Online edition：ISSN 2188-0921
Print edition：ISSN 0913-4794
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Errata added (April 27, 2023)
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Prediction and Measurement Technologies of Material Structure and Properties, the Technologies Supporting Kobelco Group's Material Development
First-principles Calculations on Co-segregation of P and Transition Metal Elements at Fe Grain Boundaries
P.01
Shinya MORITA
The first-principles (ab-initio) calculations based on the FeΣ3 (111) grain boundary model have been used to study the effects of transition metal elements, Cr, Mn, and Mo, on the grain-boundary co-segregation and of P contained in the steel and on the grain-boundary embrittlement. It has been found that Cr, Mn, and Mo indicate repulsive interactions with P at the grain boundaries of Fe and that the shorter the distance to the P atom, the stronger the repulsive interactions become. The interactions have turned out to be small relative to the grain boundary segregation energy of P, causing only a small effect on the segregation behavior of P. However, Mo, when segregated on the grain boundaries, increases the binding energy of the grain boundaries, and is expected to suppress the grain-boundary embrittlement due to P.
Multiscale Elasto-plastic Finite Element Analysis of Dual-phase Steel Based on Homogenization Method
P.07
Dr. Eisuke KUROSAWA
High tensile steel, such as dual-phase steel consisting of ferrite and martensite, is still widely used in several industries. From a research and development point of view, it is important to clarify the relationship between microstructure and macroscopic mechanical properties. In this study, samples of dual- or single-phase steel consisting of similar constituent phases were experimentally produced, and their tensile properties were obtained by material testing. These data were introduced into the microstructure model generated by an image-based modeling method using SEM observation imaging. Using this model, multiscale FE simulation based on homogenization elasto-plasticity theory was conducted, and validation was investigated by comparison with experimental results.
Technology for Predicting Residual Stress in Extruded Members of 7000 Series Aluminum Alloy Considering Heat Treatment Process
P.13
Hiroaki HOSOI
Extruded members of 7000 series aluminum alloy, which has the highest 0.2% proof stress among aluminum alloys, is effective for automotive weight reduction. However, its high sensitivity to stress corrosion cracking (SCC) makes it important to manage residual tensile stress in the members. This paper describes an equation to predict residual stress after artificial aging treatment or after the paint baking process from the residual stress caused by plastic forming during T1 tempering of 7000 series aluminum alloy on the basis of the creep test results of 2 types of newly developed alloys and an extruded material made of standard 7003 alloy. It has been clarified that the artificial aging and paint baking process for extruded members of 7000 series alloy significantly reduce the tensile residual stress caused by plastic forming during the T1 tempering, reducing the risk of SCC.
Analysis of Hot Crack and Welding Deformation during One-side Butt Welding Using Idealized Explicit FEM
P.20
Tsuyoshi MIWA, Dr. Kei YAMAZAKI, Kensaku NISHIHARA, Dr. Masakazu SHIBAHARA
This paper reports on the analyses by idealized explicit FEM of hot crack and welding deformation during one-side butt welding. In the hot crack analysis, the incremental value of the plastic strain generated in the brittle temperature range (BTR) and the temperature gradient vector have been evaluated as the occurrence index of hot cracks. By comparing these with the results of welding experimentation, the validity and effectiveness of the hot crack occurrence forecasting by this analysis method have been examined. In the deformation analysis, the actual structure size level has been examined for one-side submerged arc welding (FCB™ method) and one-side tandem welding (HT-MAG™ method). It has been shown that the application of these analysis methods has enabled deformation forecasting at high speed and with high accuracy even in large-scale analyses, which hitherto have been difficult.
