ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
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Displaying 1-34 of 34 articles from this issue
Publication Data
Special Issue on "Frontier in Characterization of Materials and Processes for Steel Manufacturing"
  • Masanori Fujinami
    Article type: Preface
    2022 Volume 62 Issue 5 Pages 799
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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  • Shigeru Suzuki
    Article type: Review
    2022 Volume 62 Issue 5 Pages 800-810
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    This article reviews investigations on the formation of inhomogeneous ferrous (FeII) and ferric (FeIII) oxides in aqueous solution. These globally abundant materials are important in extensive fields of research including the corrosion of steels, mineralogy, environmental remediation, and biochemistry. Iron oxides are polycations consisting of FeII and FeIII ions bridged by hydroxyl groups and oxyanions. Solution conditions such as pH, temperature, the presence of foreign ions, and the presence of oxygen markedly influence the composition and structure of iron oxides and their transformation into various forms. Redox reactions of iron oxides are of great importance in controlling the extent of conversion between FeII and FeIII forms and the resulting composition of isolated species. Electrochemical potential versus pH (E–pH) diagrams are particularly useful in considering the details of iron oxide speciation as a function of solution conditions. Analytical techniques such as Mössbauer spectroscopy, X-ray diffraction, and electron microscopy are used to characterize the structure and morphology of iron-oxide samples. The involvement of mixed-valent (FeII/FeIII) species known as green rusts (GRs) in the formation of common iron oxides is described in terms of the oxidation level, pH, and foreign ion content of solutions. The terrestrial origin of iron oxides and their possible role in the abiogenesis of organisms also is described. Despite their inhomogeneity, the varied forms of iron oxides are important components of many natural and industrial processes.

    Diversity of multidisciplinary research on iron oxides. Fullsize Image
  • Susumu Imashuku, Kazuaki Wagatsuma
    Article type: Review
    2022 Volume 62 Issue 5 Pages 811-820
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
    Advance online publication: March 02, 2022
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    This paper reviews three emission spectrometric methods that can be applicable to the inclusion analysis in steel materials, which provides information on the number, the size and distribution, as well as the chemical composition of inclusion particles. Cathodoluminescence (CL), X-ray-excited optical luminescence (XEOL), and beam-scanning laser-induced breakdown spectrometry (LIBS) are employed for the imaging measurement of the inclusions. As a typical specimen, alumina inclusions are evaluated to compare their analytical performance. The easy handling and rapid response of them are significant features for an application to the on-site/in-line analysis in the production site of steel.

  • Toshiyuki Takahashi, Hotaka Kai, Nobumitsu Hirai
    Article type: Review
    2022 Volume 62 Issue 5 Pages 821-831
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Iron and steel slags are being used, on a trial basis, as environmental remediation agents for marine sediments in rocky coastal waters. In addition to chemical risk such as component leakage of slag into the environment, formation of biofilms is inevitable due to the adhesion of environmental microorganisms to slag surfaces. The transformation of free-living microorganisms into biofilm forms not only alters microbial behavior and various physicochemical tolerances, but also changes the properties of the material. However, the impact and effects of biofilms on materials remain unclear due to the challenges of performing detailed analyses of biofilms on materials such as chemically active slag. Therefore, in this study, slags coated with biofilms were prepared and their chemical effects were investigated to determine whether microbes improve slag function. Furthermore, prior to determining the effects of the slag coated with biofilm, quantitative evaluation techniques for assessing slag biofilms were developed. The review is specifically focused on accurate quantitative evaluation methods for assessing biofilms on slag. Additionally, changes in the chemical properties of slag-coated biofilms are summarized. This technique for modifying slags using microbial biofilm can be applied to the development of novel materials, not only for slag but also for other materials, as material processing and surface treatment technology.

  • Luca Chiari, Masanori Fujinami
    Article type: Review
    2022 Volume 62 Issue 5 Pages 832-839
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    The interactions between hydrogen, dislocations and vacancies that lead to the hydrogen embrittlement of iron-based materials have remained largely unknown with major impediments for the development of the infrastructure for hydrogen transport and storage. Recent studies of the hydrogen-induced lattice defects formed in pure iron and common austenitic stainless steels by positron annihilation lifetime spectroscopy have provided a breakthrough in understanding the controlling factors of the hydrogen embrittlement process. In this review, the main results of those studies are summarized and discussed together with current knowledge of hydrogen-related defects. The formation of vacancy-hydrogen complexes coupled to a plastic strain localization which is large enough to lead to hydrogen-enhanced vacancy clustering during the plastic deformation appears to be the likely factor that triggers the hydrogen embrittlement of bcc(α-) and fcc(γ)-iron.

