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.

COST FB2 steel alloyed with boron is currently the best available martensitic 9% Cr steel for turbine shafts subjected to steam temperatures up to 620°C and meanwhile introduced into production for application in commercial power plants. Currently several development programs are running to develop materials for further increase of application temperature up to 650°C. For realization of a 650ºC power plant not only creep strength, but also resistance against steam oxidation must be improved by increase of Cr content up to 11-12%. In the past all attempts to develop stable creep resistant martensitic 11-12% Cr steels for 650°C failed due to breakdown in long-term creep strength. Therefore new alloy concepts have been developed by replacing the fine nitride strengthening particles by controlled and accelerated precipitation of the more stable Z phase. Therefore the European project “Z-Ultra” was launched for further development and manufacture of this new alloy type. Saarschmiede participates in this project and contributed by manufacturing trial melts, boiler tubes and a large scale turbine rotor forging. Production experience and test results are presented. In order to exceed the temperature limit of 650°C, only nickel base alloys can be used. One of the most promising candidate alloys for rotor forgings subjected to steam temperatures of 700°C is Alloy 617, which was already intensively investigated. For still higher temperatures in the range of 750°C only γ‘-precipitation hardened nickel base alloys, such as Alloy 263, can be applied. Therefore the “NextGenPower” project was launched and aimed at manufacture and demonstration of parts from Ni-based alloys for application in steam power plants at 750°C. One of the main goals was to develop turbine rotor materials and to demonstrate manufacturability of forgings for full scale turbine rotor parts. Contributing to this project, Saarschmiede has produced for the first time a large rotor forging in the Ni base Alloy 263. Numeric simulations of ingot manufacture, forging and heat treatment have been performed and a large trial rotor forging in Alloy 263 with a diameter of 1000 mm was successfully produced from a triple melt ingot. Experiences in manufacture and test results are presented.

For safe operation of thick-walled components for Advanced Ultra Super Critical (A-USC) power plants, detailed knowledge of the creep crack initiation and growth behavior is essential. The high loading and high temperature conditions in an A-USC power plant require, in many cases, the employment of nickel base super alloys. Unfortunately, both manufacturing and nondestructive evaluation (NDE) of thick-walled components (> 50 mm) made of nickel base super alloys are quite challenging. In this paper, one candidate material for such applications, Alloy C-263, was tested for creep and creep crack behavior at 700 °C. Objective of the study was to determine a critical flaw size. In order to establish this size, the duration to achieve the 1%-strain limit at a given load is compared with the time to grow the initial flaw for Δa = 0.5 mm when the component was loaded with the same given load. It will be shown that manufacturing parameters, e. g. heat treatment procedures, have a significant influence on the creep crack initiation and growth behavior and thus on component life. Decoration of grain boundaries with precipitates, for instance caused by the manufacturing process, can reduce the creep crack resistance and thus increase the risk for premature component failure.

Austenitic heat resistant steels are one of the most promising materials to be applied around 650°C, due to its superior creep strength than conventional ferritic steels and lower material cost than Ni based superalloys. The problem of austenitic steels is its high thermal expansion coefficient (CTE), which leads to high deformation and stress when applied in rotors, casings, blades and bolts. To develop low CTE austenitic steels together with high temperature strength, we chose the gamma-prime strengthened austenitic steel, A-286, as the base composition, and decreased the CTE by introducing the invar effect. The developed alloy, Fe-40Ni-6Cr-Mo-V-Ti-Al-C-B, showed low CTE comparable to conventional ferritic steels. This is mainly due to its high Ni and low Cr composition, which the invar effect is prone even at high temperature region. This alloy showed higher yield strength, higher creep rupture strength and better oxidation resistance than conventional high Cr ferritic steels and austenitic steels. The 2 ton ESR ingot was forged or hot rolled without defects, and the blade trial manufacturing was successfully done. This alloy is one of the best candidates for USC and A-USC turbine components.

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.

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.

Microstructure in the gage sections of ruptured GX12CrMoWVNbN10-1-1 cast steel specimens was examined after creep tests under applied stresses ranging from 120 to 160 MPa at T=893 K. The microstructure after tempering consisted of laths with an average thickness of 332 nm. The tempered martensite lath structure was characterized by M 23 C 6 -type carbide particles with an average size of about 105 nm, and MX carbonitrides with an average size of about 45 nm. Precipitation of Laves phase occurred during creep test. The structural changes in the gauge section of the samples were characterized by the evolution of relatively large subgrains with remarkably lowered density of interior dislocations within former martensite laths. MX carbonitrides and M 23 C 6 -type carbide particles increase in size slightly under long-term creep. Microstructural degradation mechanisms during creep in GX12CrMoWVNbN10-1-1 cast steel are discussed.

