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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575
Publisher: The Iron and Steel Institute of Japan

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Tetsu-to-Hagané Advance Publication

Influence of Crystal Structure and Chemical Composition on the Reducibility of Silico-Ferrite of Calcium and Aluminum in CO–CO2–H2–H2O Atmosphere

Daisuke Maruoka, Shojiro Mataoka, Eiki Kasai, Taichi Murakami

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Influence of Crystal Structure and Chemical Composition on the Reducibility of Silico-Ferrite of Calcium and Aluminum in CO–CO2–H2–H2O Atmosphere

Microstructural Analysis of Reduced Multicomponent Calcium Ferrite Using STEM-EDS and 3DAP

Kohei Ikeda, Michitoshi Saeki, Kenta Takehara, Masanari Tomozawa, Takashi Kawano

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Microstructural Analysis of Reduced Multicomponent Calcium Ferrite Using STEM-EDS and 3DAP

Effect of Iron Ore Properties on Melting and Assimilation Phenomena in Parallel Granulation with Inclined Mixing of Limestone

Shintaro Yamazaki, Takero Adachi, Hiroyuki Taguchi, Koji Osuga, Kisato Koga, Masahiro Yakeya, Kazuya Miyagawa

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Effect of Iron Ore Properties on Melting and Assimilation Phenomena in Parallel Granulation with Inclined Mixing of Limestone

Effects of Re-ignition and Coke Breeze Reduction on Sinter Microstructure in Sintering Process

Keisuke Hirano, Kazumasa Tsutsui, Toru Takayama, Masaru Matsumura

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Effects of Re-ignition and Coke Breeze Reduction on Sinter Microstructure in Sintering Process

Effect of Mineral Phase Ratios on Reduction Behavior of Multi-component Calcium Ferrite Extracted from Iron Ore Sinter

Daisuke Maruoka, Nanase Kimura, Eiki Kasai, Taichi Murakami

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Effect of Mineral Phase Ratios on Reduction Behavior of Multi-component Calcium Ferrite Extracted from Iron Ore Sinter

Analysis of Peritectic Solidification of Ag–Sn Alloys by Unidirectional Solidification Experiment

Takaya Horino, Hiroshi Harada

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Analysis of Peritectic Solidification of Ag–Sn Alloys by Unidirectional Solidification Experiment

Effect of Fe2+/Fe3+ Ratio on the Reduction Behavior of SFCA-I in Hydrogen-enriched Atmosphere

Daisuke Maruoka, Yuto Onuma, Eiki Kasai, Taichi Murakami

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Effect of Fe2+/Fe3+ Ratio on the Reduction Behavior of SFCA-I in Hydrogen-enriched Atmosphere

Effect of Decreasing Gas Flow Rate between Two Ignition Furnaces on Sinter Yield at REMO-tec (Re-ignition sintering) Process

Masaru Matsumura, Keigo Noda, Kohei Okada, Junji Nagata, Kenichi Higuchi

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Effect of Decreasing Gas Flow Rate between Two Ignition Furnaces on Sinter Yield at REMO-tec (Re-ignition sintering) Process

Process for Phosphorus Recovery from Phosphorus-concentrated Steelmaking Slag and Decreasing Slag Volume

Takayuki Iwama, Ryo Inoue, Kenji Nakase, Katsunori Yamaguchi, Shigeru Ueda

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Process for Phosphorus Recovery from Phosphorus-concentrated Steelmaking Slag and Decreasing Slag Volume

Yield Prediction Based on Bed Temperature and Component in Sintering Process

Yuji Iwami, Kenya Horita, Tetsuya Yamamoto, Noritaka Saito, Kunihiko Nakashima

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Yield Prediction Based on Bed Temperature and Component in Sintering Process

Hydrogen Embrittlement Susceptibility of Linear Friction Welded Medium Carbon Steel Joints

Riki Toramoto, Takayuki Yamashita, Kohsaku Ushioda, Tomohiko Omura, Hidetoshi Fujii

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Hydrogen Embrittlement Susceptibility of Linear Friction Welded Medium Carbon Steel Joints

Mechanical Properties and Fracture Characteristics in High Mn Austenitic Steel for Cryogenic Applications

