Abstract The effect of precipitation strengthening on the high-temperature creep strength of heat-resistant 15Cr steels with dual phases of ferrite and martensite was investigated. The creep rupture lifetime of the 15Cr steel at temperatures up to 1023 K was 10 times longer than that of conventional 9Cr steel (ASME Grade T92) with a tempered martensitic microstructure. The creep rupture strength of the 15Cr steel after 10,000 h at 973 and 1023 K was approximately two times higher than that of the T92 steel. The precipitates identified in the creep ruptured 15Cr steels were intermetallic compounds (Laves phase and χ-phase) and carbide (Cr23C6). In the 15Cr steels creep ruptured at high temperatures of 973 K and above, the Laves phase was precipitated in both ferritic and martensitic grains, and Cr23C6 carbide was precipitated at the grain boundaries. The 15Cr steel exhibited longer creep rupture lifetime than 9Cr steel with a tempered martensitic microstructure strengthened by carbides and carbonitrides, due to the precipitation of Laves phase and Cr23C6.
#1M. Shibuya(National Institute for Materials Science)H-Index: 3
#2Yoshiaki Toda(National Institute for Materials Science)H-Index: 12
Last. Kazuhiro Kimura(National Institute for Materials Science)H-Index: 24
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Abstract The effect of nickel and cobalt addition on the microstructure of 15 mass% chromium (15Cr) steels and their mechanical properties, such as creep strength and impact toughness, was investigated. The microstructure of 15Cr ferritic steel changes from a ferrite single phase to dual phases of ferrite and martensite by the addition of nickel, which is an austenite-stabilizing element. The creep strength and precipitation behavior of intermetallic compounds (Laves phase, χ-phase and μ-phase) ...
#1Kazuhiro Kimura(National Institute for Materials Science)H-Index: 24
#2Yoshiaki Toda(National Institute for Materials Science)H-Index: 12
Last. Kota Sawada(National Institute for Materials Science)H-Index: 23
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Abstract Long-term creep strength of material in the low-stress regime below elastic limit is difficult to predict by an extrapolation of short-term creep strength in the high-stress regime above elastic limit. Long-term creep strength of fully annealed ferrite-pearlite microstructure of low alloy Cr–Mo steel is higher than that of martensite and bainite microstructures. It is explained by lower dislocation density of fully annealed microstructure. According to the above concept, creep strength ...
Abstract A 12% Cr model steel was designed with the purpose of studying the nucleation and growth of modified Z -phase, Cr(V,Nb)N. The model alloy develops Z -phase after relatively short ageing times and contains only nitrides of Cr, V and Nb. Interferences from the presence of carbides and the development of Laves phase were avoided by keeping the C, W and Mo contents as low as possible. Transmission electron microscopy and X-ray diffraction analysis of extracted particles were used to follow ...
#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 ...
#1R. Agamennone(FAU: University of Erlangen-Nuremberg)H-Index: 2
#2Wolfgang Blum(FAU: University of Erlangen-Nuremberg)H-Index: 34
Last. J.K. Chakravartty(BARC: Bhabha Atomic Research Centre)H-Index: 22
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Abstract The microstructural evolution during creep at 923 K of four tempered martensite 9–12%Cr-steels modified with 2%W and 5%Co was quantified by electron microscopy. Coarsening of subgrains with strain towards the stress dependent steady state was confirmed. The evolution of the precipitate structure is similar with regard to M 23 C 6 (M: metallic element, X: N, C) and Laves phase (Fe,Cr) 2 (W,Mo) but differs strongly with regard to V-bearing precipitates. Low temper temperatures promote pre...
#2John Hald(DTU: Technical University of Denmark)H-Index: 22
AbstractThe literature on the behaviour of modified Z phase Cr(V,Nb)N in creep resistant martensitic 9–12%Cr steels is briefly reviewed. Ten different 9–12%Cr steels were investigated after prolonged exposure at 600–660°C; the modified Z phase was found in all of them. In steels with high Cr content (11–12%), Z phase precipitates much faster than in 9%Cr steels. Precipitation of Z phase is associated with dissolution of MX carbonitrides, and causes a breakdown in long term creep strength in 9–12...
#1Yoshiaki Toda(National Institute for Materials Science)H-Index: 12
#2Hideaki Tohyama(TITech: Tokyo Institute of Technology)H-Index: 2
Last. Fujio Abe(National Institute for Materials Science)H-Index: 52
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Influences of chemical compositions, heat treatment and microstructure on impact toughness of 15Cr ferritic steel have been investigated. Charpy impact values of the furnace cooled steels were lower than 15J/cm2 at room temperature independent of chemical compositions. Drastic improvement in impact toughness has been attained by controlling the carbon and nitrogen contents, by the addition of nickel and by the increase in cooling rate after annealing. However, the effect of nickel on impact toug...
