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Tadashi Furuhara - One of the best experts on this subject based on the ideXlab platform.
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three dimensional observations of morphology of low angle boundaries in ultra low carbon Lath Martensite
Journal of Electron Microscopy, 2017Co-Authors: Shigekazu Morito, Tadashi Furuhara, Takuya Ohba, Anh Hoang Pham, Taisuke Hayashi, Goro MiyamotoAbstract:: The Lath Martensite structure contains hierarchical substructures, such as blocks, packets and prior austenite grains. Generally, high-angle grain boundaries in the Lath Martensite structure, i.e. block boundaries, are correlated to mechanical properties. On the other hand, low-angle grain boundaries play an important role in morphological development. However, it is difficult to understand their nature because of the difficulty associated with the characterization of the complex morphologies by two-dimensional techniques. This study aims to identify the morphologies of low-angle boundaries in ultra-low carbon Lath Martensite. A serial-sectioning method and electron backscatter diffraction analysis are utilized to reconstruct three-dimensional objects and analyse their grain boundaries. A packet comprizes two low-angle grain boundaries - sub-block and fine packet boundaries. Sub-blocks exhibit porous morphology, with two large sub-blocks predominantly occupying a block. Several fine packets with different habit planes from the surrounding regions are observed. Fine packets are present in blocks, which frequently share a close-packed direction with the neighbouring fine packets. In addition, fine packets are in contact with the sub-block boundaries.
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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, Goro Miyamoto, Kohsaku Ushioda, 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, Goro Miyamoto, Kohsaku Ushioda, 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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continuous dynamic recrystallization during warm deformation of tempered Lath Martensite in a medium carbon steel
Key Engineering Materials, 2012Co-Authors: Naoya Kamikawa, Goro Miyamoto, Tadashi FuruharaAbstract:To Understand the Mechanisms of Accelerated Dynamic Recrystallization Behavior during the Warm Deformation of Martensites, the Tempered Lath Martensite of 0.4C Steel (Fe-0.399%C-1.96%Mn in Mass %) Was Deformed at 650 °C in Compression to Different Reductions, and Microstructural Evolution Was Investigated. During the Deformation, an Initial Lath Martensite Structure with a Complicated Morphology Was Gradually Changed into More Equiaxed Structure. After 50% Reduction and above, an Equiaxed, Fine Grained Structure Mainly Surrounded by High-Angle Boundaries Was Uniformly Formed with Dislocation Substructures, where the Dislocation Density in the Grains Is Relatively Low. Since there Was No Significant Boundary Migration during this Process, this Microstructural Evolution Can Be Termed as Continuous Dynamic Recrystallization.
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quantitative analysis of variant selection in ausformed Lath Martensite
Acta Materialia, 2012Co-Authors: Goro Miyamoto, Naoki Takayama, Naomichi Iwata, Tadashi FuruharaAbstract:Abstract Variant selection in Lath Martensite transformed from deformed austenite in a low-carbon low-alloy steel is examined quantitatively on the basis of electron backscatter diffraction analysis of Martensite, in concert with a novel method for the reconstruction of austenite orientation. At a strain of 10%, variants whose (0 1 1) α plane was nearly parallel to the primary slip plane in austenite ((1 1 1) γ ) were formed dominantly. At strains of 30% and 50%, variants whose (0 1 1) α plane was nearly parallel to the secondary slip plane ((−1 1 1) γ ) as well as the primary slip plane were formed. Transmission electron microscopy observation of an austenite-stabilized alloy deformed under the same condition as the low-carbon low-alloy steel clarified that microband structures develop along the primary and secondary slip planes of austenite when its orientation is close to the main component of the deformation texture in austenite. A simple variant selection model is proposed in which Martensite variants with habit planes nearly parallel to the primary and secondary slip planes nucleate preferentially on microband boundaries as a result of a smaller amount of activation energy and grow dominantly as a result of less inhibition from the microband boundaries.
Kazuki Takashima - One of the best experts on this subject based on the ideXlab platform.