Daichi Izumi, Keiji Ueda, Hiroto Shoji, Mitsuru Ohata, Tetsuya Tagawa

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Mechanical Properties and Fracture Characteristics in High Mn Austenitic Steel for Cryogenic Applications

Crater End Detection in Continuous Casting by Longitudinal and Shear Wave Hybrid Technique with High Sensitivity EMAT

Yuji Nishizawa, Keigo Toishi, Tomohiro Tanaka, Yukinori Iizuka

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Crater End Detection in Continuous Casting by Longitudinal and Shear Wave Hybrid Technique with High Sensitivity EMAT

Federated Learning of Creep Rupture Time and High Temperature Tensile Strength Prediction Models

Junya Sakurai, Keisuke Torigata, Manabu Matsunaga, Naoto Takanashi, Shinya Hibino, Kenichi Kizu, Akira Morita, Masahiro Inomoto, Nobuaki Shimohata, Kodai Toyota, Tadaaki Nakamura, Keita Hashimoto, Tatsuya Okubo, Loic Beheshti, Vincent Richard, Masahiko Demura

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Federated Learning of Creep Rupture Time and High Temperature Tensile Strength Prediction Models

Surface Cracking in Hot Rolling Process of Cu Bearing Steel Bar

Naoki Tsuchida, Koharu Nishio, Ryo Matsumoto, Hiroshi Utsunomiya, Naoki Maruyama, Kosuke Hayashi, Yasuyoshi Hidaka, Hiroshi Tanei

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Surface Cracking in Hot Rolling Process of Cu Bearing Steel Bar

Micromechanism of Heterogeneous Reduction of Iron Ore Sinters Investigated by Synchrotron X-Ray Multimodal Analysis

Yasuo Takeichi, Reiko Murao, Masao Kimura

Abstract

The reducibility and mechanical properties of iron ore sinter in blast furnace is critical to effective plant operation. The reduction reaction of sinters progresses heterogeneously owing to microstructures with various mineral phases and pore networks. The reduction process was investigated by semi-microbeam synchrotron X-ray multimodal analysis. Heterogeneous chemical state evolution of Fe and trigger sites of crack formation were visualized using two-dimensional Fe K-edge X-ray absorption near-edge structure analysis and were discussed based on reduction gas transfer. The elemental composition map and X-ray diffraction microanalysis were also combined to reveal the microprocesses during the reduction, such as calcium ferrite decomposition and crystal grain growth.

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Micromechanism of Heterogeneous Reduction of Iron Ore Sinters Investigated by Synchrotron X-Ray Multimodal Analysis

Effect of Solidification Structure Morphology on Macrosegregation Generated by Solidification Shrinkage Flow Due to Bridging

Muneto Sasaki, Yukinobu Natsume

Abstract

Casting experiments of Al-10 wt.%Cu alloy were carried out using an impreved Satou mold (iST mold). The mold was a rectangular parallelepiped (inner dimensions 30 mmT × 50 mmW × 140 mmH), with a porous alumina plate on the wide side of the mold and a chill set at a height of 70 to 80 mm from the bottom. Four metal materials (stainless, steel, brass, and copper) with different thermal conductivities were used for the chill. To investigate the effect of bridging on the formation of macrosegregation, X-ray CT analysis of the macrosegregation distribution and morphology, observation of micro- and macro-structures, and analysis of temperature and solid fraction distribution were performed for samples obtained under each condition. Bridging formed near the chill under all conditions, and channels consisting of positive segregation and cavities were formed below it. The volume fraction of positive segregation decreased as the thermal conductivity of the chill material increased. In the samples using stainless and copper as chill materials, the volume fractions of positive segregation were 73.8 % and 11.7 %, respectively. Consequently, we confirmed that the bridging-formed conditions have a significant effect on the formation of macrosegregation.

