Crept microstructures were examined in a 9 pct Cr martensitic steel with low carbon content. The steel was hot forged at 1323 K (1050 °C) followed by air cooling and then tempered at 1023 K (750 °C) for 3 hours. The tempered microstructure included numerous precipitates of MX-type carbonitrides and a small amount of M23C6-type carbides. Two groups of the MX-type particles were observed. The nanoscale MX-type precipitates appeared in the form of plate- and round-shaped particles. The plate-shaped MX-type particles were approximately 15 nm in the longitudinal direction and approximately 3 nm in thickness, and the round-shaped MX-type particles were 10 nm in diameter. In addition to the fine particles, the tempered martensite contained relatively coarse MX-type particles, which have a size of approximately 90 nm. The structural changes that occurred during the creep test were associated with an increase in the sizes of the lath and second-phase particles. Moreover, the creep was accompanied by appearance of Laves and Z-phase particles.
#1Kota Sawada(National Institute for Materials Science)H-Index: 23
#2Hideaki Kushima(National Institute for Materials Science)H-Index: 19
Last. Kazuhiro Kimura(National Institute for Materials Science)H-Index: 24
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Abstract Microstructural changes during creep at 600 °C under 70 MPa were investigated in the case of interrupted Gr.91 steel samples by taking into account the dislocation structure and Z-phase formation. The creep life monotonically increased with a decrease in the applied stress at each temperature considered in the study. However, the long-term creep life was shorter than that determined from the short-term creep data at 600 °C and 650 °C, meaning premature failure. The subgrain size gradual...
Abstract In this work 9%Cr alloys were designed supported by computational thermodynamic methods. Two sets of alloys were produced: 9%Cr alloys with 0.1%C and 0.05%C and 9%Cr alloys containing ∼0.03% Ti with 0.1%C and 0.05%C (always wt%). Microstructure investigations showed good agreement with the predicted phases of the thermodynamic modeling. The volume fraction of precipitated M 23 C 6 carbides is directly related to the carbon content of the alloys. For Ti-containing alloys the precipitatio...
Abstract Microstructure evolution was studied in a 3%Co modified P911 heat resistant steel during creep tests at 873 and 923 K to failure, which occurred in 4103 and 4743 h, respectively. The tempered martensite lath structure consisted of packets, blocks and laths. The average spacing of high-angle boundaries and the mean transverse lath size were about 1.9 μm and 360 nm, respectively. Various second phase particles precipitated upon tempering. Fine M(C, N) carbonitrides with an average size of...
Abstract The apparent activation energy for rupture life sometimes changes from a high value of short-term creep region “H” to a low value of long-term creep region “L”. This change results in overestimation of rupture life during long-term creep. This is called “premature creep failure”. Premature creep failure has been studied by the evaluation of microstructures of three kinds of Gr. 122 type steels and by paying attention to subgrains recovery of tempered martensite lath structures. Subgrain...
Changes in the structure of steel 10Kh9V2MFBR after creep tests are studied. It is shown that annealing causes inconsiderable changes in the structure of troostomartensite formed due to tempering in the head of a specimen. In the functional part of the specimen, on the contrary, the place of the initial troostomartensite is taken by coarse equiaxed subgrains; the density of the lattice dislocations decreases by an order of magnitude. The change in the microstructure in the process of creep cause...
In this paper, we consider the origin of high-temperature strength of heat-resistant steels belonging to martensitic class developed on the basis of the Fe—9%Cr alloy for the boiler pipes and steam pipelines of power plants at steam temperatures of up to 620°C and pressures to 300 atm. In addition, we give a brief information on the physical processes that determine the creep strength and consider the alloying philosophy of traditional heat-resistant steels. The effect of the chemical and phase ...
#1A. Aghajani(RUB: Ruhr University Bochum)H-Index: 9
#2Ch. Somsen(RUB: Ruhr University Bochum)H-Index: 18
Last. Gunther Eggeler(RUB: Ruhr University Bochum)H-Index: 67
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Abstract In the present study we investigate the evolution of the microstructure of a 12% Cr tempered martensite ferritic steel under conditions of long-term aging and creep (823 K, 120 MPa, t R = 139,971 h). We show how subgrains coarsen, that the close correlation between carbides and subgrain boundaries loosens during long-term creep and that the frequency of small-angle boundaries increases. All these elementary deformation processes have been discussed in short-term creep studies. The prese...
#2Karsten Durst(FAU: University of Erlangen-Nuremberg)H-Index: 33
Last. Wolfgang Blum(FAU: University of Erlangen-Nuremberg)H-Index: 34
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Three modified Cr steels were investigated for the types, sizes and volume fractions of precipitates. It is shown that precipitation of V in the form of fine M2X-particles provides high short-term creep resistance, but causes relatively fast degradation of creep resistance due to Ostwald ripening. In the later stages, precipitation of Z-phase and related phenomena accelerate the degradation.
#2John Hald(DTU: Technical University of Denmark)H-Index: 22
Abstract Precipitation of large Z-phase particles, Cr(V,Nb)N, replacing fine MX nitrides, (V,Nb)N, has recently been identified as a major cause of premature breakdown in long-term creep strength of a number of new 9–12%Cr martensitic steels. The Z-phase precipitates slowly during long-term exposure at around 650 °C accelerated by high Cr content in the steels. It appears that the nucleation process controls the precipitation rate of Z-phase. A 12%Cr steel, which had precipitated Z-phase during ...