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microstructure sensitive fatigue crack growth in Lath Martensite of low carbon steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2020Co-Authors: Shohei Ueki, Yoji Mine, Kazuki TakashimaAbstract:Abstract The elementary process of microstructural fatigue crack growth in single-packet structures with different habit-plane orientations to the loading axis was examined using miniature compact-tension specimens to comprehend the intrinsic resistance to fatigue crack growth in Lath Martensite of low carbon steel. When the angle between the loading axis and the normal to the habit plane (φ) was within ~45°, the cracks propagated nearly parallel to the habit plane. In packets with their habit planes nearly perpendicular (φ > ~70°) to the notch direction, the crack grew across the Laths because of damage accumulation through the activation of the out-of-plane slips, which increased the fatigue crack growth resistance. Post-fatigue-test electron microscopy revealed that the microstructural inhomogeneity of the low carbon steel enhanced the strain localisation in coarse Laths, which probably led to the premature fatigue crack growth. When the crack grew perpendicular to the habit plane, the intrinsic resistance to fatigue crack growth was higher in the fine-Lath region than in the coarse-Lath region.
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microstructural fatigue crack growth in single packet structures of ultra low carbon steel Lath Martensite
Scripta Materialia, 2019Co-Authors: Shohei Ueki, Shigekazu Morito, Yoji Mine, Takuya Matsumura, Kazuki TakashimaAbstract:Abstract Fatigue crack growth in single-packet structures with different habit-plane orientations was examined using miniature compact-tension specimens of ultra-low carbon steel to elucidate the elementary process of microstructural crack growth in Lath Martensite. The growth rates of fatigue cracks were higher in propagating along block boundaries than in running across blocks, while both cracks had a rippled fracture surface. Post-fatigue-test electron microscopy results suggest that the crack prefers to grow along the block boundaries with high slip symmetry rather than take a roundabout route through the cell boundaries formed owing to the interaction of activated dislocations with pre-existing dislocations inside blocks.
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anisotropy of strength and plasticity in Lath Martensite steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Kwangsik Kwak, Yoji Mine, Tsuyoshi Mayama, Kazuki TakashimaAbstract:Abstract Microtensile testing with a crystal plasticity analysis was employed using single block structured specimens to elucidate the anisotropic plasticity of Lath Martensite steel. Habit-plane-orientation-dependent yielding occurred in the single block specimens, as well as in the single packet specimens. This indicated that the plastic anisotropy arose from the substructure included in the block. The crystal plasticity analysis successfully reproduced the stress-strain behaviour of the single block and single packet structures by considering the dependency of the slip activity on the habit plane orientation. These calculations revealed that the restriction of the slip transfer at the block and sub-block boundaries slightly increased the flow stress, while the austenite retaining between the Martensite Laths might impact the slip activity, leading to the anisotropy of the strength and plasticity.
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micro tension behaviour of Lath Martensite structures of carbon steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Yoji Mine, Koichi Hirashita, Hiroki Takashima, Mitsuhiro Matsuda, Kazuki TakashimaAbstract:Abstract A micro-tension testing technique was used to investigate the deformation behaviour of Lath Martensite structures with several types of boundaries in carbon steel. The Martensite structures exhibited sufficient necking strains and ductile fractures, whereas the uniform strain was limited owing to a lack of strain-hardening ability despite the increased flow stress. The yield stress of the Lath Martensite structures strongly depended on the in-Lath-plane orientation. The critical resolved shear stress of the in-Lath-plane slip systems was considerably lower than that of the out-of-Lath-plane slip systems. This finding suggests that the block boundaries are an effective grain boundary for impeding dislocation gliding. Plastic deformation transfer was restricted by the packet boundaries, which greatly rotated the crystallographic orientation of the in-Lath-plane slip systems between neighbouring Martensite variants.
Shigekazu Morito - One of the best experts on this subject based on the ideXlab platform.
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Local distribution of orientation relationship and microstructure evolution of Lath Martensite in an ultra-low-carbon steel
Scripta Materialia, 2020Co-Authors: Taisuke Hayashi, Shigekazu Morito, Takuya OhbaAbstract:Abstract Local distribution of orientation relationship between austenite and Martensite is quantitatively examined using Lath Martensite in an ultra-low-carbon steel. Orientation relationship is systematically deviated between near Greninger–Troiano and Nishiyama–Wasserman orientation relationships around variant boundaries of the smallest misorientation pair, which is observed as the most frequent variant pair in the steel. Misorientation between this variant pair is decreased at some boundaries of the pair. Formation mechanism of the pair is discussed using the observed boundary characters.