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Effect of Solidification Structure Morphology on Macrosegregation Generated by Solidification Shrinkage Flow Due to Bridging

Crack Formation Process in Galvanized Steel Under Dwell Fatigue

Kayo Hasegawa, Shatumbu Thomas Alweedo, Motoaki Morita

Abstract

The study investigated the dwell fatigue characteristics of hot-dip galvanized steel. Cyclic and dwell fatigue tests were conducted, their fatigue life was compared, and fracture surfaces were analyzed. When the cyclic maximum stress (σmax) was the upper yield stress (σUYS), there was hardly a difference in fatigue life between cyclic and dwell fatigues. In σmax=0.9 × σUYS, the fatigue life in dwell fatigue was shorter than that in cyclic fatigue. The cracks under dwell fatigue were generated in σmax= σUYS before N=10 cycles. Their cracks did not grow until N=100,000 cycles. On the other hand, no cracks were observed on the specimen surface under cyclic fatigue before N=100,000 cycles. The formation of cracks on the surface of the galvanized layer under cyclic dwell was remarkably delayed compared to that under dwell fatigue, regardless of the applied stresses in this study. Therefore, dwell fatigue mode debases the surface of the hot-dip galvanized steel. The applied stress affected the crack morphology on the specimen surface. In σmax= σUYS, the large cracks were observed at the grain boundary triple junctions. In σmax=0.9 × σUYS, not only the cracks at triple junctions of grain boundary but also some cavities along the grain boundaries were detected. Their defects were often reported under creep deformation. The cavities seemed to adjoin each other and coalesce. In the stress relaxation testing, the hot-dip galvanized steel exhibited creep behavior. The decrease in the fatigue life under dwell fatigue would be due to the creep phenomena.

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Crack Formation Process in Galvanized Steel Under Dwell Fatigue

Microstructural Analysis of Slip Mechanisms in Friction-type Joints Using Ascoated Hot-dip Galvanized Steel and High-strength Bolts

Norihiko L. Okamoto, Hayato Kobayashi, Tetsu Ichitsubo

Abstract

The friction-type joints using high-strength bolts are frequently employed for the assembly of structural steel components. The drawback of the combination of the friction-type joints and hot-dip galvanized steel plates for highly corrosive environments is the low slip coefficient at the friction interface in the as-coated condition. To increase the slip coefficient, labor-intensive blast processing or phosphate treatment is applied to the surface of the galvanized steel plates before assembly. In this study, we investigated the slip mechanism at the friction interface between as-galvanized steel plates through slip resistance tests on high-strength bolted friction joints, in hope of determining effective methods for overcoming the low slip coefficient in the as-coated condition. In the as-galvanized material, both the outermost Zn- and ζ(FeZn13)-phase layers exhibit c-axis texture. Since the easiest basal (dislocation) slip plane for the Zn phase with the hexagonal close-packed structure is parallel to the friction interface, the Zn phase is geometrically prone to plastic deformation due to the shear stress applied on the friction interface. The evidence that the coarse-grained Zn phase was refined to small crystal grains upon macroscopic slippage at the friction interface indicated that the low slip coefficient was attributed to the readily deformable nature of the outmost Zn phase. Potential strategies for increasing the slip coefficient without pre-surface treatment include strengthening the soft Zn phase through grain refinement or texture modification, or complete removal of the Zn phase during galvanizing.

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Microstructural Analysis of Slip Mechanisms in Friction-type Joints Using Ascoated Hot-dip Galvanized Steel and High-strength Bolts

Viscosity Measurement of Foam with High Gas Volume Fraction Using Sphere Pull-up and Dam-break Experiments

Shinya Sugi, Yoshihiko Higuchi

Abstract

Viscosity measurements of a gas-liquid two-phase fluid (foam) with fine bubbles were conducted using a sphere pull-up method and the flow behavior in dam-break experiments was evaluated. The following results were obtained.

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Viscosity Measurement of Foam with High Gas Volume Fraction Using Sphere Pull-up and Dam-break Experiments

Phase-field Simulation of the Stability of Fe2Al5 Phase at Fe/molten Zn–Al interface

