study a creep resistant, ferritic steel, based on the chemical composition of Crofer 22 H, was analysed regarding microstructure and particle evolution. Because of the preceding hot-rolling process formation of sub-grain structures was observed, which disappears over time. Additionally formation of particle-free zones close to high angle grain boundaries was observed. These zones are considered to be responsible for long-term material failure by lacking particle hardening and thus a concentration of deformation. Therefore in-depth analyses by transmission and scanning electron microscopy were performed to investigate dislocation behaviour in these areas
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 1058-1066, October 11–14, 2016,
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Higher steam temperature in steam power plants increases their thermal efficiency. Thus there is a strong demand for new materials with better creep and corrosion resistance at higher temperatures, while retaining the thermal flexibility of martensitic steels. Z-phase strengthened 12% Cr steels have been developed to meet the 923 K (650°C) challenge in these power plants. Ta, Nb, or V forms Z-phase together with Cr and N. A new trial steel was produced based on combining Ta and Nb to form Z-phase. It was shown that Z-phase was formed with a composition corresponding to Cr1+x(Nb,Ta)1-xN. The Nb/Ta ratio in Z-phase precipitates was higher than that in MX precipitates. Z-phase precipitates based on Ta and Nb were coarser than precipitates in a similar trial steel based on Ta alone.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 1067-1074, October 11–14, 2016,
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A 10%Cr martensitic steel with 3%Co and 0.008%B exhibits extremely long creep rupture time of approximately 40000 h under an applied stress of 120 MPa at a temperature of 650°C. The steel’s microstructure after creep tests interrupted at different creep stages was examined by transmission and scanning electron microscopy. It was shown that superior creep resistance of this steel was attributed to slow increase in creep rate at the first stage of tertiary creep whereas the rapid acceleration of creep rate took place only at the short second stage of tertiary creep. Transition from minimum creep rate stage to tertiary creep was found to be accompanied by coarsening of Laves phase particles, whereas M 23 C 6 – type carbides demonstrated high coarsening resistance under creep condition. Strain-induced formation of Z-phase does not affect the creep strength under applied stress of 120 MPa due to nanoscale size of Z-phase particles.
Proceedings Papers
AM-EPRI2013, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Seventh International Conference, 131-142, October 22–25, 2013,
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To achieve the necessary creep-rupture lifetimes at the temperatures and pressures associated with advanced ultrasupercritical (A-USC) steam conditions (100,000 h at 100 MPa and 760°C), precipitation-strengthened nickel-based alloys are required for the superheater and reheater tubing in A-USC boilers. Two alloys were considered to have potential for this application: Inconel 740 and Haynes 282 alloy. In support of this application, creep-rupture testing of several heats of Inconel 740 was conducted over a range of temperatures and stresses to develop confidence in qualitatively predicting creep lifetimes under conditions relevant to A-USC steam conditions, with the longest rupture times exceeding 30,000 h. For comparison, the creep-rupture behavior of Haynes 282 alloy was mapped as a function of temperature and stress, but with a significantly smaller dataset. Only a small difference in creep-rupture results between Inconel 740 and Inconel 740H was found although the latter alloy showed significantly greater resistance to η phase formation during testing. Little effect of prior aging treatments (for setting the γ′ precipitate structure) on creep-rupture behavior was observed. Results from a modified power law analysis showed that, while both Inconel 740 and Haynes 282 are projected to meet the A-USC lifetime requirements, the latter offered the potential for better long-term creep resistance.