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microstructural fatigue crack growth in single packet structures of ultra low carbon steel Lath Martensite
Scripta Materialia, 2019Co-Authors: Shohei Ueki, Shigekazu Morito, Yoji Mine, Takuya Matsumura, Kazuki TakashimaAbstract:Abstract Fatigue crack growth in single-packet structures with different habit-plane orientations was examined using miniature compact-tension specimens of ultra-low carbon steel to elucidate the elementary process of microstructural crack growth in Lath Martensite. The growth rates of fatigue cracks were higher in propagating along block boundaries than in running across blocks, while both cracks had a rippled fracture surface. Post-fatigue-test electron microscopy results suggest that the crack prefers to grow along the block boundaries with high slip symmetry rather than take a roundabout route through the cell boundaries formed owing to the interaction of activated dislocations with pre-existing dislocations inside blocks.
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three dimensional observations of morphology of low angle boundaries in ultra low carbon Lath Martensite
Journal of Electron Microscopy, 2017Co-Authors: Shigekazu Morito, Tadashi Furuhara, Takuya Ohba, Anh Hoang Pham, Taisuke Hayashi, Goro MiyamotoAbstract:: The Lath Martensite structure contains hierarchical substructures, such as blocks, packets and prior austenite grains. Generally, high-angle grain boundaries in the Lath Martensite structure, i.e. block boundaries, are correlated to mechanical properties. On the other hand, low-angle grain boundaries play an important role in morphological development. However, it is difficult to understand their nature because of the difficulty associated with the characterization of the complex morphologies by two-dimensional techniques. This study aims to identify the morphologies of low-angle boundaries in ultra-low carbon Lath Martensite. A serial-sectioning method and electron backscatter diffraction analysis are utilized to reconstruct three-dimensional objects and analyse their grain boundaries. A packet comprizes two low-angle grain boundaries - sub-block and fine packet boundaries. Sub-blocks exhibit porous morphology, with two large sub-blocks predominantly occupying a block. Several fine packets with different habit planes from the surrounding regions are observed. Fine packets are present in blocks, which frequently share a close-packed direction with the neighbouring fine packets. In addition, fine packets are in contact with the sub-block boundaries.
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energetic stability of boundary between variants in Lath Martensite
Journal of Alloys and Compounds, 2013Co-Authors: Anh Hoang Pham, Shigekazu Morito, Takuya Ohba, Taisuke HayashiAbstract:Abstract In this study we have evaluated the energetic stability of boundaries between Kurdjumov–Sachs (K–S) variants to explain the morphology of sub-block and block in Lath Martensite. Interfacial energy of different variant pairs was calculated by using molecular dynamics simulation. Three dimensional models of tilt and twist boundary with a method evaluating interfacial energy were developed. The results showed energetic stability of twist boundary with small misorientation from 0 to 5.5°/[0 1 1] α′ in consistence with previous transmission electron microscope observation. For other boundary with larger misorientation, the twin-related variants had the smallest interfacial energy although this variant pair was not frequently observed in electron backscatter diffraction analysis.
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evaluation of the block boundary and sub block boundary strengths of ferrous Lath Martensite using a micro bending test
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: Akinobu Shibata, Shigekazu Morito, Takashi Nagoshi, Masato Sone, Yakichi HigoAbstract:Abstract We report our investigation of the block boundary and sub-block boundary strengths of Lath Martensite evaluated through a micro-bending test. The sub-block boundaries contribute very little to the macroscopic strength of the Lath Martensite. In contrast, the presence of a block boundary in the specimen greatly increased the strength. In addition, the block boundary induced a serrated flow and load drop after yielding in the load–displacement curve. The load drop and serrated flow were attributable to dislocation pile-up and subsequent propagation of dislocations across the block boundary. In a microstructural observation of specimens after deformation, we found that a block boundary significantly restricts the motion of dislocations, while a sub-block boundary does not. We concluded that the block boundary is the most effective grain boundary for strength in Lath Martensite.
