bluuebunny/crossref_metadata_2025 huggingface dataset:
Taking into account aspects of the social being of students as a key form of pedagogical control in the organization of the educational process in the extreme conditions of the state of war
Authors: Omelchuk O.V. , Matviіenko Mykhailo
Published: March 2024

The purpose of the study was to clarify the results of the first stage of the system of research on the peculiarities of the organization of the educational process in extreme conditions of military rule. The main tasks were: to carry out an analysis of pedagogical and psychological scientific sources regarding the main characteristics of research on the control of educational activities in conditions of psychological stress; present the first stage of empirical research and present for discussion the problematic issues of studying the social conditions of students and their influence on the educational process in situations of martial law and remote and extreme forms of education.

The work sheds light on the authors' interpretation of the meaning of the concepts "extreme situation", "state of emergency" and points out their views on the study of psychological states in such conditions.

The novelty of the study should be considered the forms and methods of research and methodical implementation proposed by the authors regarding taking into account the psychological states of students and their influence on the educational process with the further use of their results in pedagogical control and the process of developing methodological recommendations.

The conclusions indicate the expediency of taking into account the social conditions and psychological states of the subjects of the educational process in various formats and methods of pedagogical control. It is emphasized that such aspects create the effect of psychological support, the formation of trust in the teacher, which in turn affects the quality of the educational process.
Students Attitudes Towards the Organization of Physical Education Classes in the Preparatory Medical Group within Ukrainian Higher Education Institutions
Authors: Sorokolit Nataliia , Kukhar Mariana
Published: March 2024

This article aims to investigate the attitudes of 1st- and 2nd-year students towards the recommendation of participating in joint physical education classes between the preparatory medical group and the main medical group, led by a single instructor. The research involves analyzing literature, surveying students through questionnaires, and mathematically processing the survey results. The study reveals distinct preferences among students of different medical groups in higher education institutions. Results from a survey of 363 students indicate a demand for joint physical education classes for both basic and preparatory medical groups. However, there is a notable difference in opinions, with 48.58% of the main medical group fully supporting the recommendation, while 36.17% of preparatory medical group students find it preferable to have separate classes. The study concludes that students in the main medical group exhibit a positive attitude towards joint classes, while preparatory medical group students express concerns about inadequate attention, discomfort, and a potential decrease in motivation. Informal conversations with preparatory medical group students reveal a perceived lack of tailored programs for their specific needs. The article suggests the necessity of individualized approaches for each medical group to enhance the effectiveness of physical education programs, improve class quality, and elevate the overall physical development, fitness, and health of students. This, in turn, is anticipated to facilitate a smooth transition of students from the preparatory group to the main medical group.
Localized osteophytic changes in the thoracic vertebra: an osteological and cadaveric study
Authors: Afroze Mookane K. H. , Sangeeta M. , Varalakshmi K. L. , Anusha R. , Jesima Preethi A.
Published: March 2024

Vertebral spinal osteophytes remain an urgent problem for clinicians of various specialties due to the fact that they can cause problems with food consumption, breathing, and sometimes cause compression of blood vessels and spinal cord. Clinical presentations encompass pain, often radiating, reduced function, stiffness, tenderness in the joints, limited movement, nerve compression, and bone pressing against tissues. Vertebral osteophytes are frequently observed in cadaveric anatomy and skeletal remains. Many instances go untreated or undetected. Several cross-sectional and prospective studies have been conducted and published concerning the cervical and lumbar spine. The current study was carried out to observe the incidence of osteophytes in the thoracic vertebrae and to document their frequency of distribution and prevalence. To study the frequency of distribution of thoracic osteophytes was reviewed in 25 cadavers (over a period of 5 years) & 188 dry thoracic vertebras (T1-T12) of south Indian population of unknown age & sex at the Department of Anatomy, MVJ MC& RH, Bangalore. The study meticulously enumerates the positions of osteophytes across different thoracic levels, aiming to investigate and understand their recurrence patterns. Incidence was expressed in terms of frequency and percentage. Incidence of osteophytes was documented in 6 cadavers and 33 dry bones which accounts for 24 % and 17.6 % respectively. Out of these, majority of them were recognized on to right side than on left side of the vertebras. The frequency of osteophytes was most commonly seen at mid thoracic level (T4-T8) followed by T9, T10 and T2. The data we received allow us to form an idea not only about the prevalence of vertebral spinal osteophytes in general, but also about the specific features of their location. Knowledge regarding the thoracic osteophytes is further required for detailed study along with dry bones. A comparative analysis of the prevalence of vertebral spinal osteophytes among people of different specialties, different ethnicities and age groups is important in further research, which will complement the obtained results.
700°C A-USC Technology Development in Japan
Authors: Fukuda M. , Yoshida T. , Iseda A. , Semba H. , Saito E. , Kitamura M. , Dohi T. , Aoki H. , Muroki K. , Fukutomi H. , Sato K. , Takahashi K. , Saito N. , Hirakawa Y. , Nishii T. , Takahashi T. , Takano T. , Matsubara Y. , Yagi Y.
Published: March 2024