Work has been progressing over recent years to develop a standard test method for high temperature solid particle erosion testing. Early in 2015 this standard was published by ASTM as G211-14 Standard Test Method for Conducting Elevated Temperature Erosion Tests by Solid Particle Impingement Using Gas Jets. To support the development of this standard the European funded METROSION project has been conducting a comparison of different apparatus which employ different nozzle geometries, acceleration lengths, stand-off distances and heating and accelerating processes. The aim is to understand the influence these instrumental and experimental parameters have on the measured erosion rate and erosion mechanism. As part of this work three very distinct approaches have been compared using a common erodent and test pieces. Measurements have been performed at 600 °C with particle velocities of 50 to 320 m/s, using different stand-off distances, acceleration lengths and nozzle diameters for impact angles of 30 and 90°. This is the first time a comprehensive comparison of these parameters has been conducted and shows the relative influence of these experimental variables.

Additive manufacturing (AM) is a process where, as the name suggests, material is added during production, in contrast to techniques such as machining, where material is removed. With metals, AM processes involve localised melting of a powder or wire in specific locations to produce a part, layer by layer. AM techniques have recently been applied to the repair of gas turbine blades. These components are often produced from nickel-based superalloys, a group of materials which possess excellent mechanical properties at high temperatures. However, although the microstructural and mechanical property evolution during the high temperature exposure of conventionally produced superalloy materials is reasonably well understood, the effects of prolonged high temperature exposure on AM material are less well known. This research is concerned with the microstructures of components produced using AM techniques and an examination of the effect of subsequent high temperature exposures. In particular, the paper will focus on the differences between cast and SLM IN939 as a function of heat treatment and subsequent ageing, including differences in grain structure and precipitate size, distribution and morphology, quantified using advanced electron microscopy techniques.

A failure of the upper casing of the circulation pump led to a big damage in the PP Staudinger unit 5 on 12th of May 2014. According to the §18(2) BetrSichV an extensive root cause analysis (RCA) was started. From the beginning on different lines of activities were initiated to handle the situation with the required diligence. Decisions were made, taking into account safety regulations, possibility of repair and best practice engineering. Following the board decision to repair the unit 5, a lot of detailed work was done. All of the performed work packages were linked in different timelines and needed to meet in the key points. Consequently it was a challenge to achieve the agreed date of unit 5 restart on 15th of January 2015. The unit restart on the targeted date was a proof of the excellent collaboration between all involved parties. The presentation gives a summarizing overview about the damage, the main results of the RCA and the repair activities.

In previous investigations on life with flexible driving were highly stressed components predominantly in hot continuous pressurized part of power plants in the foreground. However cases of damage and subsequent studies on peripheral components such as the boiler circulation system (boiler circulating pump) showed that a potential failure as well as a high hazard potential respectively great consequential damage can occur when such components are operated under different conditions. To avoid damages and losses resulting from damage to peripheral components, these components have to be subjected to further analysis. Here especially the pump housing is in the focus.

Due to a high degree of mixing between substrate and weld deposit, fusion welding of dissimilar metal joints functionally produce new, uncharacterized alloys. In the power generation industry, such mixing during the application of cobalt-based hardfacing has led to a disconcerting number of failures characterized by the hard overlay welds disbonding. Investigations into this failure mechanism point to the unknown alloy beneath the surface of the hardfacing layer transforming, hardening, and becoming brittle during service. This research describes a methodology for exploring a chemical space to identify alloy combinations that are expected to be safe from deleterious phase formation. Using thermodynamic modeling software and a stepped approach to potential chemistries, the entire phase stability space over the full extent of possible mixing between substrate and weld material can be studied. In this way diffusion effects – long term stability – can also be accounted for even in the case where mixing during application is controlled to a low level. Validation of predictions specific to the hardfacing system in the form of aged weld coupons is also included in this paper. Though the application of this methodology to the hardfacing problem is the focus of this paper, the method could be used in other weld- or diffusion- combinations that are expected to operate in a high temperature regime.

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.

In this study, a possibility of application of advanced 9%Cr steel containing 130 ppm boron for boiler components utilized at around 650 °C to higher temperature steam turbine rotor materials has been investigated by means of reduction in silicon promoting macro-segregation in the case of large size ingots, using laboratory heats. Tempered martensitic microstructure without proeutectoid ferrite in all steels studied is obtained even at the center position of a turbine rotor having a barrel diameter of 1.2 m despite lower amounts of nitrogen and silicon. The strength at room temperature is almost the same level of practical high Cr steels such as X13CrMoCoVNbNB 9-2-1 for ultrasuper critical steam turbine rotors. The toughness is sufficient for high temperature rotors in comparison with CrMoV steels utilized as sub-critical high pressure steam turbine components. The creep rupture strength of the steels is higher than that of the conventional 9-12Cr steels used at about 630 °C. The creep rupture strength of 9%Cr steel containing 130 ppm B, 95 ppm N, 0.07 % Si and 0.05 % Mn is the highest in the steels examined, and it is therefore a candidate steel for high temperature turbine rotors utilized at more than 630 °C. Co-precipitation of M 23 C 6 carbides and Laves phase is observed around the prior austenite grain boundaries after the heat treatments and the restraint of the carbide growth is also observed during creep exposure. An improvement in creep strength of the steels is presumed to have the relevance to the stabilization of the martensitic lath microstructure in the vicinity of those boundaries by such precipitates.

