Advanced martensitic 9% chromium steels have been identified as the most favored group of materials for high temperature applications in thermal power plants. To extend the temperature range of martensitic steels up to 650°C large effort was put on the development of new alloy concepts. The so-called MARBN concept (Martensitic steel with defined Boron/Nitrogen relation) provides increased creep rupture strength due to higher solid solution strengthening and improved microstructural stability. The major improvement is the reduction of type IV cracking in welded joints, which shifts the focus to the creep rupture strength of the weld metal. This paper illustrates the process experience of the steel foundry for production of heavy cast components in latest state of the art 9-12%Cr-MoCoVNbNB-alloyed cast steel grades and the newest state of development and prototype components in MARBN cast steel grades. Metallurgy, solidification, heat treatment and welding are main items to be considered for development of new, complex steel grades for foundry processing with the help of empiric processing in test programs and thermo-physical simulation. As welding is an essential processing step in the production of heavy steel cast components a good out-of-position weldability is required. Moreover a stress-relieve heat-treatment takes place subsequently after welding for several hours. This contribution also deals with the development of matching welding consumables for the production of heavy cast components and discusses the challenges of defining appropriate welding and heat treatment parameters to meet the requirements of sufficient strength and toughness at ambient temperature. Additionally, first results of creep rupture tests are presented.

The voestalpine foundry group, operating at locations in Linz and Traisen, Austria, specializes in heavy steel casting components ranging from 1 to 200 tons for power generation, oil and gas, chemical processing, and offshore applications. Their manufacturing expertise encompasses high-alloyed martensitic 9-12% Cr-steels and nickel-based Alloy 625, particularly for ultra-supercritical (USC) and advanced USC power generation systems operating at temperatures from 600°C to over 700°C. The production of these complex, thick-walled components relies on advanced thermodynamic calculation and simulation for all thermal processes, from material development through final casting. The foundries’ comprehensive capabilities include specialized melting, molding, heat treatment, non-destructive testing, and fabrication welding, with particular emphasis on joining dissimilar cast, forged, and rolled materials. Looking toward future innovations, the group is exploring additive manufacturing for mold production and robotic welding systems to enhance shaping and surface finishing capabilities.

Steel castings of creep-resistant steels are critical components in the high and intermediate pressure turbine sections of fossil fuel-fired power plants. As plant efficiencies improve and emission standards tighten, steam parameters become more stringent, necessitating constant enhancement of material creep resistance. Steel foundries alone cannot conduct necessary material development at an appropriate scale, so all power plant component suppliers cooperate to define optimal chemical compositions, perform test melts, creep tests, microstructure investigations, and test pilot components, such as through the COST program developing new 9-12%Cr cast steel grades. This paper illustrates a steel foundry's role in COST, describing the transfer of these new cast steel grades from research into commercial production of heavy cast components, outlining incurred problems, process development cycles, comparisons with low-alloy steels, welding tests, base material/weld investigations, heat treatment optimization, and casting of pilot components/weldability test plates to verify castability of larger parts and make necessary adjustments. Parallel to ongoing COST creep tests, the steel grades were introduced into commercial large component production, involving solutions to process-related issues, with over 180 components successfully manufactured to date, while further COST program developments present ongoing challenges.

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 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.

We have reported on the effort being done to develop the A-USC technology in Japan, which features the 700 deg-C steam condition, since the 2007 EPRI conference. Our 9 year project began in 2008. There have been some major changes in the electricity power market in the world recently. At first, the earthquake changed the power system violently in Japan. Almost all nuclear power plants have been shut down and natural gas, oil and coal power plants are working fully to satisfy the market's demands. In the USA, the so called ‘Shale gas revolution’ is going on. In Europe, they are working toward the target of reducing CO 2 emissions by the significant use of renewables with the backup of the fossil fuel power systems and enhancing power grids. A very rapid increase in power generation by coal is being observed in some countries. Despite some major changes in the electric sector in the world and the CO 2 problem, the global need for coal power generation is still high. We can reconfirm that the improvement of the thermal efficiency of coal power plants should be the most fundamental and important measure for the issues we are confronting today, and that continuous effort should be put towards it. Based on the study we showed at the 2007 conference, we developed 700 deg-C class technology mainly focusing on the material and manufacturing technology development and verification tests for key components such as boilers, turbines and valves. Fundamental technology developments have been done during the first half of the project term. Long term material tests such as creep rupture of base materials and welds will be conducted for 100,000hrs continuing after the end of the project with the joint effort of each participating company. Today, we are preparing the plan for the second half of the project, which is made up of boiler components test and the turbine rotating tests. Some boiler superheater panels, large diameter pipes and valves will be tested in a commercially operating boiler from 2015 to 2017. The turbine rotor materials which have the same diameter as commercial rotors will be tested at 700 deg-C and at actual speed.