Since 2008, Japanese boiler, turbine and valve manufacturers, research institutes and utility companies have been working together to develop 700V A·USC technology, with support from the Japanese government. The key areas of discussion are technology development of high temperature materials such as nickel-based alloys and advanced 9Cr steels, and their application to actual power plants. At the EPRI conference in 2013, our report mainly focused on the development of fundamental material and manufacturing technology during the first five years of the project, and the preparation status of the boiler component test and turbine rotor test for the latter four years of the project. The boiler component test, using a commercially-operating boiler, began in May 2015 and is scheduled to be finished by the end of 2016. The turbine rotor test at 700°C with actual speed will be carried out from September 2016 to March 2017. At this year’s conference, we will: l) briefly summarize the development of fundamental material and manufacturing technology and 2) provide an update on the progress of the boiler component test and the turbine rotor test.
Material and Design Aspects for Modern Steam Power Plants
Authors: Kern Torsten-Ulf , Almstedt Henning
Published: March 2024

There are main drivers for the design and assessment of steam turbine components of today such as demands for improved materials, higher plant cycling operation, and reduced life-cycle costs. New materials have been developed over the last decades resulting in advanced martensitic 9-10CrMoV steels already applied in different types of turbines successfully. Heavy cyclic loading getting more importance than in the past results in utilization of the fatigue capabilities at high and low temperatures which might lead to crack initiation and subsequent crack propagation. Fracture mechanics methods and evaluation concepts have demonstrated their applicability to assess the integrity of components with defects or crack-like outage findings. Based on realistic modelling of the failure mechanism, accurate prediction of crack sizes at failure state can be improved defining the appropriate damage criteria. Ductility is a main aspect for robust design but its value definition can depend on component type, design rules, real loading conditions, service experience, and material characteristics. The question which direct material parameter is able to serve as limit value in design and how it can be determined has to be solved. Examples of advanced analysis methods for creep crack growth and fatigue interaction involving the crack initiation time show that the reserves of new martensitic 9-10Cr steels in high temperature application can be well quantified. The creep rupture elongation Au and the loading conditions in the crack far field are main factors. If the Au value is sufficient high also after long-time service, the material remains robust against cracks. Investigations into the influence of stress gradients on life time under fatigue and creep fatigue conditions show that e.g. for 10CrMoWV rotor steel crack growth involvement offers further reserves. The consideration of constraint effect in fracture mechanics applied to suitable materials allows for further potentials to utilize margin resulting from classical design. The new gained knowledge enables a more precise determination of component life time via an adapted material exploitation and close interaction with advanced design rules.
Creep Degradation Assessment of Ni-Based Alloys by Hardness Method
Authors: Masuyama Fujimitsu , Ishiyama Kazuki , Yamaguchi Tomiko
Published: March 2024

The creep degradation/life assessment for high temperature critical component materials is absolutely needed to assure the long-term service operation and there is little experience with the service exposure of the high temperature components made of newly developed Ni-based alloys. In this study, therefore, the creep degradation assessment study on the Ni-based alloys, Alloy 617 and HR6W was conducted based on the hardness method, because the hardness measurement is a useful and simple technique for the materials characterization for any kind of high temperature-serviced steels and alloys. As the result, it was found that the hardness was increased by not only precipitation due to thermal aging but also creep stress/strain, and there existed linear relationship between the applied stress and creep-induced hardness increase. Also the hardness scatter measured was increased along with the progress of creep hardening and damage progressing in terms of creep life consumed. Those findings suggested that the creep life assessment of Ni-based alloys would be possible by means of hardness measurement. The paper also deals with the role and perspective development of non destructive damage detecting techniques, and life assessment issues on Ni-based alloys for A-USC power applications.
Research and Development of a New Austenitic Heat-Resisting Steel SP2215 for 600-620°C USC Boiler Superheater/Reheater Application
Authors: Xie Xishan , Chi Chengyu , Yu Hongyao , Dong Jianxin , Zhang Maicang , Hu Yaohe , Yang Hui , Zhu Cheng , Song Jianxin , Zhu Qiuhua , Cui Zhengqiang , Lin Fusheng
Published: March 2024

