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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 61 (2021), No. 7

  • Opportunity and Challenges of Iron Powders for Metal Injection Molding

    Abhijeet Premkumar Moon, Srinivas Dwarapudi, Kameswara Srikar Sista, Deepak Kumar, Gourav Ranjan Sinha

    pp. 2015-2033

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    DOI:10.2355/isijinternational.ISIJINT-2021-050

    Abstract

    Design flexibility, mass customization, waste reduction and the ability to manufacture near-net complex-shape structures, as well as rapid prototyping, are the main advantages of Metal Injection Molding (MIM). A brief review of the MIM technique, materials and their development to trending applications using iron powders was delineated. The ground-breaking applications of MIM in automotive, medical, and magnetic materials were discussed. The current-status of iron powder product development prepared for MIM was reviewed. In addition, this paper discussed the main processing challenges considering the MIM technology for producing high-end applications. Overall, this paper gives a summary of MIM, including a study on its benefits and opportunities and as a roadmap for future research and development in iron and steel powder manufacturing technique.

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    3. Effect of Intercritical Deformation on Bainite Formation in Al-containing TRIP Steel ISIJ International Vol.43(2003), No.8

  • Modelling of Defluidization of ZrO2/Fe Particles in High Temperature Gas Fluidization: Influence of Fe Contents

    Jianbo Zhang, Zhan Du, Chuanlin Fan, Feng Pan

    pp. 2034-2040

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    DOI:10.2355/isijinternational.ISIJINT-2021-028

    Abstract

    The contents of Fe on the surface of iron ore fines had a great influence on the fluidization behavior during high temperature fluidized bed reduction, which would cause defluidization when exceeding a critical value. In this paper, simplistically, ZrO2/Fe particles with different Fe contents on the surface were used as raw materials. Through modification of previous models, a quantitative relationship was established to predict the defluidization temperature of ZrO2/Fe particles with different Fe contents, and the calculation results corresponded well with the experimental data obtained from the defluidization test. The model in this paper firstly explained the dependence of defluidization behavior on the contents of Fe in high temperature gas fluidization, and it could well predict the metallization degree of commercial iron ore fines when defluidization occurred during fluidized bed reduction. Therefore, the model could be used as a reference to select suitable operating conditions for treating fine iron oxide particles in high temperature gas fluidization processes, such as direction reduction and chemical looping.

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    1. Generation of Pyroxene-Based Porous Ceramics from Steel Refining Slag ISIJ International Vol.61(2021), No.7
    2. Opportunity and Challenges of Iron Powders for Metal Injection Molding ISIJ International Vol.61(2021), No.7
    3. Numerical Simulation of Particle Mixing Behavior in High Speed Shear Mixer and Cylinder Mixer ISIJ International Vol.61(2021), No.7

  • Generation of Pyroxene-Based Porous Ceramics from Steel Refining Slag

    Yu Li, Weitao Tang, Hongjian Sheng, Yindong Yang, Alex Mclean

    pp. 2041-2047

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    DOI:10.2355/isijinternational.ISIJINT-2021-043

    Abstract

    In this paper, porous ceramics were prepared by controlling the composition and sintering temperature of raw materials based on slag from steel refining operations and without the need for a pore-forming agent. Solid-state processing included a phase transformation from low-density raw materials (2.10–2.90 g/cm3) to high-density pyroxene-based ceramics (3.22–3.88 g/cm3). Phase transformations and densification of porous ceramics were investigated by means of mercury intrusion, XRF, SEM and EDS. Results showed that a porous ceramic with optimum properties produced from raw material containing 35 wt.% steel refining slag, exhibited a high water absorption capacity of 31.62%, flexural strength of 18.26 MPa, porosity of 44.5% and an average pore diameter of 1.27 µm. Raw materials with high fineness or content near the pyroxene composition promoted formation of pyroxene and accordingly more volumetric shrinkage which enhanced both bending strength and porosity of the porous ceramics.

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    1. Modelling of Defluidization of ZrO2/Fe Particles in High Temperature Gas Fluidization: Influence of Fe Contents ISIJ International Vol.61(2021), No.7
    2. Opportunity and Challenges of Iron Powders for Metal Injection Molding ISIJ International Vol.61(2021), No.7
    3. Numerical Simulation of Particle Mixing Behavior in High Speed Shear Mixer and Cylinder Mixer ISIJ International Vol.61(2021), No.7

  • Effect of Wettability on Penetration and Flotation Behavior of a Particle in Refining Process

    Akihiro Matsuzawa, Katsuhiro Sasai, Hiroshi Harada, Mitsuhiro Numata

    pp. 2048-2058

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    DOI:10.2355/isijinternational.ISIJINT-2021-056