Shunsuke Shiotani, Yuhki Tsukada, Toshiyuki Koyama

Abstract

The stability of η-Fe2Al5 phase at α-Fe/molten Zn–0.1Al (wt.%) (L) interface at 723 K in Fe–Zn–Al ternary system was investigated by phase-field simulations. Thin layers of intermetallic compound (IMC) phases (η,Г-Fe3Zn10,Г1-Fe5Zn21 and δ1-FeZn7) were placed between the α and L phases, and the growth of the IMC layers and the atomic diffusion of constituent elements along the direction perpendicular to the α/L interface were calculated by one-dimensional phase-field simulation. The simulation result showed that Г and Г1 phases dissolved, and thin η phase and thick δ1 phase remained stable at the α/L interface. Moreover, several phase-field simulations were performed by varying the values of interdiffusion coefficients in each phase. The simulation results showed that the diffusion and partitioning behaviors of Al have a significant effect on the stability of IMC layers at the α/L interface. It was found that the partitioning of Al to the α phase was suppressed due to the fact that the value of interdiffusion coefficient in the α phase was several orders of magnitude smaller than those in the IMC phases. The resultant Al partitioning to the IMC phases was the direct cause of the stabilization of the η phase and the destabilization of the Г and Г1 phases.

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Phase-field Simulation of the Stability of Fe2Al5 Phase at Fe/molten Zn–Al interface

Corrosion Resistance of Ni-coated Steel Sheets in Lithium-ion Battery Electrolyte

Misaki Masatsugu, Shintaro Yamanaka, Takehiro Takahashi, Kiyokazu Ishizuka

Abstract

In order to improve both performance and safety of lithium-ion batteries, we investigated the use of steel sheets which have a higher melting point than aluminum currently used for cell cases of lithium-ion batteries, for cell cases. First, a coating metal that can suppress Fe dissolution was selected, because corrosion resistance to battery electrolyte is important for battery cell cases. We found that Ni has high corrosion resistance to battery electrolyte, and that Ni-coated steel sheets can reduce the risk of short circuits due to decrease in Fe dissolution and re-deposition compared to non-coated steel sheets.

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Corrosion Resistance of Ni-coated Steel Sheets in Lithium-ion Battery Electrolyte

Effects of Interface Anisotropy on the Solidification Morphology of Zinc Alloys and Development of Data Assimilation for Their Estimation

Ayano Yamamura, Hideyuki Yasuda, Tomohiro Takaki

Abstract

The solid–liquid interface energy anisotropy of Zn alloys remains poorly understood. Recently, characteristic 14-arm dendritic growth has been observed using time-resolved X-ray computed tomography at SPring-8 during the solidification of a Zn-4mass%Al alloy. This study investigates the dependence of the dendrite morphologies of Zn alloys on solid–liquid interface energy anisotropy through systematic phase-field simulations of the growth of an isolated equiaxed dendrite. We also develop a data assimilation system to estimate the anisotropy parameters of solid–liquid interface energy and crystal orientation in Zn alloys and validate the system through twin experiments. This study provides insights into the solidification of Zn alloys and a powerful tool for their investigation.

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Effects of Interface Anisotropy on the Solidification Morphology of Zinc Alloys and Development of Data Assimilation for Their Estimation

Friction Stir Welding of Fe-15Mn-10Cr-8Ni-4Si Seismic Damping Alloy

Tomoya Nagira, Terumi Nakamura, Takahiro Sawaguchi, Masakazu Mori, Yoshiaki Morisada, Hidetoshi Fujii

Abstract

Friction stir welding (FSW) was applied to a 10 mm-thick plate for the Fe-15Mn-10Cr-8Ni-4Si seismic damping alloy. A sound FSW joint was obtained successfully without macro-defects such as groove-like defects and tunnel holes. However, small pores with diameters of 1–5 μm were formed owing to the wear of the FSW tool during the FSW. The decrease in the heat input suppressed the tool wear. Consequently, the distribution of small pores was limited to the border of the stir zone at the advancing side under smaller heat input conditions. The stir zone of the FSW specimen produced at 125 rpm showed a higher tensile strength of 759 MPa owing to the grain refinement and the high elongation of 50% compared with the base metal. In addition, the stir zone exhibited a remarkable fatigue life of 9,723 cycles. This was higher than that of the base metal (8,908 cycles). Grain refinement occurred by discontinuous dynamic recrystallization (DDRX) via high-angle boundary bulging and direct nucleation in the high-dislocation area. The increase in the heat input suppressed the DDRX owing to the promotion of dynamic recovery.

