The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Tadashi Furuhara - One of the best experts on this subject based on the ideXlab platform.
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Microstructure of reverted Austenite in Fe-0.3N martensite
Scripta Materialia, 2018Co-Authors: Mitsutaka Sato, Goro Miyamoto, Sou Matsumoto, Tadashi FuruharaAbstract:Abstract Reverse transformation behavior during intercritical annealing was studied in Fe-0.3 mass%N binary alloy. Two morphologies of acicular and globular Austenite are formed during reversion. The globular Austenite has almost same orientation with one side of adjacent prior Austenite grain and grows into the martensite with larger deviation angle from Kurdjumov-Sachs orientation relationship (K-S OR). On the other hand, the acicular Austenite holds a near K-S OR with its surrounding martensite matrix. A large amount of retained Austenite was obtained by a simple intercritical annealing due to enrichment of nitrogen into reverted Austenite.
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analysis of recrystallization behavior of hot deformed Austenite reconstructed from ebsd orientation maps of lath martensite
Materials Science Forum, 2016Co-Authors: Manabu Kubota, Kohsaku Ushioda, Goro Miyamoto, Tadashi FuruharaAbstract:The recrystallization behavior of hot-deformed Austenite of 0.55% C low alloy steels at 900, 850 and 800°C was investigated by a conventional double-hit compression test and a new method which reconstructs the parent Austenite orientation map from an EBSD (electron backscattering diffraction) orientation map of daughter lath martensite. The new method can clearly reconstruct the parent Austenite structure at high temperature from the daughter lath martensite structure and we can obtain the information on crystal orientation of the work-hardened Austenite. It was revealed that recrystallization of Austenite at 800 °C is significantly retarded by the addition of 0.1% V. The strong texture of parallel to the compression direction develops just after the hot-deformation, but this texture becomes weaker as the recrystallization progresses. By applying the reconstruction method, it becomes possible to evaluate various phenomena related to the hot-deformation of Austenite
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analysis of recrystallization behavior of hot deformed Austenite reconstructed from electron backscattering diffraction orientation maps of lath martensite
Scripta Materialia, 2016Co-Authors: Manabu Kubota, Kohsaku Ushioda, Goro Miyamoto, Tadashi FuruharaAbstract:Abstract The recrystallization behavior of hot-deformed Austenite of a 0.55% C steel at 800 °C was investigated by a method of reconstructing the parent Austenite orientation map from an electron backscattering diffraction orientation map of lath martensite. Recrystallized Austenite grains were clearly distinguished from un-recrystallized Austenite grains. Very good correlation was confirmed between the static recrystallization behavior investigated mechanically by double-hit compression tests and the change in Austenite microstructure evaluated by the reconstruction method. The recrystallization behavior of hot-deformed 0.55% C steel at 800 °C is directly revealed and it was observed that by addition of 0.1% V the recrystallization was significantly retarded.
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mapping the parent Austenite orientation reconstructed from the orientation of martensite by ebsd and its application to ausformed martensite
Acta Materialia, 2010Co-Authors: Goro Miyamoto, Naomichi Iwata, Naoki Takayama, Tadashi FuruharaAbstract:Abstract A new method is developed for reconstruction of the local orientation of the parent Austenite based on the orientation of lath martensite measured by electron backscattered diffraction. The local orientation of Austenite was obtained by least squares fitting as the difference between the experimental data and the predicted martensite orientation was minimal, assuming the specific orientation relationship (OR) between martensite and the parent Austenite. First, the average OR between Austenite and lath martensite was precisely determined and it was shown that both close packed planes and directions between martensite and the parent Austenite deviated by more than 1° in low carbon martensite. The quality of the reconstructed Austenite orientation map depended strongly on the OR used for the calculation. When Kurdjumov–Sachs (K–S) or Nishiyama–Wasserman (N–W) ORs were used the Austenite orientation was frequently mis-indexed as a twin orientation with respect to the true orientation because of the mirror symmetry of (0 1 1)α stacking in the K–S or N–W ORs. In contrast, the frequency of mis-indexing was significantly reduced by using the measured OR, where the close packed planes and directions were not parallel. The deformation structure in Austenite was successfully reconstructed by applying the proposed method to ausformed martensite in low carbon steel.