For raising thermal efficiency and decreasing CO2 emission, China had constructed the first 600°C ultra-supercritical(USC) fossil power plant in 2006. Now more than a hundred 600°C, 1000MW USC electric power units have been put in service. Recently, China has also developed 620°C USC power units and some of them have been put in service already. Meanwhile, more than fifty 620°C USC boilers will be produced by various China boiler companies. The austenitic steels TP347H, Super304H and HR3C are routinely used for 600°C USC boilers. Among these steels, a big amount of Super304H has been used for boiler superheater/reheater components application. However, Super304H is characterized by good stress-rupture strength but poor corrosion/oxidation resistance. On the other side, HR3C is characterized by very good corrosion/oxidation resistance but lower stress-rupture strength than Super304H. Now, the China 620°C USC project needs a new austenitic heat resisting steel with high stress-rupture strength and good corrosion/oxidation resistance to fulfill the superheater/reheater tube components application requirement. A new austenitic heat resisting steel SP2215 is based on 22Cr-15Ni with certain amount of Cu and also Nb and N for multiphase precipitation (MX, Cu-rich phase, NbCrN) strengthening in Fe-Cr-Ni austenitic matrix and M23C6 carbide precipitation at grain boundaries. This SP2215 new austenitic steel is characterized by high stress-rupture strength (650°C, 105h>130MPa) and good corrosion/oxidation resistance. SP2215 austenitic steel has been commercially produced in tube product form. This SP2215 new austenitic heat-resisting steel is recommended to be used as superheater/reheater components for 620°C USC boiler application.
UNS S31035/1.4990 - A Newly Developed High Strength Heat Resistant Austenitic Stainless Steel for Advanced High Efficiency Coal Fired Power Plants
Authors: Forsberg Urban , Chai Guocai , Hernblom Johan , Peltola Timo , Darley Glenn
Published: March 2024

Energy requirements and environmental concerns have promoted a development in higher-efficiency coal fired power technologies. Advanced ultra-super critical power plant with an efficiency of higher than 50% is the target in the near future. The materials to be used due to the tougher environments become therefore critical issues. This paper provides a review on a newly developed advanced high strength heat resistant austenitic stainless steel, Sandvik Sanicro 25, for this purpose. The material shows good resistance to steam oxidation and flue gas corrosion, and has higher creep rupture strength than any other austenitic stainless steels available today, and has recently obtained two AMSE code cases. This makes it an interesting option in higher pressures/temperature applications. In this paper, the material development, structure stability, creep strength, steam oxidation and hot corrosion behaviors, fabricability and weldability of this alloy have been discussed. The conclusion is that the Sanicro 25 is a potential candidate for superheaters and reheaters in higher-efficiency coal fired boilers i.e. for applications seeing up to 700°C material temperature.
Development of High Cr Containing FeCrAl Alloys for Fossil Energy Structural Applications
Authors: Yamamoto Yukinori , Pint Bruce A. , Shassere Benjamin , Suresh Babu Sudarsanam
Published: March 2024

New Fe-base ferritic alloys based on Fe-30Cr-3Al-Nb-Si (wt.%) were proposed with alloy design concepts and strategies targeted at improved performance of tensile and creep-rupture properties, environmental compatibilities, and weldability, compared to Grade 91/92 type ferritic-martensitic steels. The alloys were designed to incorporate corrosion and oxidation resistance from high Cr and Al additions and precipitate strengthening via second-phase intermetallic precipitates (Fe2Nb Laves phase), with guidance from computational thermodynamics. The effects of alloying additions, such as Nb, Zr, Mo, W, and Ti, on the properties were investigated. The alloys with more than 1 wt.% Nb addition showed improved tensile properties compared to Gr 91/92 steels in a temperature range from 600-800°C, and excellent steam oxidation at 800°C as well. Creep-rupture properties of the 2Nb-containing alloys at 700°C were comparable to Gr 92 steel. The alloy with a combined addition of Al and Nb exhibited improved ash-corrosion resistance at 700°C. Additions of W and Mo were found to refine the Laves phase particles, although they also promoted the coarsening of the particle size during aging. The Ti addition was found to reduce the precipitate denuded zone along the grain boundary and the precipitate coarsening kinetics.
Investigation and Assessment of Stress Corrosion Cracking of Welded HR3C Superheater Pipes of the MPP3 Power Plant
Authors: Hoffmeister Hans , Bader Mirko
Published: March 2024