To meet worldwide emission targets many Government policies either avoid the use of coal burning plant for future energy production, or restrict emissions per kilogram of coal consumed beyond the capability of most conventional plant. As a result this has accelerated current worldwide developments of steel and nickel alloys for coal-fired plant to operate at temperatures in excess of 625°C. Within the UK a modified 9%Cr steel has been developed which is based on the MarBN steel first proposed by Professor Fujio Abe of NIMS Japan, and has been designated IBN-1. The steel is modified by additions of, typically, 3% cobalt and tungsten with controlled additions of boron and nitrogen. While development of 9%Cr steels has continued since the last EPRI high temperature material conference in 2016 (Portugal), parallel developments in nickel alloy castings for even higher temperature and pressure applications have also continued. This paper summarises the latest developments in both of these material types.

The “Cool Earth-Innovative Energy Technology Program,” launched by the Japanese government in March 2008, aims to significantly reduce global greenhouse gas emissions. Among the 21 selected technologies is the Advanced Ultra Super Critical (A-USC) pressure power generation, which targets the commercialization of a 700°C class pulverized coal power system with a power generation efficiency of 46% by around 2015. As of 2004, Japan's pulverized coal power plant capacity reached 35 GW, with the latest plants achieving a steam temperature of 600°C and a net thermal efficiency of approximately 42% (HHV). Older plants from the 1970s and early 1980s, with steam temperatures of 538°C or 566°C, are nearing the need for refurbishment or rebuilding. A case study on retrofitting these older plants with A-USC technology, which uses a 700°C class steam temperature, demonstrated that this technology is suitable for such upgrades and can reduce CO 2 emissions by about 15%. Following this study, a large-scale development of A-USC technology began in August 2008, focusing on developing 700°C class boiler, turbine, and valve technologies, including high-temperature material technology. Candidate materials for boilers and turbine rotor and casing materials are being developed and tested. Two years into the project, useful test results regarding these candidate materials have been obtained, contributing to the advancement of A-USC technology.

Advanced Ultra-supercritical (A-USC) steam power-plant technology is being developed for better efficiency and lower emissions at 700°C and above, but is based mainly on Ni-based alloys. The ability to include lower-cost alloys with appropriate high-temperature performance should have substantial technological and economic benefits. CF8C-Plus is a cast austenitic stainless steel recently developed for other applications at 600-900°C, which has creep-strength comparable to many solid-solution Ni-based alloys. EPRI and Carpenter Technology produced a 400 lb heat of CF8C-Plus steel and hot-forged it at 5:1 and 12:1 reductions, to assess feasibility of the alloy as a wrought advanced stainless steel for potential use as steam headers and piping for A-USC power plant applications. The hot-forged alloy has a recrystallized grain structure 6-9 times finer than the as-cast dendritic structure, resulting in better strength and impact resistance at room-temperature, and about 20% higher yield-strength (YS) at 760°C, and similar or better ductility compared to the as-cast material. The initial creep-rupture testing at 700-800°C for up to 2000h also indicates similar or better rupture resistance and better creep-ductility for wrought compared to cast material. The next steps needed to test performance of the wrought austenitic stainless steel for extruded headers and piping are discussed.

Ultrasupercritical (USC) steam boiler and heat recovery steam generator (HRSG) technology is constantly evolving to improve efficiency and reduce emissions. Currently, temperatures are pushing beyond the capabilities of even the most advanced ferritic steels with some applications requiring nickel-based superalloys. Cost-effective design of these systems requires the application of a variety of alloys representing a range of cost/property trade-offs. CF8C-Plus is a cast austenitic stainless steel recently developed for application in high temperatures similar to those in power plants (600 - 900 °C) with creep strength comparable to several superalloys. This makes it an attractive alternative for those expensive alloys. EPRI, with assistance from PCC subsidiaries Special Metals and Wyman Gordon Pipes and Fittings, has produced and characterized two pipe extrusions nominally 5.25 inch OD x 0.5 inch wall thickness and 6 inch OD x 0.75 inch wall (13.3 x 1.3 cm and 15.2 x 1.9 cm), each about 1000 lbs, to continue to assess the feasibility of using a wrought version of the alloy in power piping and tubing applications. The mechanical properties from these extrusions show performance in the same population as earlier forging trials demonstrating capability exceeding several austenitic stainless steels common to the industry. Creep-rupture performance in these extrusions continues to be competitive with nickel-based superalloys.

