scholarly journals Effect of long-term thermal aging in heat exchange equipment of fast neutron switchgears on the structure and properties of austenitic chromium-nickel steel

2018 ◽  
Vol 61 (11) ◽  
pp. 907-913
Author(s):  
A. S. Kudryavtsev ◽  
K. A. Okhapkin
Keyword(s):  
Solid Solution ◽  
Phase Composition ◽  
Impact Strength ◽  
Chromium Carbide ◽  
Thermal Aging ◽  
Carbide Phase ◽  
Structure And Properties ◽  
Secondary Phases ◽  
Secondary Precipitates

The influence of long-term operation at 515 °C on structure and properties of 09Cr18Ni9 steel was investigated. Structure and phase composition were obtained using optical and scanning electron microscopy. The phase composition of the steel in equilibrium state was determined by thermodynamic modeling in the software package Fact-Sage. As a result of the study, it was found that during the operation at 515 °C with a duration of 195,000 h, the structure changes occurred in the 09Cr18Ni9 steel with the formation of secondary phases, initiated by the release of elements with limited solubility from the supersaturated solid solution. The following secondary precipitates in structure of the solid solution of austenite presented: Cr23C6 chromium carbide, ferrite (a), G-phase. Based on comparison of the thermodynamic modeling results and on experimental determination of the phase composition, it was established that the steel structure is in a state close to equilibrium. The mechanism of structural transformations course and sequence of the secondary phases’ formation were revealed and described. At the initial stage, chromium carbide is formed, then a-ferrite is formed near the carbides, and then G-phase is formed. Results of the tests for impact strength and static elongation have shown that the change in phase composition in process of thermal aging leads to embrittlement of the steel - a reduction in ductility and impact energy. Fractografic studies of fracture surfaces of the samples have shown that the decrease in plasticity during long-term high-temperature operation is associated with softening of the grain body and strengthening of the boundaries due to secondary precipitations of the carbide phase. As a result of this process, plastic deformation is localized in the weakened volume of the body of grain surrounded by strong boundaries. The structure evolution during prolonged heat aging has the greatest effect on impact strength. At the same time, the change in ultimate and yield stress is insignificant. The main contribution to the change in mechanical characteristics of steel is made by the secondary precipitates of the carbide phase.

scholarly journals On the Modelling of Thermal Aging through Neutron Irradiation and Annealing

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Boris Margolin ◽  
Elena Yurchenko ◽  
Vera Potapova ◽  
Valery Pechenkin
Keyword(s):  
Impact Strength ◽  
Neutron Irradiation ◽  
Thermal Aging ◽  
Tensile Tests ◽  
Pressure Vessels ◽  
Irradiation Effect ◽  
Thermal Embrittlement ◽  
P Diffusion ◽  
Material Conditions

A new method predicting long-term thermal embrittlement of steel caused by P segregation is verified. The method is based on the results of impact strength or fracture toughness tests using specimens after relatively short-term neutron irradiation followed by annealing. 2Cr–Ni–Mo–V steel used in reactor pressure vessels of WWER-1000 type is investigated in four conditions: initial condition, after thermal aging, after neutron irradiation, and postirradiation annealing. The results of impact strength and tensile tests and SEM investigation are presented. The brittle fracture features are considered for different material conditions. Calculative estimation on neutron irradiation effect on P diffusion in steels is carried out. Experimental data are reported which confirm an intense P diffusion acceleration under neutron irradiation.

Microstructural Evolution of Austenitic Stainless Steel AISI304 and AISI316 Subjected to High-Temperature Thermal Aging

2016 ◽  
Vol 857 ◽  
pp. 276-280 ◽  
Author(s):  
Hak Min Lee ◽  
Chung Seok Kim
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Microstructural Evolution ◽  
Thermal Aging ◽  
Austenitic Stainless Steels ◽  
Secondary Phases ◽  
Microstructural Changes ◽  
Long Period ◽  
Heat Treated

The purpose of this study is to investigate the microstructural evolution of austenitic stainless steels AISI304 and AISI316 subjected to thermal aging at elevated temperature. Most structural steels are generally subjected to softening of matrix when they are exposed to high temperatures for a long period of time because of the coarsening of the secondary phases and the phase transformation. The test specimens are heat-treated in electrical furnace for up to 5000 h at each predetermined aging time to simulate the degraded microstructure under high temperature. The microstructural changes in test materials have been evaluated by the optical and electron microscope in relation with twins, grains, precipitates, and phase transformation. The mechanical hardening were also discussed in terms of microstructural changes during long-term aging.