  • Kazuhiko Yamada
    Article type: Review
    2022 Volume 62 Issue 5 Pages 840-848
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Multinuclear solid-state nuclear magnetic resonance (NMR) techniques are useful for structural investigations of insoluble and amorphous natural products, and have been gaining importance in coal chemistry. In addition to iron ore, coal is essential as steel raw material, but the physical properties of coal have remained unclear. Valuable information on coal, such as the cluster size, the chemical distribution of various functional groups, and the molecular structure, is potentially obtained by multinuclear solid-state NMR. This minireview is intended to introduce and discuss multinuclear solid-state NMR techniques, conventionally applied to coal characterizations. Some fundamentals of solid-state NMR are briefly explained. Representative applications of multinuclear solid-state NMR to coal, including carbon, nitrogen, and oxygen, are shortly described with their background and histories, and, zero-field solid-state sulfur NMR is proposed for the future application. This will be of interest to those who try to use multinuclear solid-state NMR techniques in coal chemistry.

  • Kenichi Nakayama
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 849-853
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    This article describes a procedure using flame atomic absorption spectrometry for specimen preparation to quantify tungsten in alloyed tool steel and high-speed steel. The sample solution was prepared using a microwave-assisted digestion with a mixed acid of hydrofluoric, nitric, and phosphoric acids. Vanadium was added as an internal standard element to the sample solution to measure tungsten and vanadium absorption lines simultaneously using a spectrometer equipped with a multi-wavelength system, which comprised a xenon lamp as a continuum light source and an echelle grating. The internal standard method, with its tungsten-to-vanadium absorbance ratio, contributed to accurate and precise quantification of high-content tungsten in tool steel samples.

  • Takashi Yamamoto, Ayumi Yamashita, Nozomi Yokoyama, Akira Yukumoto, Sh ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 854-859
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Supplementary material

    Sediment, soil and drainage water were collected at an abandoned copper mine, and the leachate copper prepared with 1M HCl were qualitatively analyzed by a handy elemental analyzer based on liquid electrode plasma atomic emission spectrometry (LEP-AES). Quantitative values obtained by the handy analyzer with standard addition or conventional calibration method combining with self-internal standard method, and ones by flame atomic absorption spectrometer were compared. The analytical condition for LEP-AES, the accuracy and the precision were discussed. The elongation of interval of pulsed applied voltage enhanced intensities of emission line, but background rising for copper emission line overlapping tail of broad OH band prevent expected improvement of the limit of detection. Copper species in sediment exist as divalent basic copper sulfate confirmed by XANES/EXAFS spectra recorded by a laboratory type spectrometer.

  • Daisuke Itabashi, Kazumi Mizukami
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 860-866
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
    Advance online publication: February 12, 2022
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    To determine the number density of fine precipitates in steels by asymmetric flow field-flow fractionation (AF4) with inductively coupled plasma–mass spectrometry (ICP–MS), an analysis method employing flow injection was investigated. For accurate calibration, matrix matching was performed by mixing the standard solution and AF4 carrier solution in front of a nebulizer. Two surfactants were used for AF4 separation; it was found that the appropriate selection of surfactants based on their acidity constant is essential to avoid salt precipitation. In addition, the effect of the AF4 retention time on recovery was investigated. A long retention time led to the adsorption and aggregation of the samples in the AF4 separation channel. Results showed that an AF4 retention time within 20 min facilitated superior recovery. Moreover, five types of AuNPs were analyzed via AF4–ICP–MS and quantified using flow injection analysis. Good analytical performance was achieved for all AuNPs and the recoveries exceeded 93%, and the coefficient of variation was within 5%. The effect of particle size on the recovery was not confirmed.

    Furthermore, the developed flow injection analysis for AF4–ICP–MS was applied to evaluate niobium carbide (NbC) precipitates in steels. The number density of nanometer-sized NbC was quantified to be within 1013 to 1014 particles per 1 g of Fe. It was quantitatively confirmed that the long-duration heat treatment led to an increase in the number density of nanometer-sized NbC. Hence, this method can be useful for quantitatively analyzing the size and number density of nanoprecipitates in steels.