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Friction Stir Welding of Fe-15Mn-10Cr-8Ni-4Si Seismic Damping Alloy

Effect of B on Surface Oxidation Behavior and Phosphatability of Si-Mn-added Cold-Rolled Steel Sheets

Shinichi Furuya, Tadachika Chiba, Daisuke Mizuno

Abstract

The effect of B on the surface oxidation behavior and phosphatability of cold-rolled steel sheets was investigated using 0.001 wt% B-added and B-free steels containing 0.6 wt% Si and 2.0 wt% Mn. The specimens were annealed at 800 ℃ in a 5 vol% H2-N2 atmosphere with a dew point of -50 ℃. The surface oxides of the annealed samples were analyzed by GD-OES, FT-IR, SEM-EDX and TEM. The annealed steel sheets were then subjected to zinc phosphate treatment, and the effect of the surface oxides on phosphatability was evaluated by SEM-EDX. In the initial stage of annealing, fine granular Mn2SiO4 mainly formed and film-like SiO2 partly formed on both steels. As the soaking time at 800 °C increased, the granular Mn2SiO4 increased in the B-free steel. In contrast, in the B-added steel, the granular Mn2SiO4 coarsened, MnSiO3, MnO and B2O3 formed, and the film-like SiO2 formation area expanded. Addition of B reduced the melting point, causing coarsening of Mn2SiO4, exposing the base steel. This results in a difference in the oxygen potential between the exposed area of the steel and the oxide covered area. This local inhomogeneity of the oxygen potential changes the surface oxide species of the B-added steel. To elucidate the reason for the poor phosphatability of the B-added steel, a SEM-EDS analysis of the steel surface in the initial stage of zinc phosphate treatment was conducted, revealing that the coarse Si-Mn complex oxides and large film-like SiO2 inhibited the zinc phosphate reaction.

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Effect of B on Surface Oxidation Behavior and Phosphatability of Si-Mn-added Cold-Rolled Steel Sheets

Microstructure Development during Creep Deformation of 9Cr-1Mo-V-Nb Steel with Excess Nitrogen Introduced by Solution Nitriding – Multidimensional Scatter Diagram Analysis of STEM-EDS Maps by Machine Learning –

Tomotaka Hatakeyama, Shuntaro Ida, Kota Sawada, Kyosuke Yoshimi

Abstract

Creep deformation and precipitation behavior of 9Cr-1Mo-V-Nb steel with excess nitrogen introduced by solution nitriding were investigated. Precipitation of Cr2N phase was confirmed in addition to M23C6 and MX phases in the tempered microstructure. The creep strength of the steel was significantly reduced by solution nitriding, while the creep rupture elongation was increased. To characterize the complex precipitation behavior of the nitrogen-added steel, a machine learning-based clustering method of the multidimensional scatter diagram of the X-ray intensity of the alloying elements in each pixel of a STEM-EDS map was developed. Reduced number density of precipitates and enhanced coarsening kinetics of both Cr2N and MX were proposed as the mechanism of weakening caused by excess nitrogen.

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Microstructure Development during Creep Deformation of 9Cr-1Mo-V-Nb Steel with Excess Nitrogen Introduced by Solution Nitriding – Multidimensional Scatter Diagram Analysis of STEM-EDS Maps by Machine Learning –

Role of Si Addition in Interfacial Reactions of Steel Sheets Hot-dipped in Zn-55%Al Alloy Melt