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precise measurement of strain accommodation in Austenite matrix surrounding martensite in ferrous alloys by electron backscatter diffraction analysis
Acta Materialia, 2009Co-Authors: Goro Miyamoto, T. Maki, Akinobu Shibata, Tadashi FuruharaAbstract:Local strain distributions in Austenite matrix that is deformed to accommodate shape strain associated with formation of martensite were investigated by means of electron backscatter diffraction (EBSD) analysis for various morphologies of lath, lenticular and thin plate martensite in ferrous alloys. By detecting small changes in EBSD patterns through image analysis of the patterns, components of both strain and rotation tensors in Austenite matrix adjacent to martensite were measured quantitatively. In the Austenite matrix surrounding thin plate martensite, the magnitude of components of strain tensor is nearly as large as those of rotation tensor, implying that shape strain of thin plate martensite is accommodated by elastic deformation of Austenite. On the other hand, in the Austenite matrices surrounding lenticular and lath martensite, components of strain tensor are found to be much smaller than those of rotation tensor even near the Austenite/martensite interface. This indicates that most of the shape strain associated with the formation of lenticular and lath martensite is accommodated by plastic deformation in the Austenite matrix. The misorientation axis of Austenite adjacent to lenticular and lath martensite coincides well with that predicted from the phenomenological theory of martensite crystallography.
A Charai - One of the best experts on this subject based on the ideXlab platform.
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effect of the bainitic transformation temperature on retained Austenite fraction and stability in ti microalloyed trip steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: A Kammouni, W Saikaly, Myriam Dumont, C Marteau, X Bano, A CharaiAbstract:TRIP properties in four hot-rolled microalloyed steels were studied as a function of bainitic domain entrance temperature. It was found that this temperature affects the size and morphology of the retained Austenite grains. Size and morphology was shown to play a role on the stability of the retained Austenite. This stability was shown to be the major factor affecting the mechanical properties of these steels. In the case of the lowest bainitic temperature, the TRIP effect is hindered due to the premature transformation of Austenite into martensite probably due to an insufficient carbon enrichment of the small Austenite grains. Moreover the bainitic treatment performed at the highest temperature contained a very low volume fraction of retained Austenite that does not transform even under deformation. Using TEM and the Kikuchi-line method, it was shown that the sample that did not undergo a phase transformation during FIB milling had a carbon concentration in its retained Austenite grains of approximately 1.7%.
A Kammouni - One of the best experts on this subject based on the ideXlab platform.
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effect of the bainitic transformation temperature on retained Austenite fraction and stability in ti microalloyed trip steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: A Kammouni, W Saikaly, Myriam Dumont, C Marteau, X Bano, A CharaiAbstract:TRIP properties in four hot-rolled microalloyed steels were studied as a function of bainitic domain entrance temperature. It was found that this temperature affects the size and morphology of the retained Austenite grains. Size and morphology was shown to play a role on the stability of the retained Austenite. This stability was shown to be the major factor affecting the mechanical properties of these steels. In the case of the lowest bainitic temperature, the TRIP effect is hindered due to the premature transformation of Austenite into martensite probably due to an insufficient carbon enrichment of the small Austenite grains. Moreover the bainitic treatment performed at the highest temperature contained a very low volume fraction of retained Austenite that does not transform even under deformation. Using TEM and the Kikuchi-line method, it was shown that the sample that did not undergo a phase transformation during FIB milling had a carbon concentration in its retained Austenite grains of approximately 1.7%.
H. K. D. H. Bhadeshia - One of the best experts on this subject based on the ideXlab platform.
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thermal stability of Austenite retained in bainitic steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: Saha A Podder, H. K. D. H. BhadeshiaAbstract:Abstract Steels with a microstructure consisting of a mixture of bainitic ferrite and carbon-enriched retained Austenite are of interest in a variety of commercial applications because they have been shown to exhibit good combinations of strength, toughness and ductility. However, their use at temperatures moderately above ambient requires a knowledge of the thermal stability of the Austenite. The changes that occur during the tempering of a mixture of bainitic ferrite, carbon-enriched retained Austenite and martensite have been characterised. An analysis of the volume change due to transformation shows that it is possible to distinguish the decomposition of Austenite from the tempering of martensite. The nature of the carbides that form during the heat treatment is discussed as are the implications on the development of mathematical models accounting for calculating the strain during Austenite decomposition and martensite tempering. It is found that the early stages of tempering reactions where the Austenite content is not greatly reduced, can dramatically influence the stability of the Austenite as it is cooled to ambient temperature.