  • Jun Kawai
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 867-870
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    In steel manufacturing process, one X-ray fluorescence analyzer with 40 crystal spectrometers is sometimes used for elemental compositional monitoring to control the process. The present paper is a suggestion to improve the performance of this bulk of X-ray fluorescence spectrometers by replacing the proportional/scintillation counters by silicon drift detectors (SDD) with digital signal processors (DSP). The wavelength dispersive X-ray fluorescence spectrometer with SDDs will enable the automatic adjustment of the optimal measuring condition. The shortcomings of both SDD and proportional counters are discussed.

  • Yuya Akahane, Sunfun Nakazawa, Shinsuke Kunimura
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 871-874
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    In this study, a method was presented for detecting low concentrations of elements in a high purity water sample using a portable total reflection X-ray fluorescence (TXRF) spectrometer. Preparing the dry residue of a sample droplet with large volume on a hydrophobic film coated sample holder was effective for improving the detection limit expressed as the concentration of a target element in a sample solution. When a TXRF spectrum of the dry residue of a 200 µL droplet of a solution containing 10 µg/L of Cr that was prepared by diluting a commercially available 1000 mg/L Cr standard solution with ultrapure water on a hydrophobic film coated sample holder was measured, a detection limit of 0.13 µg/L was achieved for Cr.

  • Peng Chen, Han Luo, Minchao Cui, Zhenzhen Wang, Yoshihiro Deguchi, Jun ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 875-882
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Accurate determination of sulfur (S) content in coke is of great significance to improve the quality of iron and steel. In this study, the sulfur in coke standard samples was detected in argon (Ar) atmosphere using laser-induced breakdown spectroscopy (LIBS), and S I 182.034 nm was chosen as the analytical line. The experimental results showed that it was advantageous to detect S in the early stage of plasma generation. Compared with tablet samples, the spectral intensities of binder samples on the copper foil tape were greater and the signal-to-noise ratio (SNR) was also greater. As for reduplicate experiments, the coefficient of variation (CV) of spectral intensities of binder samples was 10.58% and that of tablet samples was 88.54%. The plasma signal induced by binder samples was stronger and more stable. The internal standard method and support vector machine regression (SVR) were used to quantitatively analyze the sulfur content in binder samples, and SVR showed more accurate prediction accuracy. R2 of SVR with electron density and self-absorption correction was 0.965, root mean square error of prediction (RMSEP) was 0.18 wt.% and the limit of detection (LOD) was 0.026%. This result proved the applicability of binder for sulfur measurement in coke using LIBS.

  • Haorong Guo, Zhongqi Feng, Minchao Cui, Yoshihiro Deguchi, Liang Tan, ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 883-890
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    In recent years, metal additive manufacturing technology (also known as 3D printing) has achieved dramatic development and has gradually occupied an indispensable position in modern manufacturing. However, the purity and uniformity of the metal powder, which is the raw material for additive manufacturing, generate significant impacts on the performance of the product. Therefore, a rapid analysis method of the steel powders based on laser induced breakdown spectroscopy (LIBS) is investigated for the potential applications in 3D printing process. In the current experiment, two pretreatment methods of the novel adsorbing process and the traditional tableting process are employed for performing comparative study. Through the adsorbing process with conductive tape, the signal intensity of LIBS spectrum has been significantly enhanced. The crater topography demonstrates that the adsorption band samples can effectively overcome the shock wave effect of the laser induced plasma. The calibration curve of LIBS measurement indicates that the pellet samples can be easily affected by the plasma shock wave. Differently, the adsorption band samples are slightly influenced by the plasma shock wave. The determination coefficient and data stability of the calibration curve are better in the condition of adsorption band samples. Through the simulated quantitative analysis with totally 11 artificial steel powder samples, the analytical performance of the two sample pretreatment processes is compared. Manganese (Mn) is selected as the target element with the matrix element of iron (Fe). When compared with the pellet samples, the average value of Relative Error of Prediction (REP) is reduced from 7.73% to 1.36% and the average value of Relative Standard Deviation (RSD) is reduced from 20.34% to 6.22% for the adsorption band samples. Based on the experimental results in the current work, it can be verified that the adsorbing process is a promising sample pretreatment method for steel powders. Moreover, this provides an effective sample pretreatment method for LIBS analysis of steel powder for 3D printing.