The mechanisms of recent cracking failures of HR3C super heater pipes of a fossil power plant in the Netherlands were investigated. Initial failure investigations showed that pitting corrosion of the sensitized HR3C initiated subsequent stress corrosion cracking (SCC). It was concluded that magnesium chloride hydrates from condensed seawater had initiated pitting corrosion as well as SCC similar to the standard ASTM G36 SCC test. By experimental application of the ASTM G36 procedure, this tentative mechanism is reproduced and confirmed by a series of laboratory tests with pure magnesium chloride as well as with synthetic seawater. It included the effects of temperature, magnesium chloride concentrations of the evaporating water and applied bending moments on cracking. As a result for the 175h testing period in MgCl2*6H2O cracking increases significantly above 100°C up to 120°C but is reduced slightly at temperatures up to 155°C. With increasing bending moments, the U-shaped test pieces revealed increasing crack depths up to total fracture of the 5mm thick sections. Lower magnesium chloride concentrations as in concentrated seawater provided identical cracking, however, to a lower extent. It is therefore concluded that the operational failure of the sensitized HR3C super heater pipes was initiated in presence of condensed seawater and followed the same mechanism as found in the experimental investigation. As a conclusion, the presence of seawater saturated air at temperatures between 100° and 155°C should be avoided.
Neutral Zone Crack and Window Opening Failure in SA213 TP347H Bent Tube
Authors: Kong Byeongook , Lee Kyongwoon , Han Jungmin , Chol Yunil , Ma Youngwha , Cha Dojin , Suk JhinIk
Published: March 2024

A longitudinal crack and window opening type failure occurred in neutral zone that is applied to least plastic deformation in the bent TP347H tube during operation. From the analysis of residual stress and plastic deformation during the tube bending, there is low creep strength and high residual stress in neutral zone as compared other regions like intrados and extrados. Therefore, failure occurred in neutral zone due to stress relaxation concentrated in grain boundary during operation.
Evaluation of Long-Term Creep Rupture Life of Gr.91 Steel by Analysis of On-Going Creep Curves
Authors: Maruyama Kouichi , Nakamura Junya , Yoshimi Kyosuke , Nagae Yuji
Published: March 2024

A methodology is developed for evaluating its creep rupture life from analysis of an on-going creep curve with the aid of an Ω creep curve equation. The method is applied to on-going creep curves of grade 91 steel for evaluating their rupture lives. Quick decrease in creep rupture strength has been reported recently in long-term creep of grade 91 steel. The quick decrease of the steel is discussed by using the rupture lives evaluated. The quick decrease is confirmed in the present study in the time range longer than 3 x 104 h at 600°C.
Investigation and Post Service Creep Testing of a Mis-Heat Treated Seam Welded Grade 91 Hot Reheat Bend
Authors: Brett S J , Kimpton S , Clark A
Published: March 2024

This paper reports the results of a collaborative investigation of an ex-service grade 91 bend carried out by the UK generating companies Centrica, SSE, Engie and RWE. As part of the handover exercise for Centrica’s Langage power station in 2009 a number of routine checks were carried out on the main steam and hot reheat grade 91 steam pipework. In some cases low hardness readings were found with subsequent metallurgical replication showing the presence of an aberrant non martensitic microstructure. This led to a more extensive inspection programme on the steam lines and the discovery of other areas of suspect material. A review of the operating capability of the plant, including detailed pipework stress analysis and a pipework peaking assessment, along with the assumption that lower strength grade 91 material was present, led to the steam lines being down rated and returning to service under these revised conditions. At the first C inspection in December 2012, after the HRSG and associated pipework had operated for 18720 hours, a bend with a soft weld, along with a section of the straight pipe on either side, was removed from service. An investigation was undertaken to establish how long this component would have survived, had it been left in service, and to consider the implications for the future operation of the plant.
Life Diagnosis and Extension of a High Temperature Heating Surface
Authors: Cao Haitao , Ma Hong , Zhang Lei , Shi Zhigang , Zheng Fangping , He Xipeng
Published: March 2024

Through inner wall oxidation scale thickness measurement, sampling tests and installation of wall temperature measuring device in the boiler, the equivalent wall temperature and its distribution of secondary high temperature reheater tube were estimated and verified, and the temperature field distribution of tube platen which is of single peak distribution in the direction vertical to tube platen and an apparent lower temperature distribution covered by the smoke shield at the side of boiler wall were both obtained. For the middlemost 10CrMo910, the wall temperature of individual tube was getting close to 600°C. Afterwards material state and residual creep life of tube platen were estimated and calculated. The results of estimate and calculation show that the tube platen in the middle is not suitable for further service due to its degraded material states and lower antioxidant ability. Thus with consideration of distribution characteristics of temperature field, parts of tube platens in the middle are proposed to be replaced with T91 tubes. Furthermore, to avoid onsite heat treatment, 10CrMo910 tube covered by the smoke shield in the boiler was reserved, and a small piece of 10CrMo910 tube was welded at the inlet and outlet ends respectively in the manufactory.
Development of Large Sand Casting of Haynes 282 for A-USC Turbine
Authors: Thangirala (Mani) Subrahmanyam , Myers James
Published: March 2024