Yasuo Omi, Dasom KIM, Naoki Takata, Asuka Suzuki, Makoto Kobashi, Suzue Yoneda

Abstract

This study was set to fundamentally understand the effect of Si addition on the interfacial reaction between Zn-55%Al alloy liquid (corresponding to a nominal composition of Al-25Zn (at%)) and Fe solid in the production process of GALVALUME steel sheets. The pure Fe sheets were hot-dipped in Al-25Zn and Al-25Zn-2Si (at%) alloy melts at 600, 650, and 700oC for 2~3600 s. Significantly thick coatings were formed on Fe sheets hot-dipped in the Al-25Zn binary alloy melt for a longer time than 10 s. The coating thickness became several millimeters after 30 s, resulting in a delamination of the coating. The significant Fe dissolution occurred in the Al-Zn binary alloy melt, accompanied by a significant growth of η phase (Fe2Al5) toward the solid Fe. The growth could be promoted by the Zn-rich liquid phase with a lower melting temperature. However, in the case of hot-dipping in the Al-25Zn-2Si ternary alloy melt, uniform coatings were formed on the hot-dipped Fe sheets due to the suppressed interfacial reactions. The Fe dissolution slightly occurred, and a continuous layer of Si-rich T5 (Fe2Al7.4Si) phase was formed at the interface of solid Fe with the Al-25Zn-2Si alloy melt. The continuous T5 phase layer would play a role in a diffusion barrier at the interface of solid Fe with liquid Al-Zn alloy, resulting in the suppressed interfacial reaction. These interfacial reaction processes are discussed based on thermodynamic calculations of the Fe-Al-Zn ternary and Fe-Al-Zn-Si quaternary systems.

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Role of Si Addition in Interfacial Reactions of Steel Sheets Hot-dipped in Zn-55%Al Alloy Melt

Formation Behavior of Fe–Zn Intermetallic Layers at the Interface between Fe–Mn and Pure Zn Melt at 460°C

Suzue Yoneda, Naoki Takata

Abstract

The effect of Mn on the alloying reaction during hot-dip galvanization was investigated. The microstructure of the Fe–Zn intermetallic layers consisted of ζ, δ, and Γ phases for both pure Fe and Fe–2Mn (wt.%) alloy. The intermetallic layers grew thicker with increasing dipping time, and the growth rate of each layer was similar for both substrates. In the case of Fe–2Mn, the formation of the δ1p phase was observed after dipping for 2 s. However, δ1p formation was delayed for pure Fe, indicating that Mn may promote nucleation of the δ1p phase. It is known that the δ1p phase nucleates in the Fe-saturated ζ phase. The Fe content at the ζ/δ1p interface was found to be lower for the Fe–2Mn alloy by electron probe microanalysis, suggesting that the supersaturation of Fe for the nucleation of δ1p is decreased by Mn addition and Mn may stabilize the δ1p phase. Once δ1p became a continuous layer, the growth rates of the δ1p layer on pure Fe and Fe–2Mn were similar. Mn could affect only the nucleation of δ1p during the initial stage of the alloying reaction.

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Formation Behavior of Fe–Zn Intermetallic Layers at the Interface between Fe–Mn and Pure Zn Melt at 460°C

Change in Dislocation Density via Ausforming in Fe-5%Mn-C Alloy with Lath Martensitic Structure

Misa Takanashi, Ryota Hidaka, Kota Ohkubo, Takuro Masumura, Toshihiro Tsuchiyama, Satoshi Morooka, Takuya Maeda, Shuichi Nakamura, Ryuji Uemori

Abstract

The strengthening mechanism of ausforming in martensitic steels is believed to be due to the inheritance of dislocations in austenite by the subsequently transformed martensite. However, no studies to date have quantified the dislocation density before and after ausforming. In this study, the dislocation densities of Fe-5%Mn-C alloys were analyzed, and the relationship between hardening by ausforming and dislocation accumulation, as well as the effect of carbon on this relationship, were investigated. The hardness of ausformed martensite increased with the ausforming reduction in austenite, and the strengthening effect of ausforming increased with the addition of carbon. Similarly, the dislocation density of ausformed martensite increased with the ausforming reduction in austenite, and the dislocation accumulation by ausforming increased with the addition of carbon. Because the hardness of the ausformed martensite follows the Bailey–Hirsch relationship, the strengthening mechanism owing to ausforming could be explained by dislocation strengthening. To understand the dislocation accumulation process during ausforming, the dislocation density of austenite immediately after ausforming was measured by in-situ heating neutron diffraction. Consequently, the dislocation density of the ausformed austenite was not dependent on the carbon content, indicating that dislocations are not inherited in carbon-free steels. By contrast, in steels with sufficient carbon content, not only are dislocations inherited but additional dislocations are introduced during martensitic transformation.

