Search Results for solution strengthening

The Chinese power industry has experienced rapid development in the past decade. The newly built 600+°C ultra-super-critical (UCS) fossil fire power plants and pressed water reactor nuclear power plants in China are the world’s most advanced level technically and effectively. The available capacity of 600+°C UCS fossil fire power plant in China is more than 200 GW by the end of 2015, which has greatly contributed to the energy-saving and emission-reduction for China and the whole world. In China, the 610°C and 620°C advanced USC (A-USC) fossil fire power plants had been combined into the grid, 630°C A-USC fossil fire power plant is about to start to build, the feasibility of 650°C A-USC fossil fire power plant is under evaluation, 700°C AUSC fossil fire power plant has been included in the national energy development plan and the first Chinese 700°C A-USC testing rig had been put into operation in December 2015. The advanced heat resistant materials are the bottlenecking to develop A-USC fossil fire power plant worldwide. In this paper, the research and development of candidate heat resistant steels and alloys selected and/or used for 600+°C A-UCS fossil fire power plant in China is emphasized, including newly innovated G115 martensitic steel used for 630°C steam temperature, C-HRA-2 fully solid-solution strengthening nickel alloy used for 650°C steam temperature, C-HRA-3 solid-solution strengthening nickel alloy used for 680°C steam temperature, 984G iron-nickel alloy used for 680°C steam temperature, C-HRA-1 precipitation hardening nickel alloy and C700R1 solid-solution strengthening nickel alloy used for 700+°C steam temperature.

Advanced power systems that operate at temperatures higher than about 650°C will require nickel-base alloys in critical areas for pressure containment. Age-hardened alloys offer an additional advantage of reduced volume of material compared with lower strength solid solution-strengthened alloys if thinner tube wall can be specified. To date, the only age-hardened alloy that has been approved for service in the time dependent temperature regime in the ASME Boiler and Pressure Vessel Code is INCONEL alloy 740H. Extensive evaluation of seamless tube, pipe, and forged fittings in welded construction, including implant test loops and pilot plants, has shown the alloy to be fit for service in the 650-800°C (1202-1472°F) temperature range. Since, nickel-base alloys are much more expensive than steel, manufacturing methods that reduce the cost of material for advanced power plants are of great interest. One process that has been extensively used for stainless steels and solution-strengthened nickel-base alloys is continuous seam welding. This process has rarely been applied to age-hardened alloys and never for use as tube in the creep-limited temperature regime. This paper presents the initial results of a study to develop alloy 740H welded tube, pipe and fittings and to generate data to support establishment of ASME code maximum stress allowables.

Boron and nitride additions are emerging as a promising design concept for stabilizing the microstructure of creep-resistant martensitic high-chromium steels. This approach, known as MarBN steel (martensitic steel strengthened by boron and nitrogen), combines the benefits of solid solution strengthening from boron with precipitation strengthening from nitrides. However, initial welding trials revealed challenges in achieving a uniform fine-grained region in the heat-affected zone (HAZ), which is crucial for mitigating Type IV cracking and ensuring creep strength. Despite these initial hurdles, preliminary creep test results for welded joints have been encouraging. This study presents an improved MarBN steel formulation and its investigation through uniaxial creep tests. Base material and welded joints were subjected to creep tests at 650°C for up to 25,000 hours under varying stress levels. The analysis focused not only on the creep strength of both the base material and welded joints but also on the evolution of damage. Advanced techniques like synchrotron micro-tomography and electron backscatter diffraction were employed to understand the underlying creep damage mechanisms. By combining long-term creep testing data with 3D damage investigation using synchrotron micro-tomography, this work offers a novel perspective on the fundamental failure mechanisms occurring at elevated temperatures within the HAZ of welded joints in these advanced steels.