Battery Degradation Modeling Based on FIB-SEM Image Features Extracted by Deep Neural Network
P.29
Dr. Yoichi TAKAGISHI, Dr. Tatsuya YAMAUE
Attention is being paid to attempts at predicting the degradation and life of lithium-ion batteries (LIBs). This paper focuses on the examination conducted on the features, advantages, disadvantages, etc., of a data-driven prediction model that combines feature extraction and regression by deep learning. Also described is a physics-based model that predicts the degradation progress by electrochemical reaction formula and the like. As a result, it was found that in the physics-based model, the prediction accuracy is high when the degradation phenomena are relatively straightforward, but its application is difficult when the phenomena are complicated or unknown. On the other hand, the data-driven modeling can be done even when the phenomena are not sufficiently clear and is considered to have a great advantage in predicting degradation accurately. Further consideration of the constructed model has also turned out to be useful for elucidating hidden phenomena.
Technology for Analyzing Solute Carbon in Retained Austenite Using Soft X-ray Emission Spectroscopy
P.35
Dr. Aya HINO, Keiko YAMADA
An attempt has been made to measure the microscopic distribution of carbon concentration and to analyze the results using a soft X-ray emission spectroscopy analyzer installed in a scanning electron microscope. The obstacle to accomplishing this was the organic substances adhering to the sample surfaces and acting as contaminants. However, a technique has been established for analyzing while removing contamination by gas-cluster ion beam irradiation, which has enabled carbon distribution measurement focusing on the microstructure in steel. It has also been suggested that this technique may be used for the analysis of the binding state of carbon contained in steel.
Technology of Evaluating Minute TiN Inclusions in High-carbon Steel Wire Rod for Advanced Applications
P.40
Takashi SUGITANI, Atsuhiko TAKEDA, Takehiro SHUDO, Dr. Hiroki OTA, Masaki SHIMAMOTO, Yoshiki TAKEDA
In high-carbon steel wire rod to be drawn into fine diameters, it is necessary to suppress breakage caused by inclusions during the wire drawing process. In the past, breakage in high carbon steel wires was mainly due to alumina inclusions. However, with the higher reduction in the diameter of wires, breakage started from titanium nitride (hereinafter referred to as TiN), which is more minute than alumina, has become remarkable. To study the means for suppressing TiN and to verify their effects, it is necessary to establish both a technique to analyze the ultra-low concentration of Ti dissolved in steel and a technique to evaluate the number of TiN inclusions. This paper describes a method for quantifying concentration of dissolved Ti using a secondary ion mass spectrometer owned by the Kobe Steel group and a technique for evaluating the number of TiN particles, which has been newly developed by applying a chemical extraction method. This paper also describes how the correlation between the number of TiN particles and the frequency of wire breakage has made it possible to predict the quality of extra fine wires.
Various Functional Materials and Supporting Technologies in KOBELCO Group
Benefit Estimation of Soft-magnetic Pure Iron by Magnetic Field Analysis Considering Effect of Forging Strain
P.47
Shingo KASAI, Dr. Masamichi CHIBA, Shinya MORITA, Takumi KITAYAMA
The movement toward carbon neutrality is expanding as a result of heightened environmental awareness. For soft-magnetic materials, whose usage is expected to increase as electrification progresses, the omission of the heat treatment step called magnetic annealing is regarded as one of the measures for reducing the amount of CO2 produced by the manufacturing process. Kobe Steel's soft-magnetic pure iron, the ELCH2 series, has magnetic properties comparable to those of the magnetic-annealed material of low-carbon steel, even without magnetic annealing, and is being looked to as a non-heat-treated material of low-carbon steel. Using forging analysis and magnetic field analysis, a comparison has been made among the component characteristics when a solenoid iron core is changed from magnetic-annealed material of low-carbon steel to as-cold-forged material of ELCH2. This paper introduces the results indicating that the ELCH2, even if the magnetic annealing is omitted, achieves the same electromagnetic force at low current and also achieves higher electromagnetic force at high current than what is achieved by the magnetic-annealed material of low-carbon steel.
Axial-gap Motor Using Thin Wire of Soft-magnetic Pure-iron
P.52
Shinya MORITA, Takuya MATSUMOTO, Shingo KASAI
Since wires of soft-magnetic pure-iron have high magnetic flux densities, they are used for the iron cores of electromagnetic parts for DC-driven components such as electromagnetic relays and solenoids. It has been difficult, however, to apply them to AC-driven components, such as motors, due to the skin effect and eddy current caused in the material. The application to a motor has been examined by decreasing the diameter of the wire of soft-magnetic pure-iron to reduce the eddy current loss. This paper reports the results of a prototype of an axial-gap motor with a new structure using a wound-on iron core of the hexagonal thin wire of pure iron.