The Changes in Mechanical Properties of Austenitic Creep Resistant Steels SUPER 304H and HR3C Caused by Medium-Term Isothermal Ageing

2016 ◽  
Vol 258 ◽  
pp. 639-642 ◽  
Author(s):  
Jakub Horváth ◽  
Jiří Janovec ◽  
Michal Junek
Keyword(s):  
Mechanical Properties ◽  
Impact Strength ◽  
Power Plants ◽  
Secondary Phase ◽  
Thermal Exposure ◽  
Austenitic Steels ◽  
Secondary Phases ◽  
Initial State ◽  
The Impact

The paper presents the results of the analysis of secondary phases formed during thermal exposure in creep resistant austenitic steels of SUPER 304H and HR3C types. These steels were worldwide used for construction of the superheaters (the heat exchangers) of supercritical and ultra-supercritical (USC) coal-fired power plants. In order to accelerate precipitation processes, the steels were isothermally aged at 675 °C for 20 000 h. The investigations of the precipitates were primarily focused on the occurrence of brittle phases. Changes in mechanical properties caused by occurrence of secondary phases were documented by tensile testing and measurement of the impact strength. For comparison reasons, the impact tests of the initial state of the steels were also performed. The results showed that long-term ageing had led to the significant decrease of the impact strength. Correlation between precipitation of secondary phase and measured values of mechanical properties is shown. The influence of brittle phases on long-term durability of the degraded steel regarding its insufficient impact strength has been discussed.

An atomic resolution study of a carbide phase in platinum

1992 ◽  
Vol 50 (1) ◽  
pp. 20-21
Author(s):  
M.J. Witcomb ◽  
M.A. O'Keefe ◽  
CJ. Echer ◽  
C. Nelson ◽  
J.H. Turner ◽  
...  
Keyword(s):  
Solid Solution ◽  
Carbon Atom ◽  
Carbide Phase ◽  
Structural Changes ◽  
Critical Role ◽  
Alloy System ◽  
Atomic Resolution ◽  
Excess Carbon ◽  
Interstitial Carbon ◽  
Resolution Study

Under normal circumstances, Pt dissolves only a very small amount of interstitial carbon in solid solution. Even so, an appropriate quench/age treatment leads to the formation of stable Pt2C {100} plate precipitates. Excess (quenched-in) vacancies play a critical role in the process by accommodating the volume and structural changes that accompany the transformation. This alloy system exhibits other interesting properties. Due to a large vacancy/carbon atom binding energy, Pt can absorb excess carbon at high temperatures in a carburizing atmosphere. In regions rich in carbon and vacancies, another carbide phase, Pt7C which undergoes an order-disorder reaction was formed. The present study of Pt carburized at 1160°C and aged at 515°C shows that other carbides in the PtxC series can be produced.

Structure and properties of rails after extremely long-term operation

2020 ◽  
pp. 30-39 ◽  
Author(s):  
Yu. F. Ivanov ◽  
V. E. Gromov ◽  
V. E. Kormyshev ◽  
A. M. Glezer
Keyword(s):  
Surface Layer ◽  
Lattice Parameter ◽  
Crystal Lattice Parameter ◽  
Subgrain Structure ◽  
Structure And Properties ◽  
Term Operation ◽  
Head Section ◽  
Structure Phase ◽  
Defective Surface

The paper reveals regularities and mechanisms of structure-phase states and properties formation of of differentially hardened 100-m rails of DT 350 category after the passed tonnage of 1411 mln. tons brutto. The formation of highly defective surface layer with nanosize (40–50 nm) grain-subgrain structure of pearlite colonies and submicrocrystal (150–250 nm) structure grains with structure free ferrite is detected. The change of hardness, microhardness, crystal lattice parameter, microdistorsion level, scalar and excess dislocation density on the rails head section are analyzed. The possible mechanisms of cementite plates’ transformation at extremely long-term operation are discussed.

