Haynes 282 alloy is a relatively new Ni-based superalloy that is being considered for advanced ultrasupercritical (A-USC) steam turbine casings for steam temperatures up to 760°C. Weld properties are important for the turbine casing application, so block ingots of Haynes 282 alloy were cast for properties studies. Good, sound welds were produced using Haynes 282 weld-wire and a hot gas-tungsten-arc welding method, and tensile and creep-rupture properties were measured on cross-weld specimens. In the fully heat-treated condition (solution annealed + aged), the tensile properties of the welded specimens compare well with as-cast material. In the fully heat-treated condition the creep-rupture life and ductility at 750°C/250MPa and 800°C/200MPa of the cross-weld specimens are similar to the as-cast base metal, and repeat creep tests show even longer rupture life for the welds. However, without heat-treatment or with only the precipitate age-hardening heat-treatment, the welds have only about half the rupture life and much lower creep ductility than the as-cast base metal. These good properties of weldments are positive results for advancing the use of cast Haynes 282 alloy for the A-USC steam turbine casing application.

A global movement is pushing for improved efficiency in power plants to reduce fossil fuel consumption and CO 2 emissions. While raising operating temperatures and pressures can enhance thermal efficiency, it necessitates materials with exceptional high-temperature performance. Currently, steels used in power plants operating up to 600°C achieve efficiencies of 38-40%. Advanced Ultra Supercritical (A-USC) designs aim for a significant leap, targeting steam temperatures of 700°C and pressures of 35 MPa with a lifespan exceeding 100,000 hours. Ni-based superalloys are leading candidates for these extreme conditions due to their superior strength and creep resistance. Haynes 282, a gamma prime (γ′) precipitation-strengthened alloy, is a promising candidate for A-USC turbine engines, exhibiting excellent creep properties and thermal stability. This research investigates the microstructural evolution in large, sand-cast components of Haynes 282. Microstructure, referring to the arrangement of grains and phases within the material, significantly impacts its properties. The research examines the alloy in its as-cast condition and after various pre-service heat treatments, aiming to fully identify and quantify the microstructural changes. These findings are then compared with predictions from thermodynamic equilibrium calculations using a dedicated Ni alloy database. The research reveals that variations in heat treatment conditions can significantly affect the microstructure development in Haynes 282, potentially impacting its mechanical properties.

The harsh operating conditions of Advanced Ultra-Supercritical (A-USC) power plants, i.e., steam operation conditions up to 760°C (1400°F)/35 MPa (5000 psi), require the use of Ni-based alloys with high temperature performance. Currently, the U.S. Department of Energy Fossil Energy program together with Electric Power Research Institute (EPRI) and Energy Industries of Ohio (EIO) is pursuing a Component Test (Comets) project to address material- and manufacturing-related issues for A-USC applications. Oak Ridge National Laboratory (ORNL) is supporting this project in the areas of mechanical and microstructure characterization, weld evaluation, environmental effect studies, etc. In this work, we present results from these activities on two promising Ni-based alloys and their weldments for A-USC applications, i.e., Haynes 282 and Inconel 740H. Detailed results include microhardness, tensile, air and environmental creep, low cycle fatigue, creep-fatigue, environmental high cycle fatigue, and supporting microstructural characterization.

Prior to utilizing new advanced materials in coal power plants, a large number of experimental testing is required. Test procedures are needed in specialized high temperature laboratories with state of the art facilities and precise, accurate analytical equipment capable of performing tests at a variety of temperatures and environments. In this study, the results of a unique technique involving salt spray testing at high temperatures are presented. The Haynes 282 gamma – prime (γ’) strengthened alloy fabricated by means of three different manufacturing processes: HAYNES 282 WROUGHT alloy, Haynes 282-SINT alloy, and finally Haynes 282-CAST alloy have been tested. The materials have been exposed to a salt spray corrosion atmosphere using 1% NaCl - 1% Na 2 SO 4 . Post exposure investigations have included SEM, EDS and XRD examinations. The test using salt spray of 1% NaCl - 1% Na 2 SO 4 water solution at 550 °C for 500 hours indicted no influence on the corrosion products formation, where Cr 2 O 3 has been developed in all three alloys, whereas NiO has been found only in Haynes 282-CAST material. On the other hand, it has been found that the fabrication process of HAYNES 282 alloy strongly influences the corrosion products formation under the high temperature exposures.