Additive manufacturing is a groundbreaking manufacturing method that enables nearly lossless processing of high-value materials and produces complex components with a level of flexibility that traditional methods cannot achieve. Wire arc additive manufacturing (WAAM), utilizing a conventional welding process such as gas metal arc welding, is one of the most efficient additive manufacturing technologies. The WAAM process is fully automated and guided by CAD/CAM systems on robotic or CNC welding platforms. This paper explores the fundamental concepts and metallurgical characteristics of WAAM. It focuses primarily on the mechanical properties of printed sample structures made from P91, X20, and alloys 625 and 718 wire feedstock. The study particularly addresses the anisotropy of mechanical properties through both short-term and long-term testing, comparing these results to materials processed using conventional methods.

Enhancement of the steam conditions is one of the most effective measures to achieve the goal of higher thermal efficiency. 700°C class A-USC (Advanced Ultra Super Critical Steam Conditions) power plant is one of the remarkable technologies to achieve the goal and reduce CO 2 emissions from fossil fuel power plants. Toshiba has been working on the A-USC development project with subsidy from METI (Ministry of Economy, Trade and Industry) and NEDO (New Energy and Industrial Technology Development Organization). In this project, A-USC power plants with steam parameters of 35MPa 700/720/720°C were considered. To date, various materials have been developed and tested to verify their characteristics for use in A-USC power plants. And some of these materials are being investigated as to their suitability for use in long term. Together with members of the project, we carried out the boiler component test using a commercially-operating boiler. We manufactured a small-scale turbine casing made of nickel-based alloy, and supplied it for the test. In addition, we manufactured a turbine rotor for turbine rotation tests, and carried out the test at 700°C and rotating speed of 3,600rpm conditions. In this paper, we show the results of the A-USC steam turbine development obtained by the project.

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.

This paper presents an overview of China’s electric power development and the National 700°C Ultra-Supercritical (USC) Coal-Fired Power Generation Technology Innovation Consortium. Besides, the R&D plan and latest progress of China 700°C USC coal-fired power generation technology is also introduced in this paper.

CO 2 emission reduction from coal power plants is still a serious issue to mitigate the impact of global warming and resulting climate change, though renewables are growing today. As one of the solutions, we developed A-USC (Advanced Ultra Super Critical steam condition) technology to raise the thermal efficiency of coal power plants by using high steam temperatures of up to 700℃ between 2008 and 2017 with the support of METI (Ministry of Economy, Trade and Industry) and NEDO (New Energy and Industrial Technology Development Organization). The temperature is 100℃ higher than that of the current USC technology. Materials and manufacturing technology for boilers, turbines and valves were developed. Boiler components, such as super heaters, a thick wall pipe, valves, and a turbine casing were successfully tested in a 700℃-boiler component test facility. Turbine rotors were tested successfully, as well, in a turbine rotating test facility under 700℃ and at actual speed. The tested components were removed from the facilities and inspected. In 2017, following the component tests, we started a new project to develop the maintenance technology of the A-USC power plants with the support of NEDO. A pressurized thick wall pipe is being tested in a 700℃ furnace to check the material degradation of an actual sized component.

Austenitic and super-austenitic stainless steels are a critical component of the spectrum of high temperature materials. With respect to power generation, alloys such as Super 304H and NF709 span a gap of capability between ferritic and martensitic high chromium steels and nickel-based alloys in boiler tube applications for both conventionally fired boilers and heat-recovery steam generators (HRSG). This research explores a wrought version of a cast austenitic stainless steel, CF8C-Plus or HG10MNN, which offers promise in creep strength at relatively low cost. Various manufacturing techniques have been employed to explore the impact of wrought processing on nano-scale microstructure and ultimately performance, especially in high temperature creep. Transmission electron microscopy has been used to quantify and characterize the creep-strengthening particles examining the relationship between traditional melting and extrusion as compared to powder metallurgy.

