Formation of the Fe2Hf Laves Phase through Eutectoid Type Reaction of δ→γ+Fe2Hf in Ferritic Heat Resistant Steels

2015 ◽  
Vol 1760 ◽  
Author(s):  
Satoru Kobayashi
Keyword(s):  
Phase Transformation ◽  
Ferritic Steel ◽  
Laves Phase ◽  
Ferritic Steels ◽  
Microstructural Observation ◽  
Interphase Precipitation ◽  
Δ Ferrite ◽  
Term Creep ◽  
Heat Resistant Steels

ABSTRACTPeriodically arrayed rows of fine Fe2Hf Laves phase particles were found to form in 9Cr ferritic steel. Microstructural observation demonstrates that the particles were formed on cooling through the interphase precipitation on the phase transformation from the δ ferrite to the γ austenite along the eutectoid transformation route of δ → γ+Fe2Hf and subsequently a phase transformation from the austenite to the α ferrite took place. This eutectoid route is expected to be effectively used for improving the long term creep strength of ferritic steels with Laves phase.

On the formation and growth of Mo-rich Laves phase particles during long-term creep of a 12% chromium tempered martensite ferritic steel

2009 ◽  
Vol 61 (11) ◽  
pp. 1068-1071 ◽  
Author(s):  
A. Aghajani ◽  
F. Richter ◽  
C. Somsen ◽  
S.G. Fries ◽  
I. Steinbach ◽  
...  
Keyword(s):  
Ferritic Steel ◽  
Laves Phase ◽  
Tempered Martensite ◽  
Term Creep

Microstructures of Grade 91 Steels Under Long-Term Creep Conditions

2018 ◽  
Author(s):  
Kenji Kako ◽  
Susumu Yamada ◽  
Masatsugu Yaguchi ◽  
Yusuke Minami
Keyword(s):  
Remaining Life ◽  
Martensitic Steels ◽  
Creep Data ◽  
Creep Life ◽  
Creep Tests ◽  
Microstructural Observation ◽  
Type Iv ◽  
Grade 91 ◽  
Term Creep

Type IV damage has been found at several ultra-supercritical (USC) plants that used high-chromium martensitic steels in Japan, and the assessment of the remaining life of the steels is important for electric power companies. The assessment of the remaining life needs long-term creep data for over 10 years, but such data are limited. We have attempted to assess the remaining life by creep tests and by microstructural observation of Grade 91 steels welded pipes which were used in USC plants for over 10 years. Following the results of microstructural observation of USC plant pipes, we find that microstructures, especially distribution of MX precipitates, have large effect on the creep life of Grade 91 steels.

Prediction of Breakdown Transition of Creep Strength in Advanced High Cr Ferritic Steels by Hardness Measurement of Aged Structures at High Temperature

2007 ◽  
Vol 345-346 ◽  
pp. 553-556 ◽  
Author(s):  
Hassan Ghassemi Armaki ◽  
Kouichi Maruyama ◽  
Mitsuru Yoshizawa ◽  
Masaaki Igarashi
Keyword(s):  
Power Plants ◽  
Rupture Strength ◽  
Hardness Measurement ◽  
Creep Rupture ◽  
Ferritic Steels ◽  
Creep Rupture Strength ◽  
Cr Concentration ◽  
Reduction Of Area ◽  
Term Creep

Recent researches have shown the premature breakdown of creep rupture strength in long term creep region of advanced high Cr ferritic steels. As safe operation of power plants becomes a serious problem we should be able to detect and predict the breakdown transition of creep rupture strength. Some methods for detecting the breakdown transition have been presented till now like the measurement of reduction of area after creep rupture and particle size of laves phase. However it will be more economic if we make use of non-destructive tests, for example, hardness testing. In this paper 3 types of ferritic steels with different Cr concentration have been studied. The results suggest that the hardness of aged structures is constant independently of exposure time in short term region, whereas the hardness breaks down in long term region. The boundary of breakdown in hardness coincides with that of breakdown in creep rupture strength.