  • Susumu Imashuku, Kazuaki Wagatsuma
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 891-896
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Removal of Al2O3 and MgO·Al2O3 spinel inclusions is a critical issue in the production of stainless steel. Understanding the formation mechanism of these inclusions is important for facilitating their removal. Electron probe microanalysis (EPMA) has been widely used to understand their formation mechanism. However, using EPMA to identify inclusions with agglomerated MgO·Al2O3 spinel and Al2O3 inclusions or agglomerated MgO·Al2O3 spinel and MgO inclusions is difficult because of the wide composition range of MgO·Al2O3 spinel. This study presents a novel analytical method to distinguish among MgO·Al2O3 spinel, MgO, and Al2O3 in these agglomerates based on the differences in their emission colors in cathodoluminescence (CL) imaging. Al rich and stoichiometric MgO·Al2O3 spinel inclusions were distinguishable by detecting the green luminescence in CL images in the wavelength regions of 350–1000 nm and 395–575 nm, respectively. In contrast, MgO and Al2O3 inclusions emitted red luminescence in the wavelength region of 350–1000 nm but no luminescence in the wavelength region of 395–575 nm. In addition, MgO inclusions with small particle sizes, which were agglomerated with MgO·Al2O3 spinel inclusions, were detected based on broadening around 750 nm corresponding to the CL peak at 690 nm. The proposed method could lead to a better understanding of the formation mechanism of Al2O3 and MgO·Al2O3 spinel inclusions in stainless steels.

  • Tomoharu Ishida, Katsumi Yamada, Katsuhisa Yamauchi
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 897-903
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Fine precipitates in steel have various effects on the properties of steel products. Therefore, it is important to investigate the state of existence of precipitates in steel in order to consider their effect on the material. In this study, the size and shape of Nb and V precipitates were observed by electron microscopy and the amount of precipitates was evaluated by electrolytic extraction analysis in martensitic stainless steels which has excellent heat resistance. For steels with a certain chemical composition, stable chromium nitride (Cr2N) formation was observed when only Nb was added, whereas combined addition of Nb and V suppressed the formation of Cr2N and produced extremely fine precipitates in the steel (in lath martensite). The fine precipitates could be observed in thin film samples by using a high-resolution transmission electron microscope (TEM). In order to evaluate the state of formation of the fine precipitates in the steel quantitatively, the difference in the precipitation behaviors between the two materials was investigated by the size-classified quantitative analysis method. This method is considered to be a useful analytical technique in the development and design of high performance steels using fine nitrides and carbides with sizes of the several nm order.

  • Kouki Maeda, Shigeru Ueda, Ryo Inoue
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 904-911
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    The conventional recovery technology is not economically viable due to the low rare metal concentration in industrial scraps. It is expected that iron- and steelmaking process can recover rare metals as a high-concentration ore substitute. For efficient enrichment of rare earth metal (REM) in this process, the establishment of the thermodynamic values related to REM deoxidation of molten iron is required. To obtain precise thermodynamic data, the concentration of elements solved in the metal sample should be determined separately from that in the inclusions, which is suspended in molten iron. Therefore, a stable extraction method for REM oxide in iron was investigated.

    From the dissolution behavior of Sm2O3, Nd2O3 and Dy2O3 reagents in various eluents, 2 v/v% triethanolamine-1 w/v% tetramethylammonium chloride-methanol (2%TEA) is most suitable for the extraction of REM oxide. From the analysis using SEM-EDX and SEM-WDX, REM oxide in Fe-0.2 mass% REM alloy was identified as REM2O3 containing a small amount of MgO and FeO. From the relationships between the total O concentration and the insoluble O concentration calculated from insoluble REM concentration, the REM oxide inclusions in Fe-REM alloy could be extracted precisely by the electrolysis with 2%TEA.