Long-term performance of high temperature alloys is critically linked to the oxidation behavior in power generation applications in wet air and steam. As power generation systems move towards higher efficiency operation, nextgeneration fossil, nuclear and concentrating solar power plants are considering supercritical CO 2 cycle above 700°C. Wrought solid solution strengthened and precipitations strengthened alloys are leading candidates for both steam and Supercritical CO 2 power cycles. This study evaluates the cyclic oxidation behavior of HAYNES 230, 282, and 625 alloys in wet air, flowing laboratory air, steam and in 1 and 300 bar Supercritical CO 2 at ~750°C for duration of 1000 -10,000h. Test samples were thermally cycled for various times at temperature followed by cooling to room temperature. Alloy performances were assessed by analyzing the weight change behavior and extent of attack. The results clearly demonstrated the effects of alloy composition and environment on the long-term cyclic oxidation resistance. The extents of attack varied from alloy to alloy but none of the alloys underwent catastrophic corrosion and no significant internal carburization was observed in supercritical CO 2 . The performance of these alloys indicates that these materials are compatible not only in oxidizing environments, but also in Supercritical CO 2 environments for extended service operation.

The A-USC technology is still under development due to limited number of materials complying with the requirements of high creep strength and high performance in highly aggressive corrosion environments. Development of power plant in much higher temperatures than A-USC is currently impossible due to the materials limitation. Currently, nickel-based superalloys besides advanced austenitic steels are the viable candidates for some of the A-USC components in the boiler, turbine, and piping systems due to higher strength and improved corrosion resistance than standard ferritic or austenitic stainless steels. The paper, presents the study performed at 800 °C for 3000 hours on 3 advanced austenitic steels; 309S, 310S and HR3C with higher than 20 Cr wt% content and 4 Ni-based alloys including: two solid-solution strengthened alloys (Haynes 230), 617 alloy and two (γ’) gamma - prime strengthened materials (263 alloy and Haynes 282). The high temperature oxidation tests were performed in water to steam close loop system, the samples were investigated analytically prior and after exposures using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectrometry (EDS), and X-Ray Diffractometer (XRD). Mass change data have been examined every 250 hours.

A new 18Cr-9Ni-Nb-V-W-N-low C austenitic boiler tube (XA704) has been developed. Conventional high-strength austenitic stainless steel boiler tubes usually have high susceptibility to intergranular corrosion because of their high carbon content, and require special care for heated sections such as weld joints. Generally, when the carbon content decreases, the intergranular corrosion resistance improves, while the creep strength reduces. However, the creep strength of the developed steel is very high despite lower carbon content in comparison to conventional austenitic boiler tubes. The high temperature strength and the intergranular corrosion resistance of the steel are superior to those of conventional 18Cr steels such as TP347H. This excellent creep strength of XA704 is mainly due to precipitation strengthening by CrVN, and solid solution strengthening by tungsten and nitrogen. Matching welding consumables for the developed steel have also been developed. Thus, newly developed XA704 is a promising material for superheater and reheater tubes for the “600°C generation” of USC boilers. XA704 has already been used in six power plants in Japan. Currently, the steel is being standardized in the ASME Code.

Nimonic 80A, a Ni-base superalloy mainly strengthened by Al and Ti to form γ'-Ni 3 (Al, Ti) precipitation in Ni-Cr solid solution strengthened austenite matrix, has been used in different industries for more than half century (especially for aero-engine application). In consideration of high strengths and corrosion resistance both Shanghai Turbine Company (STC) has adopted Nimonic 80A as bucket material for ultra-super-critical (USC) turbines with the steam parameters of 600°C, 25MPa. First series of two 1000MW USC steam turbines made by Shanghai Turbine Co. were already put in service on the end of 2006. Large amount of Nimonic 80A with different sizes are produced in Special Steel Branch of BAOSTEEL, Shanghai. Vacuum induction melting and Ar protected atmosphere electro-slag remelting (VIM+PESR) process has been selected for premium quality high strength Nimonic 80A. For higher mechanical properties the alloying element adjustment, optimization of hot deformation and heat treatment followed by detail structure characterization have been done in this paper. The Chinese premium quality high strength Nimonic 80A can fully fulfill the USC turbine bucket requirements.

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.