The United States Department of Energy Office of Fossil Energy and the Ohio Coal Development Office (OCDO) have led a U.S. consortium tasked with development of the materials technology necessary to build an advanced-ultra-Supercritical (A-USC) steam boiler and turbine with steam temperatures up to 760°C (1400°F). Part of this effort has focused on the need for higher temperature capable materials for steam turbine components, specifically cast nickel-base superalloys such as Haynes 282 alloy. As the size of the needed components is much larger than is capable of being produced by vacuum casting methods typically used for these alloys, an alternative casting process has been developed to produce the required component sizes in Haynes 282 alloy. The development effort has progressed from production of sub-scale sand castings to full size sand and centrifugal castings. The aim of this work was to characterize the microstructure and properties of a nickel alloy 282 casting with section size and casting weights consistent with a full sized component. A 2720 kg (6000 lbs.) nickel alloy 282 sand casting was produced and heat treated at MetalTek International. The casting was a half valve body configuration with a gating system simulated and optimized to be consistent with a full sized part. Following casting, heat treatment and NDE inspections, the half valve body was sectioned and tested. Tensile and high temperature creep was performed on material from different casting section thicknesses. Further analysis of the microstructure was carried out using light microscopy (LM), scanning electron microscopy (SEM), and X-ray spectroscopy (EDS). The paper also presents the mechanical properties obtained from the various sections of the large casting.

The Advanced Ultrasupercritical (A-USC) power plants are aimed to operate at steam inlet temperatures greater than 700°C; consequently, a complete materials overhaul is needed for the next-generation power plants. HAYNES 282, a gamma-prime strengthened alloy, is among the leading candidates because of its unique combination of properties, superior creep and LCF strength, fabricability and thermal stability. It is currently being evaluated in wrought and cast forms for A-USC turbine rotors, casings, boiler tubings, header, and valves. The candidate materials for A-USC applications not only require oxidation resistance for steam cycles but fireside corrosion resistance to coal ash is also of an extreme importance. In order to study the effect of both environments on the performance of 282 alloy, the alloy was exposed for extended periods in various oxidizing environments, such as air, air plus water vapor (10%), and 17bar steam up to 900°C. The fireside corrosion resistance of 282 alloy was evaluated at 700°C in synthetic coal ash and at 843°C in alkali salt deposits in a controlled gaseous environment.

Haynes 282 is a great candidate to meet advanced ultra-super-critical (A-USC) steam conditions in modern coal-fired power plants. The standard 2-step aging treatment has been designed for optimizing microstructure therefore providing excellent mechanical properties. We studied an alternative, more economical, 1-step aging treatment and compared microstructure, tensile properties at 750˚C and deformation behavior. Moreover, three cooling rates from the solution temperature were studied to simulate large-scale components conditions. We found that as much as about 20% of fine spherical intragranular γ' particles were successfully precipitated in all cases. Their average size increased as the cooling rate decreased. All four heat-treated alloys exhibited good mechanical properties at 750˚C with a yield strength well over 620MPa. As expected, the yield strength increased and the ductility decreased as the average γ' size decreased. The alloys exhibited a mixed mode of deformation, though the dominant deformation mechanism depended on the different γ' characteristics. The major operative deformation mechanism could be well predicted by strength increment calculations based on the precipitation strengthening model. Our results suggest that wrought Haynes 282 produced by a more economical 1-step aging treatment may be a reliable candidate for high temperature applications under A-USC conditions.

The United States Department of Energy (U.S. DOE) Office of Fossil Energy and the Ohio Coal Development Office (OCDO) have been the primary supporters of a U.S. effort to develop the materials technology necessary to build and operate an advanced-ultrasupercritical (A-USC) steam boiler and turbine with steam temperatures up to 760°C (1400°F). The program is made-up of two consortia representing the U.S. boiler and steam turbine manufacturers (Alstom, Babcock & Wilcox, Foster Wheeler, Riley Power, and GE Energy) and national laboratories (Oak Ridge National Laboratory and the National Energy Technology Laboratory) led by the Energy Industries of Ohio with the Electric Power Research Institute (EPRI) serving as the program technical lead. Over 10 years, the program has conducted extensive laboratory testing, shop fabrication studies, field corrosion tests, and design studies. Based on the successful development and deployment of materials as part of this program, the Coal Utilization Research Council (CURC) and EPRI roadmap has identified the need for further development of A-USC technology as the cornerstone of a host of fossil energy systems and CO 2 reduction strategies. This paper will present some of the key consortium successes and ongoing materials research in light of the next steps being developed to realize A-USC technology in the U.S. Key results include ASME Boiler and Pressure Vessel Code acceptance of Inconel 740/740H (CC2702), the operation of the world’s first 760°C (1400°F) steam corrosion test loop, and significant strides in turbine casting and forging activities. An example of how utilization of materials designed for 760°C (1400°F) can have advantages at 700°C (1300°F) will also be highlighted.