Based on the research and development of Ni-based alloy of 700°C steam turbine bolts and blades worldwide, the process, microstructure, properties characteristics and strengthening mechanism of typical 700°C steam turbine bolts and blades materials Waspaloy are discussed in this study. The result shows that Waspaloy has higher elevated temperature yield strength, creep rupture strength, anti-stress relaxation property and good microstructure stability. The Waspaloy alloy could meet the design requirements of 700°C steam turbine bolts and blades.

Sufficient available energy in combination with lowest environmental pollution is a basic necessity for a high standard of living in every country. In order to guarantee power supply for future generations it is necessary to use fossil fuels as efficient as possible. This fact calls for the need of power plants with improved technologies to achieve higher efficiency combined with reduced environmental impact. In order to realize this goal it is not only a challenge for power station manufacturers, but also for manufacturers of special steels and forgings, who have to produce improved components with more advanced materials and more complex manufacturing processes. This paper reports about experiences in the fabrication of forged components for gas and steam turbines followed by achievable mechanical properties and ultrasonic detectability results. The materials are the creep resistant martensitic Cr steels developed in the frame of the European Cost research programme. Whereas Boron containing 10% Cr steels are suitable for steam temperatures of 625°C and slightly higher, Ni-based alloys shall be used for temperatures of 700°C and above. One pilot rotor forging, representing a HP-rotor for welded construction, has been manufactured out of alloy Inconel 625 within the frame of the European Thermie project AD700.

Microstructural change of 10 % Cr steel trial forgings subjected to different heat treatment conditions which aim to improve the creep rupture strength and microstructural stability during creep was investigated. Creep rupture strength of the forging subjected to the quality heat treatment with the austenitizing temperature of 1090° C is higher than that of the forging solution treated at 1050°C, however, the difference of creep rupture strength is reduced in the long-term region around 40,000 h. Decrease in creep rupture ductility of the forging until 43,300 h is not observed. Progress of the martensite lath recovery in the forging solution-treated at 1090°C is slower than that in the forging austenitized at 1050°C. Higher temperature solution treatment suppresses the recovery of lath structures. Formations of Z-phase are found in the specimens creep-ruptured at 37,300 h in the forging solution-treated at 1050°C and at 43,400 h in the forging austenitized at 1090°C. Z-phase precipitation behavior in this steel is delayed in comparison with the boiler materials, regardless of austenitizing temperature.

Driven by the need to reduce CO 2 emissions through increased steam temperature and pressure in new power plants, research in Europe led to the development of enhanced high-chromium steels with improved creep resistance and service temperature stability. After years of development, Rotor E, a steel composition created during the COST programs (501, 522, and 536), has become a commercially available product. While traditionally forged and remelted using electroslag remelting (ESR), this paper demonstrates the successful production of large rotor components using a conventional process without ESR, achieved through tailored process control. This paper details Società delle Fucine's (SdF) current production of Rotor E using a conventional route based on ladle furnace and vacuum degassing, as well as the mechanical and creep behaviors of the resulting forged products. Additionally, SdF produced a prototype FB2 rotor using a conventional process. FB2, a 10% Cr steel containing cobalt and boron but lacking tungsten, emerged from the COST 522 program as the best candidate for scaling up from a laboratory experiment to a full-sized industrial component. Notably, the addition of boron effectively improved the microstructure's stability and consequently enhanced the creep resistance of these new, advanced martensitic steels. Finally, the paper will present updates on the long-term characterization program for the FB2 steel trial rotor.

A 9% Cr steel containing cobalt and boron, X13CrMoCoVNbNB9-2-1, has been manufactured by electroslag remelting (ESR) to evaluate its performance and to compare its creep strength and microstructure to a forging made from electroslag hot-topping ingot. The evaluation results confirm that it is possible to produce rotor forgings with homogeneous composition and good properties by the ESR process. The results of creep rupture tests up to 5000 h indicate that the creep strength of the forging made from ESR ingot is similar to that of the forging produced by the electroslag hot-topping process. Martensitic lath microstructures with high density dislocations and the precipitations of M 23 C 6 , VX, NbX and M2X are observed after the quality heat treatments at the center portion of both forgings. There is no large difference in the martensitic lath widths, distributions, and sizes of those particles between both trial forgings.

Monoblock low-pressure (LP) turbine rotor shaft forgings for nuclear power plants have been produced from up to 600 ton ingots. However, ingots greater than 600 tons are necessary to increase the generator capacity. Segregation, non-metallic inclusions, and micro porosities inevitably increase with the increase in ingot size. Manufacturing such massive ingots with high soundness is quite difficult. Thus, the development of 650 ton ingot production was carried out in 2010. The 650 ton ingot was dissected and investigated to verify its internal quality. The internal quality of the 650 ton ingot was found to be equal to that of 600 ton ingots. Subsequently, in 2011, we produced a 670 ton ingot, the world’s largest, to produce a trial LP rotor shaft forging with a diameter of 3,200 mm. Results show that the internal quality, mechanical properties, and heat stability are the same as LP rotor shaft forgings made from 600 ton ingots.