Effect of Chromium Carbide Introduced into a Flux Cored Wire Charge on the Structure and Properties of the Hardfacing Deposit

2020 ◽  
Vol 2020 (13) ◽  
pp. 1485-1490
Author(s):  
N. V. Kobernik ◽  
A. S. Pankratov ◽  
S. S. Sorokin ◽  
V. V. Petrova ◽  
A. L. Galinovskii ◽  
...  
Keyword(s):  
Chromium Carbide ◽  
Structure And Properties ◽  
Cored Wire

scholarly journals Biogeochemical Controls on the Potential for Long-Term Contaminant Leaching from Soils Developing on Historic Coal Mine Spoil

Soil Systems ◽  
2020 ◽  
Vol 5 (1) ◽  
pp. 3
Author(s):  
David Singer ◽  
Elizabeth Herndon ◽  
Laura Zemanek ◽  
Kortney Cole ◽  
Tyler Sanda ◽  
...  
Keyword(s):  
Coal Mine ◽  
Solid Phase ◽  
Microbial Community Composition ◽  
Toxic Metal ◽  
Soil Formation ◽  
Mineral Weathering ◽  
Mine Spoil ◽  
Secondary Phases ◽  
Undisturbed Soil

Coal mine spoil is widespread in US coal mining regions, and the potential long-term leaching of toxic metal(loid)s is a significant and underappreciated issue. This study aimed to determine the flux of contaminants from historic mine coal spoil at a field site located in Appalachian Ohio (USA) and link pore water composition and solid-phase composition to the weathering reaction stages within the soils. The overall mineralogical and microbial community composition indicates that despite very different soil formation pathways, soils developing on historic coal mine spoil and an undisturbed soil are currently dominated by similar mineral weathering reactions. Both soils contained pyrite coated with clays and secondary oxide minerals. However, mine spoil soil contained abundant residual coal, with abundant Fe- and Mn- (oxy)hydroxides. These secondary phases likely control and mitigate trace metal (Cu, Ni, and Zn) transport from the soils. While Mn was highly mobile in Mn-enriched soils, Fe and Al mobility may be more controlled by dissolved organic carbon dynamics than mineral abundance. There is also likely an underappreciated risk of Mn transport from coal mine spoil, and that mine spoil soils could become a major source of metals if local biogeochemical conditions change.

Mechanical Properties of Epoxy Adhesive Under Thermal Aging and Their Chemical Degradation Behavior

2021 ◽  
Vol 21 (8) ◽  
pp. 4444-4449
Author(s):  
Bongjin Chung ◽  
Shin Sungchul ◽  
Jaeho Shim ◽  
Seongwoo Ryu
Keyword(s):  
Mechanical Properties ◽  
Thermal Aging ◽  
Photoelectron Spectroscopy ◽  
Thermal Exposure ◽  
Chain Scission ◽  
Epoxy Adhesive ◽  
Chemical Degradation ◽  
Adhesive Properties ◽  
Noticeable Reduction

Epoxy adhesive was analyzed under long term thermal aging and mechanical properties and chemical degradation were observed by X-ray photoelectron spectroscopy (XPS). Long term thermal exposure of epoxy causes a noticeable reduction in adhesive properties. We developed a predictive model of temperature and time dependent aging. The temperature dependent aging behavior of epoxy adhesive shows good agreement with conventional Arrhenius equations. Using XPS analysis, we also discovered a correlation between chemical degradation and the adhesive properties. Decay of C–C bonding ratio induced chain-scission of epoxy adhesive; increase of total numbers of C–O and C═O induced oxidation of epoxy adhesive during thermal exposure.

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