High Cr ferritic steels have been developed for the large components of fossil power plants due to their excellent creep resistance, low thermal expansion, and good oxidation resistance. Development works to improve the operating temperature of these steels mainly focused on the high mechanical properties such as solid solution strengthening and precipitation hardening. However, the knowledge of the correlation between Laves phase precipitation and oxidation behavior has not clarified yet on 9Cr ferritic steels. This research will be focused on the effect of precipitation of Laves phase on steam oxidation behavior of Fe-9Cr alloy at 923 K. Niobium was chosen as the third element to the Fe- 9Cr binary system. Steam oxidation test of Fe-9Cr (mass%) alloy and Fe-9Cr-2Nb (mass%) alloy were carried out at 923 K in Ar-15%H 2 O mixture for up to 172.8 ks. X-ray diffraction confirms the oxide mainly consist of wüstite on the Fe-9Cr in the initial stage while on Nb added samples magnetite was dominated. The results show that the Fe-9Cr- 2Nb alloy has a slower oxidation rate than the Fe-9Cr alloy after oxidized for 172.8 ks

Understanding of the thermomechanical processing that affects microstructures is important to develop new alloys, because the mechanical properties of Ti alloys depend on the microstructures. In our previous study, we found Sn deteriorated the oxidation resistance, while Nb improved the oxidation resistance. Then, we have focused on Ti-Al-Nb-Zr alloys which Nb was added instead of Sn. Zr was added for solid solution strengthening. In this study, the formation of microstructures by thermomechanical processing and the effect of microstructure on the mechanical properties were investigated using the Ti-13Al-2Nb-2Zr (at%) alloy. The samples heat-treated in the β+α phase followed by furnace cooling after processed in the β+α phase formed the equiaxed or the ellipsoid α phase surrounded by the β phase. On the other hand, the sample heat-treated in the β+α phase followed by furnace cooling after processed in the β phase formed the lamellar microstructure. The compression strengths of the equiaxed α structure processed at two temperatures in the β+α phase were almost the same. While creep life of the bi-modal structure was drastically changed by processing temperature.

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.

Trials have been performed to study the enhancement of the high temperature strength of alloy 617 by utilizing the solid solution strengthening effects of tungsten additions in the amounts of 3.30 weight % and 5.61 weight %. It could be successfully demonstrated that with the 5.61 wt.% tungsten addition, the resultant mechanical high temperature properties in the range of 700 to 750 °C were far superior to standard alloy 617. Also with regard to the oxidation resistance behavior, tungsten alloyed alloy 617 exhibited superior behavior to tungsten free standard alloy 617. Only in the hot corrosion simulated tests, the tungsten containing alloys showed increasing disadvantage with increased tungsten content. However in the real world under actual service conditions, this is of lesser relevance because the gas turbine components are and could be protected by TBC (thermal barrier coatings) and/or MCrAlY coatings. This paper describes the results of these developments. Very recent data generated on the aging response indicates drastic loss in impact values on the tungsten modified alloys after aging at 3000 hours and 5000 hours at 700°C and 750°C.

The effect of Cr content on the creep strength at 650°C was examined with high Cr heat resistant steels for the USC high-temperature rotor shafts. The amount of Cr was varied from 8.5% to 11.5%, and then, the alloying effect of Cr was investigated on the stability of the precipitates at 650°C. Within the present range of the Cr content, the short-term creep rupture life under the higher applied stress increased with the Cr content in the steels, whereas the long-term creep rupture life under the lower applied stress decreased with the Cr content in the steels. For example, under the applied stress of 98MPa, the 9%Cr steel exhibited the longest creep rupture life among the experimental steels. Also, it was found from the experiment using the extracted residues that the degree of solution strengthening and the sorts of precipitates scarcely changed regardless of the Cr content in the steels. The Laves phase precipitated finely in the lath was enlarged in the 11.5%Cr steel even after a short-term creep. This result indicates that the coarsening of precipitates such as the Laves phase promotes the recovery of the lath in the early stage of creep deformation. It was suggested that 9%Cr is desirable content in the ferritic steel for suppressing the degradation of creep strength in 98MPa at 650°C.

Creep-rupture experiments were conducted on candidate Ultrasupercritical (USC) alloy tubes to evaluate the effects of cold-work and recrystallization during high-temperature service. These creep tests were performed by internally pressurizing cold-bent boiler tubes at 775°C for times up to 8000 hours. The bends were fabricated with cold-work levels beyond the current ASME Boiler and Pressure Vessel (ASME B&PV) Code Section I limits for austenitic stainless steels. Destructive metallographic evaluation of the crept tube bends was used to determine the effects of cold-work and the degree of recrystallization. The metallographic analysis combined with an evaluation of the creep and rupture data suggest that solid-solution strengthened nickel-based alloys can be fabricated for high-temperature service at USC conditions utilizing levels of cold-work higher than the current allowed levels for austenitic stainless steels.