  • Masahito Uchikoshi, Daisuke Akiyama, Ken’ichi Kimijima, Kozo Shinoda
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 912-921
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Supplementary material

    Knowledge of the distribution of metal chloro complexes in hydrochloric acid solutions is fundamental for constructing an efficient hydrometallurgical process. The condition of chemical species in the aqueous phase is important for understanding adsorption reactions as well as the properties of functional groups. The distribution of ferric aqua and chloro complexes was determined by fitting thermodynamic models to a series of UV-vis absorption spectra. In addition, X-ray absorption spectra of individual species were obtained by decomposition of a series of raw spectra by the distribution of ferric aqua and chloro complexes, and each structure was determined. Analyses using the UV-vis and X-ray absorption spectra complement each other and offer more reliable results than the conventional methods. Five ferric aqua and chloro complexes of [FeIII(H2O)eq4(H2O)ax2]3+, [FeIIIClax2(H2O)eq4]+, [FeIIICleq3(H2O)ax2]0, [FeIIICl4], and [FeIIICleq4Clax2]3– were observed and the thermodynamic parameters of the formation reactions were successfully determined.

    The structures of the ferric aqua and chloro complexes in hydrochloric acid solutions. (Online version in color.) Fullsize Image
  • Nobuo Uehara, Mina Sasaki, Arinori Inagawa
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 922-928
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Magnesium oxide (MgO) contained in steelmaking slags in its liberated form, referred to as free MgO, expands when hydrated. The expansion of free MgO sometimes causes the deterioration of steelmaking slags used as construction materials for roads. Therefore, a method that determines the free MgO content in steelmaking slags is required. Solvent extraction is a promising preparation method for determining free MgO in steelmaking slags. Herein, organic solvents were explored for their extraction capabilities, and MgO was successfully extracted with 2,2,2-trichloroethanol (TCE) at 140°C over 3 h. TCE could not be used to extract any other magnesium compounds in blast furnace slags or merwinite, which contain no free MgO, indicating that free MgO was selectively extracted with TCE. The MgO content determined by TCE extraction and atomic absorption spectrometry was found to be reasonably consistent with that determined by other methods, which implies that this method is suitable for measuring the MgO content in steelmaking slags. The mechanism for the extraction of MgO by TCE was also investigated, and it was found that TCE extraction occurred via an acid-base reaction and an oligomerization crosslinking reaction.

  • Toshiyuki Takahashi
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 929-940
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
    Advance online publication: February 24, 2022
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    To evaluate microbial potentials for the material development of iron and steel slag, this study particularly investigated the chemical effect of slag, which was artificially coated with a microbial biofilm, on buffer action. Prior to evaluating the slag, this study also developed a method to determine the amount of microbes adhering to slag. To encourage the growth of Bacillus bacteria on slag, the slag was mixed with the bacteria in LB medium for 24 hours. After extracting microbial DNA using the hot-alkaline DNA extraction method, the microbial quantity attaching tightly to slag was determined from the concentration of the microbial DNA using Pico Green-based fluorometry. The adsorption isotherm between the microbial quantity attached to the slag and the corresponding reacting microbial amount was analyzed using the Langmuir and Freundlich adsorption models. To examine the buffering action of slag coated with and without microbes, each slag was immersed in distilled water for seven days. Next, both pH levels of each slag-containing solution and each amount of microbes attached to slag were determined. The pH increased in both solutions containing slag coated without biofilm and with partially desquamated one; in contrast, the slag coated with well-preserved biofilm showed a buffering action, resulting in an inhibited increase in pH. These results show that slag coated with biofilm is distinctively different from an original slag coated without biofilm in terms of buffer action. This processing technique using microbes could contribute to the development of a novel application of slag as a recycled material.

  • Susumu Imashuku, Kazuaki Wagatsuma
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 941-947
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Supplementary material

    In developed countries, nearly half of steelmaking slag is reused in road construction. Determining free lime content in steelmaking slag is important because the hydration of free lime can result in the road fracturing. Recently, we have developed a simple method to rapidly determine the area fraction of free lime via cathodoluminescence (CL) imaging of steelmaking slag based on orange illuminated areas corresponding to free lime. However, the areas of free lime that precipitated along grain boundaries of wüstite were overestimated in CL images because the thickness of the precipitated free lime was not evaluated properly. In this study, we investigate the grain-boundary microstructures of wüstite and propose a method to correct the overestimated areas of the free lime. Scanning transmission electron microscope observation revealed that the average thickness of free lime precipitated in the grain boundaries was 250 nm, which was approximately 20 times smaller than that evaluated via the CL image. Assuming that the thickness of the free lime precipitated in the grain boundaries was 250 nm as a whole, the area fractions decreased by 60%–80%, compared with those without the thickness correction. Considering the CL sampling depth of a few microns, the proposed method can determine the volume fraction of free lime in steelmaking slag more precisely, hereby aiding in the prevention of road expansion in the reuse of steelmaking slag.