#1Feng-Shi Yin(SDUT: Shandong University of Technology)H-Index: 1
#2Woo-Sang Jung(KIST: Korea Institute of Science and Technology)H-Index: 1
Nanosized MX precipitates in ultra-low-carbon ferritic/martensitic heat-resistant 9Cr-W-Mo-VNbTiN steels were characterized by transmission electron microscope (TEM) using carbon film replicas. The steels were prepared by vacuum induction melting followed by hot forging and rolling into plates. The plates were normalized at 1100 °C for 1 hour, cooled in air, and tempered at 700 °C for 1 hour. The results show that bimodal nanosized MX precipitates distribute densely and homogeneously in the matr...
#1Wi-Geol Seo(SNU: Sunchon National University)H-Index: 1
#2Jin-Yoo Suh(KIST: Korea Institute of Science and Technology)H-Index: 31
Last. Shi-Hoon Choi(SNU: Sunchon National University)H-Index: 27
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Abstract null null In this study, we report the microstructural development of heat-affected zone in P92 heat-resistant steel during creep deformation in cross-weld specimens with dissimilar weld joints between IN740H/P92 materials. Different specimens were prepared via the interruption of creep testing at 50, 70, and 90% of the measured creep-rupture life and were carefully examined and compared. To explain the deformation behavior, finite element analysis was performed in conjunction with soft...
#2Andreas Leineweber(Freiberg University of Mining and Technology)H-Index: 25
Laves phases with their comparably simple crystal structure are very common intermetallic phases and can be formed from element combinations all over the periodic table resulting in a huge number of known examples. Even though this type of phases is known for almost 100 years, and although a lot of information on stability, structure, and properties has accumulated especially during the last about 20 years, systematic evaluation and rationalization of this information in particular as a function...
This work aims to give a comprehensive and accurate view of those micromechanical models that have been developed over the past two decades by our research team. We hereby refer to the distinct cap...
#1Guangquan Wang(CAS: Chinese Academy of Sciences)H-Index: 1
#2Yanfen Li(CAS: Chinese Academy of Sciences)H-Index: 17
Last. Ke Yang(CAS: Chinese Academy of Sciences)H-Index: 59
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Abstract A novel 9Cr-ODS martensitic steel was designed for application in the advanced fusion reactors by reducing carbon content to an extremely low level to avoid the precipitation of M23C6 carbides and increasing manganese content to promote the martensite formation. The preliminary investigation was carried out by means of thermodynamics calculation, phase transformation measurement, microstructural observation and mechanical property testing. The results showed that the desired tempered ma...
Last. Fenggui Lu(SJTU: Shanghai Jiao Tong University)H-Index: 26
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The rupture behavior of the modified 10Cr–1Mo steel multi-layer welded joint is determined by the fine-grain zones of the weld metal adjacent to the fusion line during the long-term creep test at 620 °C. The microstructures of multi-layer weld metal before and after the creep tests were characterized in detail, and its role in creep behavior was systematically investigated. Most grain boundaries of subgrains represented the low-angle boundaries in the weld metal adjacent to the fusion line both ...
Last. Semyon Vaynman(NU: Northwestern University)H-Index: 16
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The long-term performance of current heat-resistant ferritic steels used in steam generators is primarily limited by microstructure degradation as a result of coarsening or transformation of precipitates. To improve the microstructural stability, a heat-resistant ferritic steel was designed via computational thermodynamics to exclusively contain metal carbonitride (MX) precipitates as the primary means for strengthening at elevated temperatures. The volume fraction of precipitates is 0.35 vol pc...
Last. Shi-Hoon Choi(SNU: Sunchon National University)H-Index: 27
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Abstract The microstructural factors that contribute to hardening mechanisms were investigated to explain the effect of post-weld heat treatment (PWHT) on the hardness of P92 steel in IN740H/P92 dissimilar weld joints. This study presents experimental analysis of the distribution of microstructural factors such as precipitate size, precipitate fraction, grain size and dislocation density in the heat-affected zone (HAZ) and base metal (BM) of the martensitic heat-resistant steel. Although precipi...
#1T. Sakthivel(RRC: Indira Gandhi Centre for Atomic Research)H-Index: 10
#2G. Sasikala(RRC: Indira Gandhi Centre for Atomic Research)H-Index: 1
Last. Madavan Vasudevan(RRC: Indira Gandhi Centre for Atomic Research)H-Index: 32
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Abstract Microstructure across the single-pass activated-tungsten inert gas (A-TIG) weld joint of P91 steel consisting of weld metal, heat affected zone (HAZ) and base metal were characterized using scanning electron microscopy and electron back scattered diffraction (EBSD-SEM). Prior austenite grain size, boundary misorientations angle, coincidence site lattice (CSL) boundaries, substructure size, combination of recovered and deformed structure, M23C6 precipitates size, decoration of boundaries...
In this study, to refine the microstructure and enhance the mechanical properties, thermomechanical treatment (TMT) was performed on modified 9Cr-1Mo steel. The creep deformation behavior of TMT processed steel and the steel in its normalized and tempered (NT) state were studied for different stress levels at 923 K (650 °C). Transient, secondary, and tertiary creep regimes were analyzed for both conditions of the steel based on the empirical equation \( \varepsilon = \varepsilon_{0} + \varepsilo...