Last. Fujio Abe(National Institute for Materials Science)H-Index: 52
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Effects of W and Co on creep deformation and microstructure of fully annealed and precipitation strengthened 15Cr-3W ferritic steels at 923 and 973 K have been investigated, and the strengthening effects of W and Co in a long-term and high temperature service condition have been discussed. The effect of Co addition on the creep rupture strength of the steels is higher than that of the further addition of W in the short-term. However, the creep rupture life of the steel with 6 mass% W is longer t...
#1Yoshiaki Toda(National Institute for Materials Science)H-Index: 12
#2Kazuhiro Seki(TITech: Tokyo Institute of Technology)H-Index: 3
Last. Fujio Abe(National Institute for Materials Science)H-Index: 52
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Effects of W and Co on microstructure of Co free 0.1C-15Cr-1 Mo-3W-0.2V-0.05Nb-0.07N-0.003B (mass%) steel has been investigated, and a correlation between microstructure and creep strength property has been discussed. Time to rupture of 6W-3Co steel, in which W content was increased from 3 to 6 mass% and 3 mass%Co was added, was about 100 times longer than that of 3W-0Co base steel at 923 K-100 MPa and was almost the same as that of the conventional tempered martensitic creep resistant steel of ...
#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...
#1Jakub Cieslak(AGH University of Science and Technology)H-Index: 13
Abstract Experimental (neutron and X-ray diffraction, Mossbauer spectroscopy, vibrating sample magnetometry) and theoretical (electronic structure calculations using self-consistent Korringa-Kohn-Rostoker Green's function method) studies were performed on a series of intermetallic σ-phase FeNiV compounds in systematic way. The replacement of iron by nickel was found to be the reason of a reduction in the size of the unit cell, moreover nickel atoms substitute for iron atoms on particular sites w...
#1Yoshiaki Toda(National Institute for Materials Science)H-Index: 12
#2Yuki Nakamura(Yokohama National University)H-Index: 3
Last. Osamu Umezawa(Yokohama National University)H-Index: 17
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Abstract To clarify the effects of the Fe2W Laves phase and Cr23C6 carbide on the creep strength of a new ferritic heat-resistant steel with the ferrite parent phase strengthened by intermetallic compounds and carbonitrides, the creep strength at 973 K and microstructure of the ternary Fe–15Cr-(6, 9)W alloys and the quaternary Fe-0.05C–15Cr-(6, 9)W alloys (mass%) were investigated. Increasing the amount of Laves phase precipitates by increasing the tungsten content was effective in improving the...
Last. S. Suresh Babu(UT: University of Tennessee)H-Index: 76
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Abstract The Fe–Cr–Al–Nb ferritic alloys strengthened by A2B Laves phases, with superior oxidation and corrosion resistance, are being considered for high temperature operation within fossil-fired steam power plants to increase process efficiency and reduce CO2 emissions. In this study, new sets of alloys based on Fe–30Cr–3Al–1Nb (in weight percent) were designed with (i) a high microstructural stability of Laves phase precipitates in a BCC-Fe matrix and (ii) reduced precipitate free zones along...
Abstract The design of ultra-high purity (UHP) Fe-based alloys for advanced ultra-supercritical (A-USC) technology is suggested in this work. The creep testing at 700 °C and a stress level of 150 MPa have been performed in air. The addition of small amount of reactive-elements, W, Nb, Zr and Sc, has been undertaken into model alloys with the intention to promote the precipitation strengthening. Optimizing the chemical composition coupled by pre-straining enabled improving the creep resistance; h...
Abstract A detailed characterization of the composition and evolution of precipitates during thermal exposure (0–10000 h at 650 °C) of T92 steel was carried out using a combination of transmission electron microscopy (TEM), high angle annular dark field (HAADF) imaging, energy-dispersive X-ray spectrometry (EDS) analysis, scanning electron microscopy (SEM) and first-principles calculations. It is shown that MX in T92 steel can be expressed as V/Nb(C,N) rather than complete solid-solution (V,Nb)(...
Abstract Sufficient available energy in combination with lowest environmental pollution is a basic necessity for a high standard of living in every country. To guarantee power supply for future generations, it is necessary to use fossil fuels as efficiently as possible. This fact calls for the need of power plants with improved technologies to achieve higher efficiency combined with reduced environmental impact. To realize this goal, it is not only a challenge for power station manufacturers, bu...
Last. Udochukwu Mark(Federal University of Technology Owerri)H-Index: 4
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The fact that the microstructure of steel depends on its composition and the heat treatment given to it has been heavily exploited in the design of steel for power plant applications. To obtain a steel that can function at the higher temperature where power plants operate without failure for extended life, heat treatment is needed to produce fine and highly stable dispersion of carbides, nitrides, and intermetallic compounds in the microstructure of the material. A significant contribution also ...