  • Yuki Hata, Hideyuki Hayashizaki, Toshimasa Takanohashi, Takafumi Takah ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 948-956
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Supplementary material

    The chemical structure models for the extractions and residues of two types of bituminous coals, A and B, were constructed. The molecular weights of the extractions were determined via gel permeation chromatography (GPC). New standard materials with structures similar to those of coal extraction (i.e., 9, 10- diphenylanthracene, 5,6,11,12-tetraphenylnaphthracene, and chemical compounds A (Mw = 811) and B (Mw = 1135), which were synthesized using the coupling reaction) were adopted for GPC in order to obtain more accurate mean molecular weights than those in literature. Furthermore, a support program for constructing chemical structure models based on 1H nuclear magnetic resonance (NMR) spectra was adopted. The coal models constructed suitably indicate the differences between the types of coal. In particular, it is found that a high pyridine-insoluble fraction extracted rate, which accounts for the most significant difference between the total extracted rates for coals A and B, enhance the coking property of coal A. In addition, the cluster size in the magic solvent-insoluble fraction might affect the softening property of coal.

  • Shigeru Suzuki, Kazuhiro Mizusawa, Toru Kawamata, Rie Yamauchi Umetsu, ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 957-962
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Tensile tests and electron backscatter diffraction (EBSD) measurements were performed to understand the microscopic processes in the plastic deformation of Fe–17-at%-Ga alloy single crystals with a body-centered cubic (BCC) structure. Samples close to the [001], [012], and [011] orientations for the tensile directions were cut from the alloy single crystal grown by the Czochralski method. They were plastically deformed at room temperature. The surface morphologies and microstructures of the deformed samples were characterized using an EBSD instrument attached to a scanning electron microscope. The mechanical properties such as elasticity and flow stress depended on the crystal orientation. Slip by dislocation glide was dominant in the tensile deformation in the [011]-oriented sample. Coarse planar deformation twins were observed in the [001]-oriented sample by plastic deformation. Thin deformation twins and slips were observed in the [012]-oriented sample. This implies that deformation twins have an important role in the plastic deformation of alloys. Although the addition of Ga induces solid solution hardening of iron-based alloys, the characteristic microscopic processes in the plastic deformations of the present alloys are similar to those in the plastic deformations of BCC iron and its alloys.

  • Shun-Ichiro Tanaka, Shigeo Sato, Kengo Matsuda, Masaki Chiba, Shigeru ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 963-969
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Microscale changes in the microstructure of and stress distribution in a polycrystalline duplex stainless steel comprising ferrite and austenite caused by plastic tensile deformation are characterized to understand the microscopic processes of the crystal plasticity of dual-phase steel. Because the ferrite of the body-centered-cubic structure and the austenite of the face-centered-cubic structure exhibit different mechanical properties, texture changes in the ferrite and austenite caused by uniaxial tensile deformation are investigated based on the electron backscatter diffraction pattern. Residual stresses formed by tensile deformation are characterized using a two-dimensional method based on X-ray diffraction. The results show that the steel exhibits a banded microstructure of ferritic coarse grains and austenitic fine grains, and that the texture is changed by tensile deformation. The grains in the steel are rotated by tensile deformation depending on their orientation with respect to the tensile axis. Residual stress measurements demonstrate that compressive stresses remain in the elastically hard ferrite after tensile deformation, whereas tensile stresses remain in the austenitic phase. The formation of the residual stresses are discussed based on the characteristic microscale plasticity of ferrite and austenite.

  • Masahito Uchikoshi, Kengo Matsuda, Yusuke Onuki, Kozo Shinoda, Shigeru ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 970-976
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    A series of tensile tests of polycrystalline high purity iron were carried out in order to trace microscopic orientations in different grains during plastic deformation. Crystal rotations were classified into two stages: one was the initial stage to the maximum strength or onset of necking, and the other was the subsequent stage from necking to fracture. Before the necking, two types of grain were observed: one rotated toward the [011] direction and the other did not rotate. During necking or plastic instability, the grains near the necking rotated toward the [111] direction. Activation of only a single slip system at the early stage did not follow the Taylor model which assumes multiple slip systems were active during deformation. In addition, it was observed that one grain was divided into two grains because a part of the grain rotated and the rest of the grain hardly rotated. Precise prediction of deformation of bcc metals requires improvement of the Taylor model by considering the transition of a single slip system to a multiple slip system, and a constraint on crystal rotation caused by adjacent grains. Necking due to tensile deformation was observed in grains oriented toward the [011] direction and local areas close to the necking or plastic instability finally rotated toward the [111] direction when the specimen fractured. Such rotation was also observed in a single crystal tensile test, because the lattice was released from various constraints on rotation.