The Haynes 282 Ni-based superalloy (57Ni-20Cr-10Co-8.5Mo-2.1Ti-1.5Al) is a very promising candidate for the fabrication by additive manufacturing of gas turbine components of complex geometries. Alloy 282 was fabricated by electron beam melting (EBM) and exposed to two different heat treatments, (a) solution anneal (SA) at 1135°C followed by the standard 2-step aging treatment (2h at 1010°C plus 8h at 788°C) and (b) SA followed by 4h 800°C. Large elongated grains were observed for the as-fabricated and annealed EBM 282 materials, with a γ′ (Ni 3 (Al,Ti)) average size of ~100 nm and 20 nm, respectively. The as-fabricated EBM 282 alloy exhibited good ductility at 20-900°C and tensile strength slightly lower than the tensile strength of wrought 282. Annealing the alloy resulted in a moderate increase of the alloy strength at 800 and 900°C but a decrease of the alloy ductility. The creep lifetime at 800°C, 200MPa of the as-fabricated and annealed EBM 282 specimens machined along the build direction was 2 times and 1.5 times superior to the expected lifetime for wrought 282, respectively. For creep specimens machined perpendicular to the build direction, the lifetimes were ~25% lower compared to the wrought alloy. These creep results are directly related to the strong grain texture of the EBM 282 alloy and the limited impact of the initial γ′ (Ni 3 (Al,Ti)) size on alloy 282 creep properties.

Following the successful completion of a 15-year effort to develop and test materials that would allow advanced ultra-supercritical (A-USC) coal-fired power plants to be operated at steam temperatures up to 760°C, a United States-based consortium has been working on a project (AUSC ComTest) to help achieve technical readiness to allow the construction of a commercial scale A-USC demonstration power plant. Among the goals of the ComTest project are to validate that components made from the advanced alloys can be designed and fabricated to perform under A-USC conditions, to accelerate the development of a U.S.-based supply chain for key A-USC components, and to decrease the uncertainty for cost estimates of future commercial-scale A-USC power plants. This project is intended to bring A-USC technology to the commercial scale demonstration level of readiness by completing the manufacturing R&D of A-USC components by fabricating commercial scale nickel-based alloy components and sub-assemblies that would be needed in a coal fired power plant of approximately 800 megawatts (MWe) generation capacity operating at a steam temperature of 760°C (1400°F) and steam pressure of at least 238 bar (3500 psia).The A-USC ComTest project scope includes fabrication of full scale superheater / reheater components and subassemblies (including tubes and headers), furnace membrane walls, steam turbine forged rotor, steam turbine nozzle carrier casting, and high temperature steam transfer piping. Materials of construction include Inconel 740H and Haynes 282 alloys for the high temperature sections. The project team will also conduct testing and seek to obtain ASME Code Stamp approval for nickel-based alloy pressure relief valve designs that would be used in A-USC power plants up to approximately 800 MWe size. The U.S. consortium, principally funded by the U.S. Department of Energy and the Ohio Coal Development Office under a prime contract with the Energy Industries of Ohio, with co-funding from the power industry participants, General Electric, and the Electric Power Research Institute, has completed the detailed engineering phase of the A-USC ComTest project, and is currently engaged in the procurement and fabrication phase of the work. This paper will outline the motivation for the effort, summarize work completed to date, and detail future plans for the remainder of the A-USC ComTest project.

The drive for reduced carbon dioxide emissions and improved efficiency in coal fire power plant has led to much work being carried out around the world with regards to material development to enable 700+°C steam temperature operation. At these elevated temperatures and pressures steels just don’t have enough strength, and typically have a temperature limit of around 620°C (possibly up to 650°C in the near future) in the HP environment. Therefore, material development has focused on nickel alloys. European programs such as AD700, COMTES, European 50+ and more recently, NextGen Power and Macplus, have investigated the use of nickel alloys in the steam turbine. Large castings have an important role within the steam turbine, because valves bodies and turbine casings are nearly always produced from a cast component. The geometry of these components is often complex, and therefore, the advantage of using castings for such items is that near net shapes can be produced with minimal machining. This is important, as nickel alloys are expensive, and machining is difficult, so castings offer an attractive cost benefit. Cast shapes can be more efficiently designed with regards to stress management. For example, contouring of fillet regions can help to reduce stress concentrations leads to reduced plant maintenance and casting complex shapes reduces the number of onsite fabrication welds to inspect during outage regimes.