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.
Analysis, Assessment and Processing of the Recirculation Pump Casing Damage in the Power Plant Staudinger Unit 5
Authors: Bader M. , Bagaviev A. , Kaufhold E. , Wolf H.-W.
Published: March 2024

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.
Corrosion of Nickel-Base Alloys by Supercritical CO2
Authors: Olivares R.I , Stein W. , Nguyen T.D. , Young D.J.
Published: March 2024

Nickel-base alloys were exposed to flowing supercritical CO2 (P = 20MPa) at temperatures of 700 to 1000°C for up to 1000 h. For comparison, 316L stainless steel was similarly exposed at 650°C. To simulate likely service conditions, tubular samples of each alloy were internally pressurised by flowing CO2, inducing hoop stresses up to 35 MPa in the tube walls. Materials tested were Haynes alloys 188, 230 and 282, plus HR120 and HR160. These alloys developed chromia scales and, to different extents, an internal oxidation zone. In addition, chromium-rich carbides precipitated within the alloys. Air aging experiments enabled a distinction between carburisation reactions and carbide precipitation as a result of alloy equilibration. The stainless steel was much less resistant to CO2 attack, rapidly entering breakaway corrosion, developing an external iron-rich oxide scale and internal carburisation. Results are discussed with reference to alloy chromium diffusion and carbon permeation of oxide scales.
Development of Matching Welding Consumables for Boron/Cobalt Alloyed 9%Cr-Mo Steels and the Weld Metal Properties
Authors: Zhang Zhuyao , Golding Mark , Bouillot Claude
Published: March 2024

Despite the significant progress achieved in power generation technologies in the past two decades, finding effective solutions to further reduce emissions of harmful gases from thermal power plant still remains the major challenge for the power generation industry as well as alloy material developers. In the European material programmes COST 522 and COST 536, based on the existing 9-12%Cr creep resisting steels, an advanced 9%Cr-Mo martensitic alloy, C(F)B2 (GX13CrMoCoVNbNB9-2-1) alloy has been developed. By modification through alloying of boron and cobalt and together with other micro-adjustment of the composition, C(F)B2 alloys has showed very encouraging properties. The current paper summaries the development and evaluation of the matching filler metals for C(F)B2 grade. The design of the filler metal composition is discussed and comparison is made with the parent materials in respect to the alloy additions and microstructure. The mechanical properties of the weld metals at ambient temperature are examined. Creep properties of both undiluted weld metals and cross-weld joints are examined through stress rupture test and the data are evaluated and compared with those of the base alloy and other existing 9%Cr-Mo creep resisting steels.
Microstructural Characterisation of Creep Tested 9Cr Welds for MarBN Steel
Authors: Guo J. , Jepson M. A. E. , Thomson R. C.
Published: March 2024

Creep properties of 9Cr heat resistant steels can be improved by the addition of boron and nitrogen to produce martensitic boron-nitrogen strengthened steels (MarBN). The joining of this material is a crucial consideration in the material design since welds can introduce relatively weak points in the structural material. In the present study, creep tests of a number of MarBN weld filler metals have been carried out to determine the effect of chemistry on the creep life of weld metal. The creep life of the weld metals was analysed, and the evolution of creep damage was investigated. Significant differences in the rupture life during creep have been observed as a function of boron, nitrogen and molybdenum concentrations in the weld consumable composition. Although the creep lives differed, the particle size and number in the failed creep tested specimens were similar, which indicates that there is a possible critical point for MarBN weld filler metal creep failure.
The Evolutionary Behavior of Laves Phase in Virgin FB2 Steel During Welding and Its Effect on Weld Joints
Authors: Li Kejian , Cai Zhipeng , Pan Jiluan
Published: March 2024

In 9~12% Cr containing martensitic stainless steels, Laves phase usually occurs after long term high temperature exposure, while in the present work, some sparse relatively large particles of (Fe,Cr)2Mo type Laves phase were observed in virgin FB2 steel. It is speculated that the large Laves phase particles formed in casting process due to dendritic segregation. Then the evolutionary behavior of Laves phase during welding thermal cycle was studied and constitutional liquation of Laves phase was found, suggesting a liquation crack tendency in FB2 steel. At last, the hot ductility tests showed that the area where constitutional liquation occurred would act as crack initiation site, and the tested specimen fractured without any obvious plastic deformation. This work provided some guidance for the practical production of welded turbine rotors made of FB2 steel.
Effect of Aging on Creep Strength of Grade 91 Steel Weld Metal
Authors: Nakahashi Sosuke , Yaguchi Masatsugu , Tamura Koji , Minami Yusuke
Published: March 2024