  • Piyada Suwanpinij, Margarita Bambach, Atipong Bootchanont, Wutthigrai ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 977-983
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Supplementary material

    This paper studied the copper precipitation in an 18CrNiMo7-6 martensitic steel (0.19 mass% C) with copper addition and its resulting improved mechanical behavior. The development of nano-precipitates in two modified alloys with 1.0 and 1.5 mass% copper addition was investigated by means of synchrotron X-ray absorption spectroscopy. The first-principles calculation has enabled the modeling of the unavailable copper standards: solid solution, B2, BCC, 2H, 9R and 3R, for calculating the XAS spectra and successfully identified the unknown phases after aging for the first time in this steel group. The samples alloyed with 1.5 mass% copper yielded the semi-coherent 9R structure when aged at 500°C between 166 to 360 minutes. The ones containing 1 mass% copper formed the B2 ordered structure after aging at 480°C for 50 minutes and revealed the co-existence of the 9R after 240 minutes. The analysis reveals the precipitation kinetics of copper in low carbon martensitic steel and helps determine the optimum tempering parameters to adjust peak strength.

  • Shunsuke Taniguchi, Genichi Shigesato, Masaaki Sugiyama
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 984-991
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Controlling the precipitation of alloy carbides with sizes of a few nanometers in ferritic steels is one of the important issues for designing of high strength steels. In this study, the interfacial atomic structures of nanometer-sized titanium carbides (TiC) in 0.05C-0.5Mn-0.1Ti-3Al (mass%) ferritic steels are investigated using scanning transmission electron microscopy. Plate-like TiC precipitates satisfying Baker-Nutting orientation relationship with the ferrite matrix are observed. High angle annular dark field scanning transmission electron microscopy with atomic resolution reveals the arrangement of Ti atomic columns in TiC and Fe atomic columns in the ferrite matrix. The TiC platelet with ~8 nm in length and ~1 nm in thickness has a coherent planar interface, which length is over the transition size from the lattice mismatch model. The semi-coherent TiC with ~14 nm in length and ~4 nm in thickness has the ledges with misfit dislocations on the planar interface. The lattice spacing of TiC along the coherent planar interface is found to be smaller than the lattice spacing of the semi-coherent broad interface or the value calculated from the lattice constant of bulk TiC.

  • Takuya Mori, Takahiro Ozawa, Yuki Hiruta, Seigo Matsunaga, Kazunori Fu ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 992-997
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
    Advance online publication: February 05, 2022
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    In this study, using two-dimensional X-ray absorption fine structure (2D-XAFS), the structures of atmospheric corrosion products on the steel surfaces were observed in the cross-sectional direction. For 2D-XAFS measurement, the sample was sliced from the surface of the rust toward the substrate using a microtome and thinned below 10 µm. In addition, the 2D-XAFS data incorporated an unsupervised learning denoising method based on the Noise2Noise algorithm for achieving high spatial resolutions. The results demonstrate that the structure of the amorphous rust exhibits an α-FeOOH-like structure, and the analysis of the composition ratio of Fe3O4, α-FeOOH, and γ-FeOOH revealed the distribution the Fe3O4 ratio. This distribution provided compelling evidence for proceedings of the reactions suggested by Evans et al. during the atmospheric exposure test.

  • Hiroyuki Uchima, Masayoshi Kumagai, Junzo Shimbe, Akihiro Tanabe, Yuta ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 998-1003
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
    Advance online publication: January 07, 2022
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    Middle-carbon martensite steels are vital materials for mechanical components and their mechanical properties have attracted significant interest. However, the decrease in the elastic limit of the as-quenched materials is one of the remaining puzzles. Herein, we quantitatively characterized the dislocation density and its structure in the as-quenched and tempered martensite steel by neutron diffraction line profile analysis and discussed their impact on the yield stress. The dislocation density in the as-quenched specimen was the highest at 9.7 × 1015 m−2, while it decreased with an increase in the tempering temperature. In addition, the component ratios of edge and screw dislocations decreased and increased, respectively, depending on the increase in the tempering temperature. The dislocation arrangement parameter (M) varied between the tempering temperatures of 220 and 290°C. Although there was a large difference between the yield stress obtained from the tensile test and that estimated from the dislocation density, the experimental results could be explained by correcting them with the inverse of M value as an index showing the effective dislocation density ratio.