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Change in Dislocation Density via Ausforming in Fe-5%Mn-C Alloy with Lath Martensitic Structure

Direct Observation of Atomic Arrangement in Multicomponent Calcium Ferrite Using Scanning Transmission Electron Microscopy

Kenta Takehara, Kohei Ikeda, Takashi Kawano, Takahide Higuchi

Abstract

To reduce the reducing agent ratio and CO2 emissions in blast furnace operation, it is important to control the material structure of sintered ore, which affects its metallurgical and mechanical properties. Multicomponent calcium ferrites (also called CF or SFCA (silico-ferrite of calcium and aluminum)), which is a type of melting and solidification structure, has attracted considerable interest recently, and the chemical composition and crystal structure of each CF have been researched. Although the crystal structure of CF has conventionally been analyzed mainly by XRD, the atomic arrangement could not be observed directly. Therefore, in this study, CF was investigated at the atomic level by scanning transmission electron microscopy (STEM). This research revealed that acicular CF, which was previously understood to be SFCA-I, has a SFCA (≠ SFCA-I)structure. It was also found that columnar CF had a non-periodic SFCA structure induced with a magnetite-like structure. Furthermore, a CF in which SFCA and SFCA-I were alternately stacked repeatedly was also discovered. This research clarified the fact that CF has a non-periodic structure at the atomic level.

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Direct Observation of Atomic Arrangement in Multicomponent Calcium Ferrite Using Scanning Transmission Electron Microscopy

Effect of Alumina on the Phase Equilibria of the Iron-rich Corner of the CaO-SiO2-Fe2O3 System at 1240°C in Air

Amane Takahashi, Yukihiro Uchisawa, Hirokazu Sato, Takashi Watanabe, Rie Endo, Masahiro Susa, Miyuki Hayashi

Abstract

The effect of Al2O3 on the compositional region of silico-ferrite of calcium and aluminum (SFCA) and the liquid phase and the phase equilibria, including SFCA, was investigated in a CaO-SiO2-Fe2O3-5mass%Al2O3 system at 1240 °C in air. To obtain the desired composition, reagent-grade CaCO3, SiO2, Fe2O3, and Al2O3 powders were weighed, mixed, and equilibrated at 1240 °C in air. Each obtained sample was divided into two parts: one was pulverized into a powder and analyzed by XRD, and the other was subjected to microstructural observation and compositional analysis using EPMA. The results revealed that the compositional region of SFCA lies on the CF3-CA3-C4S3 plane and is C/S = 2.77–7.60 for 5 mass% Al2O3. Compared with the SFC composition region for 0 mass% Al2O3, the compositional range of SFCA extended in the CF3-C4S3 direction, suggesting that the addition of Al2O3 contributes to the stability of SFCA. Furthermore, the liquid-phase region was divided into a ferrite melt with a high Fe2O3 concentration and a silicate melt with a high SiO2 concentration, both of which shifted to the lower Fe2O3 side compared to the liquidus isotherm in the CaO-SiO2-Fe2O3 system. Unlike CaO-SiO2-Fe2O3, SFCA-I (SFC-I) was observed in the CaO-SiO2-Fe2O3-5mass%Al2O3 system, thus indicating that the addition of Al2O3 contributes to the stability of SFCA-I.

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Effect of Alumina on the Phase Equilibria of the Iron-rich Corner of the CaO-SiO2-Fe2O3 System at 1240°C in Air

Equation of Cleavege Fracture and Grain Boundary Fracture Stress Based on Brechet-Louchet Model

Katsutoshi Hyodo, Yosuke Nonaka, Kazuma Itoh, Tetsuya Namegawa

Abstract

New fracture process model of cleavage fracture initiated from cementite crack was proposed. In addition, the equation of propagation of cementite crack into the ferrite grain was developed based on the Brechet-Louchet model. This equation can reproduce not only ferrite size dependence of cleavage fracture stress that the Petch model can reproduce but both of test temperature dependence and strain rate dependence of fracture stress. Furthermore, in exchanging surface energy for grain boundary cohesive energy in the equation, grain boundary fracture stress can be also estimated.