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The reverse transformations in a high-strength high-hardenability Fe-C-Si-Mn-Mo steel
Journal of Materials Science, 1993Co-Authors: H. K. D. H. BhadeshiaAbstract:The kinetics of the reverse transformations from a mixture of bainitic ferrite and residual Austenite to Austenite have been investigated in a steel containing a relatively high silicon concentration. It was found that the reaustenitization process was initially rapid but slow at the end of reaction and the extent of Austenite formed increased with increasing reaustenitization temperature until all of the bainitic ferrite had been transformed to Austenite. The process of reaustenitization was followed by dilatometry, optical and transmission electron microscopy, and stereology. The results suggested that the formation of Austenite took place by the movement of planar ferrite/Austenite interfaces.
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Continuous heating transformation of bainite to Austenite
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1991Co-Authors: Jer-ren Yang, H. K. D. H. BhadeshiaAbstract:Abstract The transformation of a bainitic FeMnSiC alloy into Austenite has been studied using dilatometry, transmission electron microscopy and microanalytical techniques. The formation of Austenite was investigated using two different starting microstructures, the first consisting of a mixture of bainitic ferrite and residual Austenite, and the second of a mixture of tempered bainitic ferrite and carbides. Results from isothermal austenitization experiments confirm earlier work on a different alloy, that because of the incomplete reaction phenomenon associated with bainite growth, there is a large temperature hysteresis before the reverse transformation to Austenite becomes possible. Continuous heating experiments revealed an identical austenization behaviour for both initial microstructures when the heating rate utilized was small. This is because any residual Austenite then tends to transform into pearlite or to decompose into ferrite and discrete particles of carbides before the sample reaches a temperature where Austenite growth becomes thermodynamically feasible. Consequently, the two initial microstructures become identical by the time T γ is reached. At faster heating rates the residual Austenite remains stable during heating and then commences to grow as the appropriate elevated temperature is reached. A slightly higher degree of superheating is found to be necessary in the absence of residual Austenite in the starting microstructure, since Austenite nucleation is then necessary prior to growth. Since the excess superheating is rather small, the results indicate that nucleation does not appear to be a major hurdle to the formation of Austenite in the alloy studied.
Goro Miyamoto - One of the best experts on this subject based on the ideXlab platform.
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Microstructure of reverted Austenite in Fe-0.3N martensite
Scripta Materialia, 2018Co-Authors: Mitsutaka Sato, Goro Miyamoto, Sou Matsumoto, Tadashi FuruharaAbstract:Abstract Reverse transformation behavior during intercritical annealing was studied in Fe-0.3 mass%N binary alloy. Two morphologies of acicular and globular Austenite are formed during reversion. The globular Austenite has almost same orientation with one side of adjacent prior Austenite grain and grows into the martensite with larger deviation angle from Kurdjumov-Sachs orientation relationship (K-S OR). On the other hand, the acicular Austenite holds a near K-S OR with its surrounding martensite matrix. A large amount of retained Austenite was obtained by a simple intercritical annealing due to enrichment of nitrogen into reverted Austenite.