  • Kodai Murasawa, Kota Ueno, Yoshinori Kusuda, Masato Takamura, Takayuki ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 1004-1012
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Stress relaxation, which occurs during holding at the bottom dead center in press forming, affects press formability. Because holding at the bottom dead center is completed within several seconds, it is important to predict the stress relaxation behavior of the first few seconds after the start of holding. The purpose of this study is to propose a model, the material parameters of which are obtained from tensile tests, to predict the stress decreasing behavior in the early stage of stress relaxation in steel sheets. We constructed the model by modifying the Kocks-Mecking model based on the following assumptions: Stress relaxation at room temperature is due to the slip motion of dislocations, which indicates that the plastic strain rates at the start of stress relaxation are same as those in the previous tensile process. In this study, it was assumed that the change in microstructure during stress relaxation is negligible; hence material parameters remain constant during stress relaxation. The measured and predicted stress relaxation behaviors for various strain rates during the tensile process were compared. It was observed that an increase in the plastic strain rate during the tensile process accelerated stress relaxation. The proposed model was able to predict this phenomenon. However, the relative error between experimental results and the model increased as the stress relaxation progressed mainly owing to dynamic strain aging. Therefore, the proposed model is applicable in the condition when effect of dynamic strain aging is negligible.

  • Chihiro Iwamoto, Masato Takamura, Kota Ueno, Minami Kataoka, Ryo Kurih ...
    Article type: Regular Article
    2022 Volume 62 Issue 5 Pages 1013-1022
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    Neutron diffraction is a powerful non-destructive method for evaluating the microscopic structure and internal stress of metal plates as a bulk average. Precise neutron diffraction measurements with a high-intensity neutron beam have already been carried out at large-scale neutron facilities. However, it is not easy to provide users with enough experimental opportunities. We are working on upgrading the neutron diffractometer with techniques of time-of-flight to enable stress measurements at RIKEN accelerator-driven compact neutron source (RANS). To improve neutron diffraction resolution, delayed neutrons, which expand neutron beam pulse width, should be suppressed. However, it is difficult to separate the delayed neutrons experimentally. In this study, a new analysis method has been proposed to deconvolute the diffraction peak from the delayed neutron component. Moreover, a new collimator system, called decoupled collimator system, has been developed to reduce the number of delayed neutrons. The diffraction patterns from a powder sample of pure body-centered cubic iron were measured with the decoupled collimator and the diffraction peak of {211} reflection was analyzed by the new analysis method using a model function of a single exponential decay function convoluted with a Gaussian function. By this method, the decoupled collimator system has been confirmed to achieve a smaller measurement limit of lattice strain Δε than a small-aperture polyethylene collimator system and a non-collimator system. The currently available Δε was 6.7×10−4, this means that the internal stress up to 130 MPa can be well evaluated for steel materials with a Young’s modulus of 200 GPa at RANS.

  • Kenichi Nakayama
    Article type: Note
    2022 Volume 62 Issue 5 Pages 1023-1026
    Published: May 15, 2022
    Released on J-STAGE: May 24, 2022
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    This paper describes an improved microwave digestion procedure for steel samples of various kinds intended for inductively coupled plasma atomic emission spectrometry, including low alloy steel, stainless steel, alloyed tool steel, and high-speed steel. Their resulting solutions were used for the simultaneous quantification of alloyed elements together with several light elements of boron, aluminum, silicon, and phosphorous. Conventional digestion methods, using materials such as hydrochloric and nitric acids including aqua regia, and sulfuric and phosphoric acids with a fuming treatment, showed poor ability to decompose certain steels completely or to be simultaneously quantified with some elements. By contrast, microwave digestion with an acid mixture of hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid, and distilled water with a 2:1:1:1:5 volume ratio fully decomposed various steel samples. For inductively coupled plasma atomic emission spectrometry, the suggested procedure is applicable to quantify boron, aluminum, silicon, phosphorous, titanium, vanadium, manganese, cobalt, copper, molybdenum, and tungsten.

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