Proceedings Papers
AM-EPRI2013, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Seventh International Conference, 992-1005, October 22–25, 2013,
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Dynamic development of steels used in power engineering industry for the production of boilers characterised by supercritical parameters poses new welding challenges. The introduction of new combinations of alloying agents aimed at obtaining the best possible mechanical properties, including creep resistance, affects the weldability of new steels. Each of the latter have to undergo many tests, particularly as regards bending and welding, in order to enable the development of technologies ensuring failure-free production and assembly of boiler systems. Martensitic steels containing 9% Cr, used in the manufacturing of steam superheaters, are characterised by good creep resistance and, at the same time, low oxidation resistance at a temperature in excess of 600°C. In turn, steels with a 12% Cr content are characterised by significantly higher oxidation resistance, but accompanied by lower strength at higher temperatures, which translates to their limited application in the production of boilers operating at the highest parameters. The niche between the aforesaid steels is perfectly filled by austenitic steels, the creep resistance and oxidation resistance of which are unquestionable. This article presents experience gained while welding dissimilar joints of advanced steels TEMPALOY AA-1 and T92, with the use of EPRI P87, Inconel 82 and Inconel 617 filler metals. The tests involving the said steel grades belong to the very few carried out in the world.
Proceedings Papers
AM-EPRI2013, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Seventh International Conference, 1352-1362, October 22–25, 2013,
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In this study, we have examined the creep of a novel austenitic heat resistant steel of Fe-20Cr- 30Ni-2Nb (at.%) steel at 1073K in steam and air atmospheres. Our studied steels were Fe-20Cr- 30Ni-2Nb (base steel) and that with 0.03 at. %B (B-doped steel) . The addition of boron is to intentionally increase the area fraction of Laves phase on grain boundaries (ρ). The specimen with ρ = 43% (base steel pre-aged at 1073 K/240 h) exhibits the rupture life of 262 h, whereas the rupture life of the specimen with higher ρ of 80% (B-doped steel pre-aged at 1073 K/240 h) is 833h, which is about three times longer than that of the specimen with ρ = 43%. The specimen with ρ = 80% exhibits smaller creep rate than those with lower ρ than 43% in the entire creep stage. In addition, all specimens show the creep rupture strain of about 60%. The creep rupture life is almost same to that tested under air, whereas the creep rupture strain is slightly smaller (a few percent) than that under air. In the surface of the creep ruptured specimen in steam, the intergranular oxides associated with voids or cavities are often present and grow along grain boundaries to over 100 μm in depth. The intergranular oxidation occurs more extensively in steam rather than air. These results demonstrate that stable Fe 2 Nb Laves phase on grain boundary could increase the creep resistance of the present steel at 1073K without ductility loss in steam as well as air, resulting in the pronounced extension of rupture life. The intergranular oxidation accelerated by steam would not give a serious effect on the creep properties of the present steel below 103 hours in rupture life.
Proceedings Papers
AM-EPRI2010, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Sixth International Conference, 127-139, August 31–September 3, 2010,
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ASTM Grade 23 is a 2.25Cr-0.3Mo-1.5W-V-Nb-B steel widely used for the fabrication of boiler components of the most recent ultra super critical power plants; it combines high creep resistance, enhanced oxidation and corrosion resistance and good weldability. Microstructural, mechanical, and creep properties of seamless tubes and pipes after normalizing and tempering heat treatment are compared with those obtained after cold bending and hot induction bending. The creep resistance is obtained through the precipitation of fine carbides after tempering. A broad program of TEM investigations on crept samples has been carried out in order to assess the evolution of the microstructure and its phases after long term high-temperature exposure, in terms of chemical composition, size and distribution of precipitates.
Proceedings Papers
AM-EPRI2010, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Sixth International Conference, 288-302, August 31–September 3, 2010,
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The Department of Energy and Ohio Coal Development Office jointly sponsored research to evaluate materials for advanced ultrasupercritical (A-USC) coal power plants, testing both monolithic tube materials and weld overlay combinations under real operating conditions. Testing was conducted in the highly corrosive, high-sulfur coal environment of Reliant Energy's Niles Plant Unit 1 boiler in Ohio. After 12 months of exposure, researchers evaluated six monolithic tube materials and twelve weld overlay/tube combinations for their high-temperature strength, creep resistance, and corrosion resistance in both steam-side and fire-side environments. Among the monolithic materials, Inconel 740 demonstrated superior corrosion resistance with the lowest wastage rate, while EN72 emerged as the most effective weld overlay material across various substrates, offering consistent protection against corrosion.
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