Type IV damage is observed in creep-strength-enhanced ferritic (CSEF) steel used in USC plants and the research on the evaluation of such damage has been carried out in the world. Type I failure is recently reported in welded joint of Gr.91 so that the importance of the evaluation of the creep strength of the weld metal is increasing. In this study, the change in hardness with aging and creep strength before and after aging were evaluated to determine the creep strength of the weld metal of Gr.91. The hardness of the weld metal subjected to aging significantly decreased compared with that of the base metal and the heat-affected zone (HAZ). The creep strength of the weld metal was also decreased by aging. From these results, it is suggested that the failure morphology of Gr.91 steel welded joint used for a long term may change from type IV to type I.
Assessment and Quantification of Damage in the Grade 91 Steel Partially Transformed Zone
Authors: Siefert John A. , Parker Jonathan D. , MacLachlan Ryan , Yan Sabrina , Thomson Rachel
Published: March 2024

Damage in the grade 91 steel partially transformed zone of weld heat affected zones has historically been associated with many different types of microstructural features. Features described as being responsible for the nucleation of creep damage include particles such as laves phase, coarse M23C6, inclusions, nitrides, or interactions between creep strong and creep week grains, grain boundaries and potentially other sources. Few studies have attempted to link the observations of damage on scales of increasing detail from macro, to micro, to nano. Similarly, assessments are not made on a statistically relevant basis using 2D or 3D microscopy techniques. In the present paper, 2D assessment using scanning electron microscopy (SEM) and quantification techniques such as energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) are utilized in combination with 3D serial sectioning of large volumes using plasma focused ion beam milling (P-FIB) and simultaneous EDS to evaluate an interrupted cross-weld creep test. Moreover, the sample selected for examination was from a feature cross-weld creep test made using a parent material susceptible to the evolution of creep damage. The test conditions were selected to give creep brittle behaviour and the sample was from a test interrupted at an estimated life fraction of 60%. The findings from these evaluations provide perspective on the features in the microstructure responsible for the nucleation and subsequent growth of the observed damage.
Microstructural Evaluation in Heat-Affected Zone of 9Cr-3W-3Co-Nd-B Heat-Resistant Steel
Authors: Hamaguchi Tomoaki , Kurihara Shinnosuke , Hirata Hiroyuki , Okada Hirokazu
Published: March 2024

A newly developed ferritic heat-resistant steel; 9Cr-3W-3Co-Nd-B steel has higher creep rupture strength both in the base metal and welded joints than the conventional high-Cr ferritic heat-resistant steels. The creep rupture strengths of 9Cr-3W-3Co-Nd-B steel welded joints were below the lower limit of the base metal in long-term creep stage more than 20,000 hours. The creep rupture position was heat-affected zone (HAZ) from 1.0 to 1.5 mm apart from the fusion line on the welded joint specimen ruptured at 34,966 hours. The equiaxed subgrains and coarsened precipitates were observed in HAZ of the ruptured specimen. In order to clarify the creep fracture mechanism of the welded joints, the microstructures of HAZ were simulated by heat cycle of weld, then observed by EBSD analysis. Fine austenite grains formed along the prior austenite grain boundaries in the material heated just above AC3 transformation temperature, however there were no fine grains such as conventional steel welded joints. The prior austenite grain boundaries were unclear in the material heated at 1050 °C. The creep rupture life of the material heated at just above AC3 transformation temperature exceeded the lower limit of base metal and there was no remarkable degradation, although it was shorter than the other simulated materials. It is, therefore, concluded that the creep fracture of 9Cr-3W-3Co-Nd-B steel welded joint in long-term stage occurred at HAZ heated at from just above AC3 transformation temperature to 1050 °C. It is speculated that the fine austenite grains formed along the prior austenite grain boundaries and inhomogeneous microstructures cause the coarsening precipitates and recovery of lath structure during long-term creep deformation.
Relationship of Long-Term Creep Rupture Strength between Base Metal and Weldment in Mod.9Cr-1Mo Steels
Authors: Arisue Ko , Komai Nobuyoshi , Tominaga Kimihiko , Fujita Masaaki
Published: March 2024

Long-term creep rupture tests up to 105 hours at 600℃ and 650℃ were carried out on mod.9Cr- 1Mo steel base metal and weldments from five different materials, consisting of various chemical compositions and heat treatments as well as welding conditions. As a result, positive correlations of creep rupture strength were clarified between the base metal and weldments from the same materials. Microstructural observations and thermokinetic calculations revealed that the strength correlations were attributed to the precipitation strengthening behavior of finely dispersed M23C6 carbides and V-type MX carbonitrides, where their precipitation distribution characteristic in the fine-grained HAZ microstructures partially or almost entirely took over those in base metal. This finding implies that the long-term creep rupture strength of mod.9Cr-1Mo steel weldment might be able to be evaluated as long as the corresponding base metal strength is obtained.
Martensitic Steel CPJ7 for Improved High-Temperature Creep Capabilities in Power Plants
Authors: Detrois Martin , Jablonski Paul D. , Hawk Jeffrey A.
Published: March 2024