    Abstract

    Powder blasting is often performed in refining processes for improving their reaction efficiency. Herein, the effect of wettability on penetration and flotation behavior of a particle was examined via a water model experiment. A polypropylene particle was blasted onto the water surface with Ar gas through a single-hole nozzle, and the behavior of the particle during penetration into water to flotation on the water surface was recorded using a high-speed camera. Wettability between the particle and water was changed by applying a repellent or hydrophilic material on the particle. Based on the penetration of the particle, an air column was generated and a residual bubble remained on the particle after the air column ruptured. Repellent particles floated on the water surface in a short period of time because the maximum penetration depth was short and the diameter of the residual bubble was large. Conversely, hydrophilic particles stayed longer in water than repellent particles because the maximum penetration depth was relatively long and the residual bubble detached from the particle. The mechanism which wettability affects penetration and flotation behavior was analyzed, and it was elucidated that the controlling factor of particle behavior is the adhesion point of the air column on the particle. In the case of repellent particles, the adhesion point changes toward to penetrating direction of the particle and the force caused by the surface tension of water increases. Therefore, the maximum penetration depth decreases and the diameter of the residual bubble increases.

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    1. Optimization of Capillary Forces of Clutching Particles in Iron Ore Materials Granulation ISIJ International Vol.61(2021), No.7

  • Numerical Simulation of Particle Mixing Behavior in High Speed Shear Mixer and Cylinder Mixer

    Yang You, Jiabao Guo, Xuewei Lv, Shanshan Wu, Yong Li, Kai Tang, Yaowei Yu

    pp. 2059-2065

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    DOI:10.2355/isijinternational.ISIJINT-2020-768

    Abstract

    The mixing effect of powder materials is crucial in the iron ore granulation process, which determines the composition and particle size distribution, thereby affecting the quality of the sinter. To study the mixing effect of powder particles in a high speed shear mixer (HSSM) and cylinder mixer (CM), numerical simulation based on discrete element method was adopted in this work. For the CM, the particle movement consists of slipping and slumping. For the HSSM, the particle movement consists of rolling and cascading. The particle movement intensity coefficient of the HSSM is larger than that of CM, indicating that the movement of the particles in HSSM is more intensive. For HSSM case with four blades, the variation coefficient of homogeneity increases as rotational speed increases. The number of blades has little effect on the particle movement intensity coefficient and variation coefficient of homogeneity. In comparison to the CM, the variation coefficient of the HSSM reduce the most. It means that the mixing effect of HSSM is better than the CM. These findings are helpful for the improvement of the mixing and granulation efficiency in the iron ore sintering process.

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    1. Viscosity Evaluation of Simulated Foaming Slag via Interfacial Reaction at Room Temperature ISIJ International Vol.61(2021), No.12
    2. Modelling of Defluidization of ZrO2/Fe Particles in High Temperature Gas Fluidization: Influence of Fe Contents ISIJ International Vol.61(2021), No.7
    3. Generation of Pyroxene-Based Porous Ceramics from Steel Refining Slag ISIJ International Vol.61(2021), No.7

  • Optimization of Capillary Forces of Clutching Particles in Iron Ore Materials Granulation

    Krivenko Serhii, Shabelnyk Tetyana

    pp. 2066-2073

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    DOI:10.2355/isijinternational.ISIJINT-2021-032

    Abstract

    Optimization of the operating modes of the pelletizing drum requires the study of the physical processes occurring inside the granules. The purpose of this work is to develop a recommendation for improving the quality of the pelletizing of the charge based on the study of the forces of capillary interaction of particles in granules of granular agglomerate.A deterministic model of capillary adhesion of two particles of arbitrary size and properties based on the calculation of the geometric parameters of the liquid meniscus has been developed. Taking into account the size of the system and to simplify the calculation of the interaction of particles of the sinter batch, the meniscus is represented by a body of revolution with a spherical concave surface.The interaction of 3 mm and 0.1 mm fractions with an average wetting angle θ = 25° for equilibrium states according to the degree of water filling W0.1/3 = W0.1/0.1 and adhesion forces F0.1/3 = F0.1/0.1 was researched. A value of the degree of filling the meniscus Wopt is lower than the optimal values of W for particles with a particle size of R2/R1 = 0.1/0.1 and R2/R1 = 0.1/3, therefore, one should assert not about the optimal degree of filling the meniscus, but about the optimal range of degree filling the meniscus from Wopt = 0.086 to W0.1/3 = 0.21.