Novel Concept of Creep Strengthening Mechanism using Grain Boundary Fe2Nb Laves Phase in Austenitic Heat Resistant Steel

2011 ◽  
Vol 1295 ◽  
Author(s):  
Imanuel Tarigan ◽  
Keiichi Kurata ◽  
Naoki Takata ◽  
Takashi Matsuo ◽  
Masao Takeyama
Keyword(s):  
Grain Boundary ◽  
Strengthening Mechanism ◽  
Local Deformation ◽  
Creep Rupture ◽  
Laves Phase ◽  
Resistant Steel ◽  
Heat Resistant Steel ◽  
Heat Resistant ◽  
Term Creep

ABSTRACTThe creep behavior of a new type of austenitic heat-resistant steel Fe-20Cr-30Ni-2Nb (at.%), strengthened by intermetallic Fe2Nb Laves phase, has been examined. Particular attention has been given to the role of grain boundary Laves phase in the strengthening mechanism during long-term creep. The creep resistance increases with increasing area fraction (ρ) of grain boundary Laves phase according to equation ε/ε = (1−ρ), where ε0 is the creep rate at ρ = 0. In addition, the creep rupture life is also extended with increasing ρ without ductility loss, which can yield up to 77% of elongation even at ρ = 89%. Microstructure analysis revealed local deformation and well-developed subgrains formation near the grain boundary free from precipitates, while dislocation pile-ups were observed near the grain boundary Laves phase. Thus, the grain boundary Laves phase is effective in suppressing the local deformation by preventing dislocation motion, and thereby increases the long-term creep rupture strength. This novel creep strengthening mechanism was proposed as “grain boundary precipitation strengthening mechanism” (GBPS).

Inherent creep strength and long term creep strength properties of ferritic steels

1997 ◽  
Vol 234-236 ◽  
pp. 1079-1082 ◽  
Author(s):  
K. Kimura ◽  
H. Kushima ◽  
F. Abe ◽  
K. Yagi
Keyword(s):  
Creep Strength ◽  
Strength Properties ◽  
Ferritic Steels ◽  
Term Creep

Stress Driven Phase Transformations and Recrystallization Processes in Two-Phase Titanium Aluminide Alloys

2000 ◽  
Vol 652 ◽  
Author(s):  
Fritz Appel ◽  
Michael Oehring
Keyword(s):  
Phase Transformation ◽  
Titanium Aluminide ◽  
Electron Microscope Study ◽  
Phase Boundaries ◽  
Two Phase ◽  
Titanium Aluminide Alloy ◽  
Lower Solubility ◽  
Term Creep ◽  
Titanium Aluminide Alloys

ABSTRACTThe paper presents an electron microscope study of phase transformation and recrystallization in an intermetallic α2(Ti3Al) + γ(TiAl) titanium aluminide alloy, after long-term creep. The mechanisms are closely related to the atomic structure of the α2/γ phase boundaries and are probably driven by a non-equilibrium of the phase composition leading to the dissolution of the α2 phase. The α2 /γ transformation is accompanied by the formation of precipitates, because the γ(TiAl)phase has a significantly lower solubility for interstitial impurities than the α2(Ti3Al) phase.

Regulatory Review Results on Allowable Tensile Stress Values of Creep Strength Enhanced Ferritic Steels

2007 ◽  
Author(s):  
Kazuo Yoshida ◽  
Hirotake Nakai ◽  
Minami Fukuda
Keyword(s):  
Creep Strength ◽  
Rupture Life ◽  
Ferritic Steels ◽  
Regulatory Review ◽  
Tensile Stresses ◽  
Life Evaluation ◽  
Term Creep ◽  
Region Splitting ◽  
Review Current

In order to evaluate long-term creep strength and to review current allowable tensile stresses of creep strength enhanced ferritic steels, a committee was organized in Japan Power Engineering and Inspection Corporation. In 2004FY and 2005FY, creep test data of Gr. 122, Gr. 91, Gr. 92, Gr. 23 and KA-SUS410J2TB steels were collected and analyzed by means of region splitting procedure in the committee. Based on the analysis, the allowable tensile stresses were reviewed in accordance with METI regulatory base. And the master curves for creep rupture life evaluation of welds were set forth furthermore based on the data analysis.

Cr concentration dependence of overestimation of long term creep life in strength enhanced high Cr ferritic steels

2010 ◽  
Vol 87 (6) ◽  
pp. 276-281 ◽  
Author(s):  
K. Maruyama ◽  
H. Ghassemi Armaki ◽  
R.P. Chen ◽  
K. Yoshimi ◽  
M. Yoshizawa ◽  
...  
Keyword(s):  
Concentration Dependence ◽  
Ferritic Steels ◽  
Creep Life ◽  
Cr Concentration ◽  
Term Creep
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