A creep resistant martensitic steel, CPJ7, was developed with an operating temperature approaching 650°C. The design originated from computational modeling for phase stability and precipitate strengthening using fifteen constituent elements. Approximately twenty heats of CPJ7, each weighing ~7 kg, were vacuum induction melted. A computationally optimized heat treatment schedule was developed to homogenize the ingots prior to hot forging and rolling. Overall, wrought and cast versions of CPJ7 present superior creep properties when compared to wrought and cast versions of COST alloys for turbines and wrought and cast versions of P91/92 for boiler applications. For instance, the Larson Miller Parameter curve for CPJ7 at 650°C almost coincides with that of COST E at 620°C. The prolonged creep life was attributed to slowing down the process of the destabilization of the MX and M23C6 precipitates at 650°C. The cast version of CPJ7 also revealed superior mechanical performance, well above commercially available cast 9% Cr martensitic steel or derivatives. The casting process employed slow cooling to simulate the conditions of a thick wall full-size steam turbine casing but utilized a separate homogenization step prior to final normalization and tempering. To advance the development of CPJ7 for commercial applications, a process was used to scale up the production of the alloy using vacuum induction melting (VIM) and electroslag remelting (ESR), and underlined the importance of melt processing control of minor and trace elements in these advanced alloys.
Degradation Mechanism of Long-Term Creep Rupture Strength in Gr.23 (2.25Cr-1.6W) Steel
Authors: Komai Nobuyoshi , Imazato Toshiyuki , Tominaga Kimihiko , Fujita Masaaki
Published: March 2024

Creep strength degradation behavior of normalized and tempered 2.25Cr-1.6W-V-Nb(Gr.23) steel was investigated by conducting extra long-term creep rupture tests. Creep strength drop was observed in long-term creep range at 600°C and above, while signs of a creep strength drop were not identified at 550°C and 575°C. Creep strength drop of around 110 MPa at 600°C was caused not by the effect of oxidation but rather by a change of the deformation mechanism or the weakening of deformation resistance by the microstructural change during creep. The effect of oxidation was significant for causing a further creep strength drop in the range which exceeded 20,000 h in rupture time at 600°C. As a result, the creep strength at 60 MPa and 600°C was almost the same regardless of long tempered or aged steel.
Grain Boundary Design Using Precipitation of Delta-Ni3Nb Phase for Ni-Based Wrought Alloys
Authors: Kobayashi Satoru , Otsuka Tomoki , Takeyama Masao , Aoki Chuya , Ueno Tomonori
Published: March 2024

Effects of alloying additions of Ti or Mo to a simplified chemical composition of the γ′′-Ni3Nb strengthened type Ni-based alloy 718 on the precipitation mode of δ-Ni3Nb phase were investigated to aim at designing grain boundaries using the δ phase for raising temperature capability of the γ′′ strengthened Ni-based wrought alloys. In the base alloy of Ni-22Cr-16Fe-3.5Nb, the δ phase precipitated at the grain boundaries of the matrix phase in a platelet form by continuous precipitation mode at temperatures above 1273K (1000°C) but in a lamellar morphology by discontinuous precipitation mode below that temperature. The boundary temperature where the continuous/discontinuous precipitation mode changes was raised by addition of 1 % Ti and lowered by addition of 5% Mo. The increase in the boundary temperature by Ti addition can be considered to have occurred by an increase in the solvus temperature of γ′′ phase. The decrease in the boundary temperature by Mo addition can be interpreted by the reduction of the strain energy caused by the coherent γ′′ precipitates and/or the volume change by the formation of δ phase from the γ/γ′′ phases, which may promote the continuous precipitation with respect to the discontinuous precipitation.
Desulfurization Mechanism of Molten Ni-Base Superalloy Containing Al Using CaO Rod
Authors: Kishimoto Yuki , Iguchi Taketo , Kono Takaaki , Yokokawa Tadaharu , Osawa Makoto , Kawagishi Kyoko , Suzuki Shinsuke , Harada Hiroshi
Published: March 2024