Technology for Improving Performance of Tin Plating for Automotive Terminals
P.57
Yutaro UEDA, Masahiro TSURU
Copper alloy, which has excellent electrical conductivity, is widely used for automotive terminals. Since copper alloys are oxidized in the atmosphere, and their oxide coating acts as electrical resistance, tin plating is applied to keep the contact resistance low. This paper explains the characteristics required for the tin plating of automobile terminals and introduces Kobe Steel's original tin-plated products with new reflow plating (high thermal resistance and low friction).
Stabilization of Characteristics by Hydrogen Plasma Treatment for Top-gate Thin-film Transistor Using High-mobility Oxide Semiconductor, a-IGZTO
P.65
Dr. Kohei NISHIYAMA, Dr. Mototaka OCHI, Yumi TERAMAE, Hiroshi GOTO
Top-gate thin film transistors (TFTs) using a high mobility oxide semiconductor, amorphous In-Ga-Zn-Sn-O (a-IGZTO), are attracting much attention in the field of flat panel displays. Here, the effectiveness of hydrogen plasma treatment for the formation process of low electrical resistance source/drain has been clarified. The hydrogen plasma treatment has reduced the sheet resistance of an a-IGZTO film, and this low resistance state has demonstrated high stability under heat treatment. An X-ray photoelectron spectroscopy confirmed the OH group's existence after argon plasma irradiation, suggesting that a-IGZTO has been physically sputtered. Meanwhile, it has been shown that hydrogen plasma irradiation causes the a-IGZTO to be reduced by hydrogen radicals, the reduction reaction producing metallic components. This reduction reaction is considered to have made the top-gate type TFT treated by hydrogen plasma more stable under heat treatment.
Technical Trends in, and Analysis of Evaluation Technologies of Secondary Batteries
P.71
Dr. Takayuki TSUBOTA, Dr. Takashi ACHIHA, Yoshiki HAYASHI, Dr. Takuya MORI, Hiroshi OZONO, Hidemasa TSUNEISHI
The shift toward electric vehicles (EV shift) is being accelerated worldwide to reduce CO2 emissions during running. In addition, more renewable energy is being introduced, increasing the demand for secondary batteries. Against this backdrop, studies are being conducted to increase the energy density of lithium-ion batteries for EVs and stationary battery storage. The company is also focusing on developing new batteries, e.g., all-solid-state batteries that can further improve energy density and sodium-ion batteries that use sodium instead of lithium, a rare metal. Kobelco Research Institute supports the development of batteries through its evaluation/analytics technologies, including "the prototype production of lithium-ion batteries, allsolid-state batteries, and sodium-ion batteries," "battery characteristics evaluation technology," "reaction distribution analysis technology in battery cells," "redox reaction analysis technology," and "non-destructive deterioration diagnosis technology for reuse," thus contributing to the realization of carbon neutrality.
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Errata added (April 27, 2023)
Recent Development Trends in Materials for Bipolar Plates of Proton Exchange Membrane Fuel Cells (PEMFCs) and Kobe Steel's Activities
P.79
Toshiki SATO
Proton exchange membrane fuel cells (PEMFCs) are expected to become clean energy sources for transportation applications. Their bipolar plates, which are crucial parts of PEMFCs, significantly affect the durability, power-generation performance, and cost of PEMFCs. Thus, much effort has been made to improve the durability and performance of bipolar plates and reduce their costs. To improve the corrosion resistance and interfacial contact resistance (ICR), which affect the durability and characteristics of bipolar plates, Kobe Steel has been developing coated titanium using an unprecedented film and process since 2004. This paper reviews the recent development of carbon-polymer composites and coated metals, considered materials for bipolar plates, while focusing on their corrosion resistance and ICR. Also described is Kobe Steel's effort to develop film for titanium bipolar plates.
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