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analysis of recrystallization behavior of hot deformed Austenite reconstructed from ebsd orientation maps of lath martensite
Materials Science Forum, 2016Co-Authors: Manabu Kubota, Kohsaku Ushioda, Goro Miyamoto, Tadashi FuruharaAbstract:The recrystallization behavior of hot-deformed Austenite of 0.55% C low alloy steels at 900, 850 and 800°C was investigated by a conventional double-hit compression test and a new method which reconstructs the parent Austenite orientation map from an EBSD (electron backscattering diffraction) orientation map of daughter lath martensite. The new method can clearly reconstruct the parent Austenite structure at high temperature from the daughter lath martensite structure and we can obtain the information on crystal orientation of the work-hardened Austenite. It was revealed that recrystallization of Austenite at 800 °C is significantly retarded by the addition of 0.1% V. The strong texture of parallel to the compression direction develops just after the hot-deformation, but this texture becomes weaker as the recrystallization progresses. By applying the reconstruction method, it becomes possible to evaluate various phenomena related to the hot-deformation of Austenite
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analysis of recrystallization behavior of hot deformed Austenite reconstructed from electron backscattering diffraction orientation maps of lath martensite
Scripta Materialia, 2016Co-Authors: Manabu Kubota, Kohsaku Ushioda, Goro Miyamoto, Tadashi FuruharaAbstract:Abstract The recrystallization behavior of hot-deformed Austenite of a 0.55% C steel at 800 °C was investigated by a method of reconstructing the parent Austenite orientation map from an electron backscattering diffraction orientation map of lath martensite. Recrystallized Austenite grains were clearly distinguished from un-recrystallized Austenite grains. Very good correlation was confirmed between the static recrystallization behavior investigated mechanically by double-hit compression tests and the change in Austenite microstructure evaluated by the reconstruction method. The recrystallization behavior of hot-deformed 0.55% C steel at 800 °C is directly revealed and it was observed that by addition of 0.1% V the recrystallization was significantly retarded.
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mapping the parent Austenite orientation reconstructed from the orientation of martensite by ebsd and its application to ausformed martensite
Acta Materialia, 2010Co-Authors: Goro Miyamoto, Naomichi Iwata, Naoki Takayama, Tadashi FuruharaAbstract:Abstract A new method is developed for reconstruction of the local orientation of the parent Austenite based on the orientation of lath martensite measured by electron backscattered diffraction. The local orientation of Austenite was obtained by least squares fitting as the difference between the experimental data and the predicted martensite orientation was minimal, assuming the specific orientation relationship (OR) between martensite and the parent Austenite. First, the average OR between Austenite and lath martensite was precisely determined and it was shown that both close packed planes and directions between martensite and the parent Austenite deviated by more than 1° in low carbon martensite. The quality of the reconstructed Austenite orientation map depended strongly on the OR used for the calculation. When Kurdjumov–Sachs (K–S) or Nishiyama–Wasserman (N–W) ORs were used the Austenite orientation was frequently mis-indexed as a twin orientation with respect to the true orientation because of the mirror symmetry of (0 1 1)α stacking in the K–S or N–W ORs. In contrast, the frequency of mis-indexing was significantly reduced by using the measured OR, where the close packed planes and directions were not parallel. The deformation structure in Austenite was successfully reconstructed by applying the proposed method to ausformed martensite in low carbon steel.
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precise measurement of strain accommodation in Austenite matrix surrounding martensite in ferrous alloys by electron backscatter diffraction analysis
Acta Materialia, 2009Co-Authors: Goro Miyamoto, T. Maki, Akinobu Shibata, Tadashi FuruharaAbstract:Local strain distributions in Austenite matrix that is deformed to accommodate shape strain associated with formation of martensite were investigated by means of electron backscatter diffraction (EBSD) analysis for various morphologies of lath, lenticular and thin plate martensite in ferrous alloys. By detecting small changes in EBSD patterns through image analysis of the patterns, components of both strain and rotation tensors in Austenite matrix adjacent to martensite were measured quantitatively. In the Austenite matrix surrounding thin plate martensite, the magnitude of components of strain tensor is nearly as large as those of rotation tensor, implying that shape strain of thin plate martensite is accommodated by elastic deformation of Austenite. On the other hand, in the Austenite matrices surrounding lenticular and lath martensite, components of strain tensor are found to be much smaller than those of rotation tensor even near the Austenite/martensite interface. This indicates that most of the shape strain associated with the formation of lenticular and lath martensite is accommodated by plastic deformation in the Austenite matrix. The misorientation axis of Austenite adjacent to lenticular and lath martensite coincides well with that predicted from the phenomenological theory of martensite crystallography.