It is required to reduce the lifetime cost of turbine blades. To achieve the cost reduction, a refining and recycling method of scrapped turbine blades is proposed. For the establishment of the method, desulfurization mechanism of Ni-base superalloy by solid CaO was studied. 500 g of superalloy containing sulfur was heated in a vacuum induction furnace and kept at 1600 °C. A CaO rod was inserted into the molten alloy and held for 600 s. After the experiment, sulfur content in the alloy decreased from 200 ppm to 54 ppm. On the surface of the CaO rod after the experiment, only Ca, O, Al, and S were found by EPMA analysis. Especially, Al and S were distributed at the surface and grain boundaries of the rod. By powder XRD analysis, CaO, CaS and 3CaO･Al2O3 were identified as constituent phases on the rod. The desulfurization mechanism of superalloy at 1600 °C is supposed to be three steps: (1) Al and S in the alloy react with CaO to generate CaS and Al2O3, respectively. (2) Al2O3 melts with CaO as liquid slag. (3) CaS is captured by the slag, therefore, sulfur is removed from the alloy.
Generation Behavior of Abnormally Large Grain in Superalloy 718
Authors: Aoki Chuya , Date Masayoshi , Ueno Tomonori , Ohno Takehiro , Oikawa Katsunari
Published: March 2024

The behavior of strain-induced abnormal grain growth (AGG) in superalloy 718 has been investigated using compression testing and subsequent heat treatment below the d-phase solvus temperature of 980 °C. The nuclei of AGG grains were slightly newly recrystallized grains by a nucleation because small grains without dislocation was observed in the as- deformed microstructure. AGG was caused by the difference in intragranular misorientation (related to the stored strain energy in a grain) between dynamic recrystallized grains and deformed matrix. The initiation of AGG was retarded with decreasing plastic strain and produced microstructures consisted of larger grains having more complex morphology. It was observed that grain boundary migrated locally in the direction perpendicular to, or mainly in the direction parallel to the S3 {111} twin boundaries along with the formation of high-order twins. As a result of multiple twinning, AGG grains seemed to evolve with the growing directions changed.
An Economical 1-Step Aging Treatment for Haynes 282 Superalloy—Effects on Microstructure and High-Temperature Properties
Authors: Terner Mathieu , Shin Kyeong-Yong , Kim Jin-Hyeok , Hong Hyun-Uk , Kong Byeong-Ook
Published: March 2024

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.
Characterization of Ni-Based Alloys for Advanced Ultra-Supercritical Power Plants
Authors: Chen Xiang , Tortorelli Peter , Shyam Amit , Santella Michael , Dryepondt Sebastien , Unocic Kinga A. , Lara-Curzio Edgar , Maziasz Philip
Published: March 2024

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.
Creep Damage Assessment of 47Ni-23Cr-23Fe-7W Alloy
Authors: Shioda Yoshiki , Nakagawa Hirokatsu , Nomura Kyohei , Yamazaki Naoki , Kubushiro Keiji
Published: March 2024

In order to establish a creep damage assessment method for 47Ni-23Cr-23Fe-7W (HR6W), which is a candidate material of A-USC, microstructure observation of creep interrupted specimens and ruptured specimen was conducted, and the creep damage process was examined. Creep tests were conducted under conditions of 800°C, 70 MPa, 700°C, and 100 MPa. For creep damage assessment, an optical microscope was used for replicas sampled from the outer surface of specimens, and crack ratio at grain boundaries was assessed. The results indicated that creep voids and cracks were initiated at grain boundaries from about 0.35 of creep life ratio, and crack ratio increased drastically after creep life ratio of 0.65. This crack ratio was almost the same regardless of the specimen shape Therefore, the method to assess crack ratio using replicas is considered to be an effective method for creep damage assessment of HR6W. An increase in the crack ratio due to an increase in creep life ratio showed the same trend as the change in elongation of creep interrupted specimens. Microstructure observations were conducted with interrupted specimens using SEM-ECCI (Electron Channeling Contrast Imaging) in order to clarify the cause of acceleration creep. The results showed that sub-boundary developed significantly near grain boundaries, which indicates that sub-boundary development may cause acceleration.
Study on the Test Method of Oxide Scale Adhesion inside Superheater/Reheater Tubes Based on Image Recognition
Authors: Guo Junwen , Ma Jianmin , Qiao Yue , Li Zhigang , Niu Kun , Yan Aijun , Hao Le , Wen Wu , Yan Xiaojiang
Published: March 2024

The fall-off of oxide scale with poor adhesion inside superheater/reheater tubes in boilers for (ultra) supercritical power unit is the main cause of accidents such as superheater/reheater blockage, tube explosion and solid particle erosion in the steam turbine which cause serious economic losses. However, there is still no method for testing and assessing the adhesion of oxide scale inside the tube. A method for testing the adhesion of corrosion products in tubes by spiral lines is proposed in this paper, and the accuracy of adhesion evaluation is improved by adopting the image recognition method.