T. Maki - One of the best experts on this subject based on the ideXlab platform.
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formation of ultrafine grained ferrite by warm deformation of Lath Martensite in low alloy steels with different carbon content
Scripta Materialia, 2008Co-Authors: Behrang Poorganji, Goro Miyamoto, T. Maki, Tadashi FuruharaAbstract:Formation of ultrafine grained ferrite by warm deformation of tempered Lath Martensite was investigated in Fe–2Mn–(0.1–0.8)C (mass%) alloys. Analysis of initial microstructure shows that an increase in carbon content leads to a decrease of Lath Martensite block size. Fine equiaxed (α) grains surrounded by high-angle boundaries are formed by dynamic recrystallization. As carbon content increases, the recrystallized α grain size decreases. It is considered that dynamic recrystallization of tempered Lath Martensite is a continuous type.
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effect of block size on the strength of Lath Martensite in low carbon steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Shigekazu Morito, T. Maki, H Yoshida, Xiaoxu HuangAbstract:Abstract The microstructure and the strength of the Lath Martensite in Fe–0.2C and Fe–0.2C–2Mn alloys were analyzed as a function of the prior austenite grain size. The size of Martensite packets formed within individual austenite grains was controlled by the austenite grain size but not affected by the Mn addition. However, the further subdivision of packets into blocks differed significantly in the two alloys, and at a given austenite grain size a smaller block size was observed in the Mn containing alloy. The yield strength of the two alloys was related to the packet size and the block size, respectively, and the results suggested that the block size is the key structural parameter when analyzing the strength–structure relationship of Lath Martensite in low carbon steels.
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the morphology and crystallography of Lath Martensite in alloy steels
Acta Materialia, 2006Co-Authors: Shigekazu Morito, Tadashi Furuhara, T. Maki, Xiaoxu Huang, N HansenAbstract:The morphology and crystallography of Lath Martensite in two Mn-containing interstitial free steels and a maraging steel were examined in detail by a combination of transmission electron microscopy, electron backscatter diffraction in a scanning electron microscope and optical microscopy. Indirect determination of the orientation relationship between the Lath Martensite and the austenite was made by analysis of misorientation distributions, and a similar orientation relationship was found for the three alloys in accordance with previous observations in low-carbon steels. Furthermore, the formation of six variants in a given packet and the preferential arrangement into blocks of low-misorientation variant pairs demonstrate a universality of morphology and crystallography of Lath Martensite. The presence of six variants in a packet can be accounted for by the minimization of the total shape strain introduced during the transformation. The Lath boundaries developed within the volume of a certain variant show alternating misorientations and a mixed tilt and twist character characterizing these structures as low-energy dislocation structures.
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The morphology and crystallography of Lath Martensite in alloy steels
Acta Materialia, 2006Co-Authors: Shigekazu Morito, Xuedong Huang, Tadashi Furuhara, T. Maki, N HansenAbstract:The morphology and crystallography of Lath Martensite in two Mn-containing interstitial free steels and a maraging steel were examined in detail by a combination of transmission electron microscopy, electron backscatter diffraction in a scanning electron microscope and optical microscopy. Indirect determination of the orientation relationship between the Lath Martensite and the austenite was made by analysis of misorientation distributions, and a similar orientation relationship was found for the three alloys in accordance with previous observations in low-carbon steels. Furthermore, the formation of six variants in a given packet and the preferential arrangement into blocks of low-misorientation variant pairs demonstrate a universality of morphology and crystallography of Lath Martensite. The presence of six variants in a packet can be accounted for by the minimization of the total shape strain introduced during the transformation. The Lath boundaries developed within the volume of a certain variant show alternating misorientations and a mixed tilt and twist character characterizing these structures as low-energy dislocation structures. © 2006 Acta Materialia Inc.
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control of cementite precipitation in Lath Martensite by rapid heating and tempering
Isij International, 2004Co-Authors: Tadashi Furuhara, K Kobayashi, T. MakiAbstract:Lath Martensite structures, tempered at various temperatures (723-923 K) were studied by changing heating rates (2 K/s to 1 000 K/s) to the tempering temperature in an alloy steel for machine structural use (SCM435; Fe-0.35C-0.24Si-0.77Mn-1.05Cr-0.17Mo). Hardness of the rapidly heated (at 100 K/s or 1 000 K/s) specimen is larger than that of the slowly heated (at 2 K/s) specimen when tempering temperature and time are the same. Cementite precipitates are formed on high-angle boundaries (prior austenite grain boundary, block and packet boundaries) as well as within Laths and at low-angle boundaries (Lath boundaries) by tempering. TEM observation has revealed that finer cementite is dispersed more uniformly in the rapidly heated specimen than in the slowly heated specimen. It is considered that the temperature where cementite precipitation starts is raised by increasing the heating rate to tempering temperature, resulting in a higher nucleation rate and a finer dispersion of cementite.
