Search Results for ladle furnace

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.

The development of new ferritic-martensitic steels for rotor applications was a primary focus of the joint research projects COST 501 and COST 522. During COST 501, multiple trial compositions of 9-10% chromium steels underwent comprehensive testing, with the COST 522 project ultimately selecting the most promising candidate, FB2, a 10% Cr steel containing cobalt and boron additions, notably without tungsten. Società delle Fucine (SdF) successfully produced an FB2 prototype rotor using a conventional manufacturing process involving ladle furnace and vacuum degassing techniques. A comprehensive creep test program was initiated to characterize the full-size component's properties, with results demonstrating consistency with laboratory material performance in both creep resistance and ductility. The extensive testing, which exceeded 30,000 hours, aimed to achieve a 15-20 MPa improvement over Grade 92, targeting 100,000 creep hours at 600°C. Complementing the mechanical testing, a parallel microstructural investigation program was launched to evaluate structural evolution and gain deeper insights into boron's role as a creep-strengthening element in advanced ferritic-martensitic steels.

Demand of 9-12% chromium steel rotor forgings becomes higher from point of view of environmental protection in coal fired fossil power generations. Japan Casting & Forging Corporation (JCFC) has manufactured 9-12% Cr steel rotor forgings with JCFC's original techniques since 1991. Recently, type E steel developed by European COST program has been trial melted to meet the demand of such high Cr steel forgings in the world. Full size two forgings have been manufactured from approximately 70 ton ingot applying Electro Slag Hot Topping by JCFC (ESHT-J) process. One of the trial forgings has been austenitized at higher temperature in the quality heat treatment to improve long term creep strength. Their productivities and sufficient qualities have been ascertained.

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.

Grade 91 steel has achieved broad acceptance within the modern boiler industry to fabricate a variety of critical pressure components including tubing, piping and headers, particularly in Ultra Super Critical (USC), Advanced Ultra Super Critical (A-USC) and Combined Cycle Power Plants (CCPP). The applications for which this material is used enforce severe requirements on strength, corrosion, creep properties and thermal stability during service. The properties of Creep Strength Enhanced Ferritic steels (CSEF) such as Grade 91 are critically dependent on manufacturing factors like steelmaking, heat treatments and welding: poor control of these parameters can severely compromise material properties. In scientific literature, several studies correlate low creep ductility to high content of trace elements such As, Sn, Sb, Pb, Cu, P and S. Since the current reference Codes, namely ASTM/ASME, don’t require particular restrictions for these elements, Electric Power Research Institute (EPRI) has issued guidelines for grade 91 which enforce a significant reduction of impurities and trace elements. This paper discusses steelmaking operating challenges to produce Grade 91 steel with very low contents of the above mentioned residual elements, starting from the furnaces charges, up to the chemical composition measuring equipment used in the steel shop laboratories.

Research conducted under European COST programs has demonstrated the beneficial role of boron in enhancing the microstructural stability and creep performance of new martensitic steels. The FB2 steel (a 10%Cr steel containing Co and B, without W) emerged as the most promising candidate and was successfully scaled up to a full industrial rotor component by Società delle Fucine. Extensive creep testing, now reaching 50,000 hours, indicates an improvement of 15-20 MPa over Grade 92 at 600°C for 100,000 hours. STEM and X-ray analysis of long-term aged specimens confirmed that boron significantly enhances precipitate stability compared to Grade 91 and 92 steels, validating its role as a creep-strengthening element and stabilizer of carbides and martensitic structure.

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.

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.

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.

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.