The US Advanced Ultra-Supercritical (A-USC) Consortium conducted an extensive program to evaluate available superalloys for use in rotors for steam turbines operating at a nominal temperature of 760 °C (1400 °F). Alloys such as 282, Waspaloy, 740H, 720Li, and 105 were tested in the form of bar supplied from the alloy producers. Ultimately, alloy 282 was down-selected for the turbine rotor based on its combination of creep strength, phase stability, ductility, and fatigue resistance. The next step in development was to produce a full-size rotor forging for testing. A team was established consisting of GE Power (project management and testing), Wyman-Gordon (forging and testing) and Special Metals (melting and billetizing) to pursue the work. A research license to melt the alloy was obtained from Haynes International. The first step of the development was to devise a triple melt (VIM-ESR-VAR) practice to produce 610 mm (24 inch) diameter ingot. Two ingots were made, the first to define the VAR remelting parameters and the second to make the test ingot utilizing optimum conditions. Careful attention was paid to ingot structure to ensure that no solidification segregation occurred. A unique homogenization practice for the alloy was developed by the US Department of Energy (DOE) and National Energy Technology Laboratory (NETL). Billetization was performed on an open die press with three upset and draw stages. This procedure produced an average grain size of ASTM 3. A closed die forging practice was developed based on compressive flow stress data developed by Wyman Gordon Houston for the consortium project. Multiple 18 kg forgings were produced to define the forging parameters that yielded the desired microstructure. The project culminated with a 2.19 metric ton (4830 lb), 1.22 m (48 inch) diameter crack-free pancake forging produced on Wyman Gordon’s 50,000 ton press in Grafton, MA. The forging process produced a disk with an average grain size of ASTM 8 or finer. Forging cut-up, microstructural characterization, and mechanical property testing was performed by GE Power. Fatigue and fracture toughness values of the disk forging exceeded those previously reported for commercially available rolled bar.

The necessity to reduce carbon dioxide emissions of new fossil plant, while increasing net efficiency has lead to the development of not only new steels for potential plant operation of 650°C, but also cast nickel alloys for potential plant operation of up to 700°C and maybe 750°C. This paper discusses the production of prototype MarBN steel castings for potential plant operation up to 650°C, and gamma prime strengthened nickel alloys for advanced super critical plant (A-USC) operation up to 750°C. MarBN steel is a modified 9% Cr steel with chemical concentration of Cobalt and tungsten higher than that of CB2 (GX-13CrMoCoVNbNB9) typically, 2% to 3 Co, 3%W, with controlled B and N additions. The paper will discuss the work undertaken on prototype MarBN steel castings produced in UK funded research projects, and summarise the results achieved. Additionally, within European projects a castable nickel based super alloy has successfully been developed. This innovative alloy is suitable for 700°C+ operation and offers a solution to many of the issues associated with casting precipitation hardened nickel alloys.

In both direct- and indirect-fired supercritical CO 2 (sCO 2 ) cycles, there is considerable interest in increasing the size and efficiency of such systems, perhaps by increasing the peak temperature to >700°C. However, relatively little experimental data are available under these conditions with pressures of 200-300 bar. Furthermore, impurities such as O 2 and H 2 O in the CO 2 may greatly alter the compatibility of structural alloys in these environments. While an experimental rig is being constructed that can measure and control the impurity levels in sCO 2 at 200-300 bar, initial 1 bar experiments at 700°-800°C for 500 h have been conducted in high-purity and industrial grade CO 2 , CO 2 +0.15O 2 and CO 2 +10%H 2 O and compared to exposures in dry air and 200 bar sCO 2 . These results, focusing on Fe- and Ni-base structural alloys and commercial chromia- and alumina-forming alloys, indicate that modifications in the environment did not strongly affect the reaction products at 700°-800°C.