Significant research efforts are underway in Europe, Japan, and the U.S. to develop the technology to increase the steam temperature in fossil power plants in order to achieve greater efficiency and reduce the amount of greenhouse gases emitted. The realization of these advanced steam power plants will require the use of nickel-based superalloys having the required combination of high-temperature creep strength, oxidation resistance, thermal fatigue resistance, thermal stability, and fabricability. Haynes 230 and 282 alloys are two materials that meet all of these criteria. The metallurgical characteristics of each alloy are described in detail, and the relevant high-temperature properties are presented and discussed in terms of potential use in advanced steam power plants.

Driven mainly by the environmental and economic concerns, there is an urgent need for increasing the thermal efficiency of fossil fuel power generation plants, which still languishes at around 32% under current practices. Several programs have been undertaken worldwide to address this issue. One of the immediate options is to increase the steam temperature and pressure (to the supercritical range). However, the current power plant materials appear to have inadequate creep resistance under these demanding conditions along with corrosion/oxidation problems. Hence, to meet these challenges a variety of new steels and stainless steels have been developed in the United States, Japan, and Europe. Alloy design and microstructural design approaches in developing these alloys (ferritic/martensitic, austenitic and oxide-dispersion- strengthened steels) will be briefly reviewed. Further, this paper presents creep data of these steels found in the literature in terms of Larson-Miller parameters (LMP). A detailed account of plausible creep micromechanisms in these advanced steels is also be summarized.

For future carbon neutral society, a novel thermal power generation system with no CO 2 emission and with extremely high thermal efficiency (~ 70 %) composed of the oxygen/hydrogen combustion gas turbine combined with steam turbine with the steam temperature of 700°C is needed. The key to realize the thermal power plant is in the developments of new wrought alloys applicable to both gas turbine and steam turbine components under higher temperature operation conditions. In the national project of JST-Mirai program, we have constructed an innovative Integrated Materials Design System , consisting of a series of mechanical property prediction modules (MPM) and microstructure design modules (MDM). Based on the design system, novel austenitic steels strengthened by Laves phase with an allowable stress higher than 100 MPa for 10 5 h at 700°C was developed for the stream turbine components. In addition, for gas turbine components, novel solid-solution type Ni-Cr-W superalloys were designed and found to exhibit superior creep life longer than 10 5 h under 10 MPa at 1000°C. The superior long-term creep strengths of these alloys are attributed to the “grain-boundary precipitation strengthening (GBPS)” effect due to C14 Fe 2 Nb Laves phase and bcc α 2 -W phase precipitated at the grain boundaries, respectively.

In this paper, the microstructural evolution of P92 steel were studied in the viewpoint of degradation mechanism based on the creep rupture experiment results obtained at elevated temperature by means of macroscopic, metallographic, electronic microscope, energy spectrum, XRD and TEM examination. The results show that the decrease of mechanical properties of P92 steel is mainly due to the change of microstructure and the transformation of carbides, and there is definite relationship between microstructure evolution, mechanical properties and life loss of P92 steel. The results are beneficial to the further study of mechanism of high temperature creep rupture strength and microstructural evolution of heat-resistant steel. It also has important instructive significance to quantitative identification of scientific selection of materials.

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

This study investigates how temperature affects the plasticity and thermal creep behavior of 347H stainless steel under uniaxial tension. The research combined experimental testing with advanced computational modeling. Two types of experiments were conducted: uniaxial tensile tests at temperatures from 100°C to 750°C using strain rates of ~10⁻⁴ s⁻¹, and creep tests at temperatures between 600°C and 750°C under various stress levels. These experimental results were used to develop and validate a new integrated mechanistic model that can predict material behavior under any loading condition while accounting for both stress and temperature effects. The model was implemented using a polycrystalline microstructure simulation framework based on elasto-viscoplastic Fast Fourier Transform (EVPFFT). It incorporates three key deformation mechanisms: thermally activated dislocation glide, dislocation climb, and vacancy diffusional creep. The model accounts for internal stress distribution within single crystals and considers how precipitates and solute atoms (both interstitial and substitutional) affect dislocation movement. After validation against experimental data, the model was used to generate Ashby-Weertman deformation mechanism maps for 347H steel, providing new insights into how microstructure influences the activation of different creep mechanisms.