Goro Miyamoto - One of the best experts on this subject based on the ideXlab platform.
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three dimensional observations of morphology of low angle boundaries in ultra low carbon Lath Martensite
Journal of Electron Microscopy, 2017Co-Authors: Shigekazu Morito, Tadashi Furuhara, Takuya Ohba, Anh Hoang Pham, Taisuke Hayashi, Goro MiyamotoAbstract:: The Lath Martensite structure contains hierarchical substructures, such as blocks, packets and prior austenite grains. Generally, high-angle grain boundaries in the Lath Martensite structure, i.e. block boundaries, are correlated to mechanical properties. On the other hand, low-angle grain boundaries play an important role in morphological development. However, it is difficult to understand their nature because of the difficulty associated with the characterization of the complex morphologies by two-dimensional techniques. This study aims to identify the morphologies of low-angle boundaries in ultra-low carbon Lath Martensite. A serial-sectioning method and electron backscatter diffraction analysis are utilized to reconstruct three-dimensional objects and analyse their grain boundaries. A packet comprizes two low-angle grain boundaries - sub-block and fine packet boundaries. Sub-blocks exhibit porous morphology, with two large sub-blocks predominantly occupying a block. Several fine packets with different habit planes from the surrounding regions are observed. Fine packets are present in blocks, which frequently share a close-packed direction with the neighbouring fine packets. In addition, fine packets are in contact with the sub-block boundaries.
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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, Goro Miyamoto, Kohsaku Ushioda, 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, Goro Miyamoto, Kohsaku Ushioda, 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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continuous dynamic recrystallization during warm deformation of tempered Lath Martensite in a medium carbon steel
Key Engineering Materials, 2012Co-Authors: Naoya Kamikawa, Goro Miyamoto, Tadashi FuruharaAbstract:To Understand the Mechanisms of Accelerated Dynamic Recrystallization Behavior during the Warm Deformation of Martensites, the Tempered Lath Martensite of 0.4C Steel (Fe-0.399%C-1.96%Mn in Mass %) Was Deformed at 650 °C in Compression to Different Reductions, and Microstructural Evolution Was Investigated. During the Deformation, an Initial Lath Martensite Structure with a Complicated Morphology Was Gradually Changed into More Equiaxed Structure. After 50% Reduction and above, an Equiaxed, Fine Grained Structure Mainly Surrounded by High-Angle Boundaries Was Uniformly Formed with Dislocation Substructures, where the Dislocation Density in the Grains Is Relatively Low. Since there Was No Significant Boundary Migration during this Process, this Microstructural Evolution Can Be Termed as Continuous Dynamic Recrystallization.
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quantitative analysis of variant selection in ausformed Lath Martensite
Acta Materialia, 2012Co-Authors: Goro Miyamoto, Naoki Takayama, Naomichi Iwata, Tadashi FuruharaAbstract:Abstract Variant selection in Lath Martensite transformed from deformed austenite in a low-carbon low-alloy steel is examined quantitatively on the basis of electron backscatter diffraction analysis of Martensite, in concert with a novel method for the reconstruction of austenite orientation. At a strain of 10%, variants whose (0 1 1) α plane was nearly parallel to the primary slip plane in austenite ((1 1 1) γ ) were formed dominantly. At strains of 30% and 50%, variants whose (0 1 1) α plane was nearly parallel to the secondary slip plane ((−1 1 1) γ ) as well as the primary slip plane were formed. Transmission electron microscopy observation of an austenite-stabilized alloy deformed under the same condition as the low-carbon low-alloy steel clarified that microband structures develop along the primary and secondary slip planes of austenite when its orientation is close to the main component of the deformation texture in austenite. A simple variant selection model is proposed in which Martensite variants with habit planes nearly parallel to the primary and secondary slip planes nucleate preferentially on microband boundaries as a result of a smaller amount of activation energy and grow dominantly as a result of less inhibition from the microband boundaries.