The need to reduce carbon dioxide emissions of new fossil power plants is one of the biggest challenges of mankind in the next decades. In this context increasing net efficiency is the most important aspect which has led to the development of not only new steels for potential plant operation up to 650°C, but also to forged nickel alloys for 700°C and maybe 750°C. For steam temperatures of 700°C Alloy 617 and variants like TOS1x have been already intensively investigated, and manufacturability of large rotor parts was demonstrated. For operation temperatures of 750°C, only the use of γ‘ age-hardenable nickel base alloys is possible. Alloy 263 is one of the most promising alloys for manufacturing large forged components. For this material grade Saarschmiede has produced successfully a large rotor forging for the first time. Considering the complexity in manufacturing large nickel base alloy forgings, the implementation of simulation tools for calculation and optimization of production parameters becomes especially important. Numerical simulation methods are essential to predict material behavior and to optimize material quality-related manufacturing steps. In reference to mechanical properties, microstructure, uniformity of chemical composition FEM computer simulations for the key manufacturing processes re-melting, forging and heat treatment are in application. This paper will present the current status of production of very large prototype nickel base alloy rotor forgings for 700°C and 750°C A-USC power plants. Test results of an Alloy 617 large full scale turbine rotor component recently with improved properties produced will be highlighted. Experiences and results in applying numeric simulation models to ingot manufacturing and forging will also be reported.

Materials are the key to develop advanced ultra-supercritical (A-USC) steam generators. Operating at temperature up to 760°C and sustained pressure up to 4500 psi. Pressure vessel and piping materials may fail due to creep, oxidation, and erosion. Valves are particularly subjected to loss of function and leakage due to impermeant of the sealing surfaces. New materials, less susceptible to the above damage modes are needed for A-USC technology. Two Ni-based superalloys have been identified as prime candidates for valves based materials. Hardfacing is applied to sealing surfaces to protect them from wear and to reduce friction. Stellite 6 (Cobalt-based alloy) is the benchmark hardfacing owing to its anti-galling properties. However, the latest results tend to indicate that it is not suitable for high pressure application above 700°C. An alternative hardfacing will be required for A-USC. New Ni- and Co- based alloys are being developed for applications where extreme wear is combined with high temperatures and corrosive media. Their chemistry accounts for the excellent dry-running properties of these alloys and makes them very suitable for use in adhesive (metal-to- metal) wear. These new alloys have better wear, erosion, and corrosion resistance than Stellite 6 in the temperature range 800°C ~ 1000°C. As such, they have the potential to operate in A-USC. Velan recently developed an instrumented high temperature tribometer in collaboration with Polytechnique Montreal to characterize new alloys including static and dynamic coefficients of friction up to 800°C. We present herein the methodology that has been devolved to explore the effects of elevated temperature on the tribological behavior of those advanced material systems, with the goal of capturing the basis for the specification, design, fabrication, operation, and maintenance of valves for A-USC steam power plants.

A new nickel-base superalloy GH750 has been developed as boiler tube of advanced ultrasupercritical (A-USC) power plants at temperatures about and above 750°C in China. This paper researched the weld solidification of GH750 filler metal, microstructure development and property of GH750 welded joint by gas tungsten arc weld. Liquid fraction and liquid composition variation under non-equilibrium state were calculated by thermo-dynamic calculation. The weld microstructure and the composition in the dendrite core and interdendritic region were analyzed by SEM(EDX) in detail. The investigated results show that there is an obvious segregation of precipitation-strengthening elements during the weld solidification. Titanium and Niobium are the major segregation elements and segregates in the interdendritic region. It was found that the changing tendency of the elements’ segregation distribution during the solidification of GH750 deposit metal is agree with the thermodynamic calculation results. Till to 3,000hrs’ long exposure at 750°C and 800°C, in comparison with the region of dendrite core of solidification microstructure, not only the coarsening and the accumulation of γʹ particles are remarkable in the interdendritic region, but also the small quantity of the blocky and needle like η phases from. The preliminary experimental results indicate that the weakening effect of creep-rupture property of the welded joint is not serious compared with GH750 itself.

Inconel 740H is one of the most promising candidate Ni-base superalloys for the main steam pipe of 700 °C advanced ultra-supercritical (A-USC) coal-fired power plants. After processing and welding in manufacturing plant in solution-annealed state, large components was commonly suggested to have an extra aging treatment at 800 °C for 16 h, in order to obtain homogeneous γ′ precipitates. In this present work, creep tests and microstructure analyses were conducted on Inconel 740H pipe specimens under two different heat treatments to verify the necessity of aging process. Here we show that aging treatment has limited effect on the creep rupture life of Inconel 740H pipe. Both in grain interiors and along grain boundaries, crept specimens under two different heat treatments have the same precipitates. But the shape and distribution of γ′ in solution annealed sample is not as regular as the aged ones. Our results provide the underlying insight that aging treatment is not so necessary for the straight pipes if the on-site condition was hard to control. But for both groups of specimens, a small amount of h particles and some banded like M 23 C 6 were emerged during creep, which would be harmful to mechanical properties for the long run.