Recent evidence suggests that using hardness as the sole acceptance criterion for Grade 91 steels is inadequate for predicting service performance. Components can achieve acceptable initial hardness values through heat treatment despite suboptimal elemental composition, leading to poor tempering resistance and unexpectedly low creep strength during service. Paradoxically, some components with lower initial hardness may perform better due to slower degradation rates. While the relationship between parent material properties and Type IV cracking susceptibility remains under investigation, heat-affected zones (HAZ) in welds are emerging as primary locations for service failures. This complexity emphasizes the need for comprehensive evaluation criteria incorporating stress, temperature, and material properties when assessing component serviceability.

Advanced UltraSupercritical (A-USC) Steam fossil power plants will operate at steam temperatures up to 760°C, which will require the use of Ni-based superalloys for steam boiler/superheater and turbine systems. In 2008, the Oak Ridge National Laboratory (ORNL) and the National Engineering Technology Laboratory/Albany (NETL/Albany) collaborated to make and test castings of Ni-based superalloys, which were previously only commercially available in wrought form. These cast Ni-based based alloys are envisioned for the steam turbine casing, but they may also be applicable to other large components that connect the steam supply to the steam turbine. ORNL and NETL/Albany have produced small vacuum castings of HR 282, Nimonic 105, Inconel 740, and alloy 263, which are precipitation-hardened Ni-based superalloys, as well as solid-solution superalloys such as alloys 625, 617 and 230. The initial alloy screening included tensile and creep-testing at 800°C to determine which alloys are best suited for the steam turbine casing application at 760°C. HR 282 has the best combination of high-temperature strength and ductility, making it a good candidate for the cast-casing application. Cast and wrought versions of HR 282 have similar creep-rupture strength, based on the limited data available to-date. Detailed comparisons to the other alloys and microstructures are included in this paper.

Additive manufacturing is being considered for pressure boundary applications for power plant service by ASME Boiler and Pressure Vessel Code and regulators. Both existing and new plants could benefit from the reduced lead times, design flexibility, and part consolidation possible with additive manufacturing. Various ASME code committees are working towards rules and guidance for use of additive manufacturing. To further the industry's understanding, this research program was undertaken to evaluate the properties of wire arc additive manufactured 316L stainless steel. This study included microstructural characterization, chemical composition testing, mechanical testing, and nondestructive evaluation of multiple large (1600-pound (700 kg)) 316LSi stainless steel valve bodies produced using the gas metal arc directed energy deposition process followed by solution annealing. The results showed the tensile behavior over a range of temperatures was comparable to wrought material. No variation in tensile behavior was observed with change in tensile sample orientation relative to the build direction. Room temperature Charpy V-notch absorbed energy toughness was comparable to wrought material. Large grain sizes were observed in the metallographic samples, indicating that lowering the solution anneal temperature may be worthwhile. The results of surface and volumetric examination were acceptable when compared to forged material acceptance criteria. Together these results suggest that GMA-DED can produce acceptable materials properties comparable to forged materials requirements.

Modified 9Cr-1Mo steel (ASTM Gr.91) is widely used in components of fossil fueled power plants around the world today. This grade of steel has however been shown to exhibit significant variations in creep life and creep ductility, which has led to premature in-service failures. The aim of this work is to define potential metallurgical risk factors that lead to this variation in performance. To achieve this, a set of creep test samples that represent a wide range in this variation of creep behavior in this steel grade have been studied in detail. As a first stage in this characterization the macro-scale chemical homogeneity of the materials were mapped using micro-XRF. Understanding the segregation behavior also allows quantification of microstructural parameters in both segregated and non-segregated areas enabling the variations to be determined. For example this showed a significant increase in the number per unit area of Laves phase particles in high compared with low Mo content areas. To study the effect of MX particles on segregation a methodology combining SEM and TEM was employed. This involved chemically mapping the larger V containing particles using EDS in the SEM in segregated and unsegregated areas and then comparing the results to site-specific TEM analysis. This analysis showed that although the average size of the V containing samples is in the expected 0-50 nm size range, these particles in some samples had a wide size distribution range, which significantly overlaps with the M 23 C 6 size distribution range. This together with the segregation characteristics has important implications for determining meaningful quantitative microstructural data from these microstructurally complex materials.