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Equation of Cleavege Fracture and Grain Boundary Fracture Stress Based on Brechet-Louchet Model

Phase Stability and Thermal Expansion Properties of Additive Manufactured Super Invar alloy

Senlin Cai, Ryota Nagashima, Yaw Wang Chai, Naoki Sakaguchi, Nobuo Nakada

Abstract

Super invar alloy, Fe–32%Ni–5%Co, is widely utilized in precision instruments due to its remarkably low thermal expansion coefficient. Additive manufacturing holds promise for fabricating complex-shaped components with this alloy. This study investigated the phase stability and thermal expansion properties of super invar alloy fabricated via Laser Powder Bed Fusion (AM sample), comparing them to those of conventionally cast material (Re-melt sample). Microstructural analysis indicates that the AM sample has a more stable austenitic structure, attributed to minimal micro-segregation. Furthermore, it was observed that the thermal expansion coefficient decreases consistently with higher cooling rates within the temperature range of 400-300 K. As a result, AM sample exhibits lower expansion coefficient and it maintains at lower temperatures.

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Phase Stability and Thermal Expansion Properties of Additive Manufactured Super Invar alloy

Effect of BN Surface Segregation on Coatability in Hot-dip Galvanizing of B-added Steel

Daisuke Tahara, Katsuya Hoshino, Shoichiro Taira

Abstract

Boron (B) is frequently used as additives to improve the hardenability of advanced high strength steel. It has been reported that B in steel reacts with atmospheric N2 during annealing at low oxygen potential (low dew point) to form boron nitride (BN) by the thermodynamical calculation. In this study, the effect of BN formation on the steel surface on the coatability during hot-dip galvanizing was investigated, experimentally. B-free specimens and specimens containing 15 or 30 ppm B were annealed at various temperature and dew point, and then hot-dip galvanized. The annealed specimens were also prepared and analyzed with GD-OES, XPS, SEM-EDX and TEM-EELS to investigate the oxide and nitride formation on the steel surface during annealing. As results, coatability deteriorated as the amount of B in steel and the annealing temperature increase, and as the dew point decrease. These trends were not correlated with the amount of oxide but the amount of BN formation, suggesting that BN formation deteriorated the coatability. The surface and cross-sectional analysis revealed that BN formed around the oxide to cover the steel surface. This would lead the deterioration of the coatability because most of the steel surface was covered with BN as well as oxide, which are known to have low wettability with molten Zn.

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Effect of BN Surface Segregation on Coatability in Hot-dip Galvanizing of B-added Steel

Effect of Re-ignition Method on Sinter Yield Through Improving Carbon Combustion Ratio at Upper Layer of Sinter Packed Bed

Masaru Matsumura, Ryota Kosugi, Yuichiro Yamamoto, Junji Nagata, Kenichi Higuchi

Abstract

Conventionally, it has been known that the product yield of the upper part of the sintering layer is extremely low, because of the heat loss caused by transferring heat toward the space above sintering layer, and of the large amount of unburned carbon in upper sintering layer.

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Effect of Re-ignition Method on Sinter Yield Through Improving Carbon Combustion Ratio at Upper Layer of Sinter Packed Bed

Mechanical Properties and Microstructure of High Strength Steel for Fracture Suppression and High Absorbed Energy in Automobile Collision

Shinsuke Komine, Tatsuya Nakagaito, Shinjiro Kaneko, Yuki Toji, Tomohiro Sakaidani, Kentaro Sato

Abstract

A fundamental study on the axial crush performances of HSS (High Strength Steel) was carried out to clarify the effects of microstructure and mechanical properties on crashworthiness. Axial crush tests were performed to evaluate the crush performances of the HSS with different microstructures and mechanical properties and identify the fracture origins. The cracks in the press formed area were observed and the cracks led to the fractures. The high λ (Hole expansion ratio) steel showed excellent crush performances by crack suppression. Crash deformation in the press formed area was simulated by the ORB (Orthogonally Reverse Bending) fracture tests and the crack suppression factors were investigated. Through the ORB fracture test, it was clarified that the reduction of the hardness gaps between phases and the refinement of the hard phases (Fresh martensite) were effective for suppressing cracks in the press formed area. These microstructures were occurred by the Q&P (Quenching & Partitioning) process for increasing λ. Therefore, it was found that the microstructural design for increasing λ also contributed to excellent crush performances.

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Mechanical Properties and Microstructure of High Strength Steel for Fracture Suppression and High Absorbed Energy in Automobile Collision

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