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    3. Thermal Stability of Molten Slag in Blast Furnace Hearth ISIJ International Vol.61(2021), No.8

  • Tracking Large-size Inclusions in Al Deoxidated Tinplate Steel in Industrial Practice

    Xiaoao Li, Nan Wang, Min Chen, Tianyou Ma

    pp. 2074-2082

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    DOI:10.2355/isijinternational.ISIJINT-2020-679

    Abstract

    The three-dimensional morphology, size, content and composition of large-size inclusions extracted by large sample electrolysis from RH refining to hot rolling were investigated during the tinplate steel industrial test without calcium treatment. The results showed that the large-size inclusions in the RH refining process are Al2O3 inclusions and incompletely modified CaO·2Al2O3 inclusions, while those in tundish are Al2O3, CaO–Al2O3, CaO–SiO2–Al2O3 and CaO–SiO2–Al2O3–MgO. The typical types of large-size inclusion in slab and hot rolling plates are Al2O3, CaO–Al2O3, SiO2–Al2O3, CaO–SiO2–Al2O3, CaO–SiO2–Al2O3–MgO and CaO–SiO2–Al2O3–TiO2. Secondary oxidation was found to occur in molten steel during the pouring process and protective casting should be improved. Large-size inclusions in hot rolling plates are Al2O3 with a mass fraction of 19.8% and incompletely modified CaO·2Al2O3 inclusions with a mass fraction of 45.9% those have not been completely modified, which have high hardness and are difficult to deform. Therefore, it is recommended that calcium treatment should be carried out at the end of RH refining to reduce the Al2O3 and CaO·2Al2O3 contents. And the effect of calcium addition on the inclusion evolution has been studied by a thermodynamic analysis at 1873 K. With the increase of calcium addition in molten steel, the evolution route of equilibrium precipitations is Al2O3 → CaO·6Al2O3 → CaO·2Al2O3 → CaO·Al2O3 → 3CaO·Al2O3 → 12CaO·7Al2O3 → CaO. The critical calcium content for CaS and CaO formation increases with increasing oxygen content. To avoid the precipitation reaction between [Ca] and [S], the mass fraction of calcium addition needs to be controlled below 0.0040%.

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    2. Numerical Simulation of Particle Mixing Behavior in High Speed Shear Mixer and Cylinder Mixer ISIJ International Vol.61(2021), No.7
    3. CO Desorption and Absorption in Molten Steel: A Review ISIJ International Vol.61(2021), No.5

  • Formation Mechanism of Large-size CaO–Al2O3–MgO–SiO2 Inclusions in High Carbon Chromium Bearing Steel

    Zhiqi Miao, Guoguang Cheng, Shijian Li, Wensheng Qiu, Lingyu Zeng, Hu Long

    pp. 2083-2091

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    DOI:10.2355/isijinternational.ISIJINT-2020-729

    Abstract

    Industrial experiments and thermodynamic analyses were carried out to investigate the formation mechanism of large-size (>30 µm) CaO–Al2O3–MgO–SiO2 (CAMS) inclusions in high carbon chromium bearing steel. It was found that the large-size CAMS inclusions existed during the whole refining process, most of which compositions were located in the liquid region. The average content of SiO2 in CAMS inclusions decreased from 27.5 mass% at argon-blowing station to 3.0 mass% in the hot-rolled bars. The results calculated by Factsage 7.3 indicated that the CAMS inclusions were originated from slag entrapment. During BOF tapping, the low basicity slag with 60 mass% SiO2 was entrapped into steel and combined with the deoxidation product Al2O3, forming a large amount of liquid CAMS inclusions. During LF refining process, [Al], [Ca] and [Mg] in molten steel were affected by the activities of corresponding slag components. The reaction between these three elements and SiO2 in CAMS inclusions originating from slag lead to the decrease of SiO2 in the inclusions. Due to the low interfacial energy between liquid CAMS inclusions and steel, a few large-size inclusions may be inherited to hot-rolled bars. In light of this, several optimization steps were conducted during BOF tapping and argon-blowing station. After the optimization, large-size CAMS originated form BOF tapping were effectively removed.

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  • Evaluation of Thermodynamic Driving Force and Effective Viscosity of Secondary Steelmaking Slags on the Dissolution of Al2O3-Based Inclusions from Liquid Steel

    Pedro Cunha Alves, Vinicius Cardoso Da Rocha, Julio Aníbal Morales Pereira, Wagner Viana Bielefeldt, Antônio Cezar Faria Vilela

    pp. 2092-2099

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    DOI:10.2355/isijinternational.ISIJINT-2021-037

    Abstract

    Dissolution of Al2O3-based inclusions are paramount during production of special steel and slag engineering is key to enhance this phenomenon. This work evaluates the influence of thermodynamic driving force (ΔC) and effective viscosity (ηe) on steel cleanliness of three distinct steel grades and slag composition (Steel/Slag A, Steel/Slag B and Steel/Slag C). Initial and final steel and slag samples were withdrawal on an electric steelmaking facility. The first samples after addition of aluminum as deoxidizer and the second after vacuum degassing stage. X-ray fluorescence and optical spectrometry obtained initial and final samples chemical composition. An ASPEX Explorer acquired inclusions data and FactSage v.7.2 performed thermodynamic calculations. Analysis of steel Al and O content highlighted an inefficient dissolution of Al2O3-based inclusions for Steel/Slag A, deteriorating steel cleanliness. Furthermore, this phenomenon is supported by average inclusions composition on initial and final samples plotted in pseudo-ternary diagram. Steel/Slag B and C provided improved results regarding the dissolution of Al2O3-based inclusions with a final inclusion density below 0.50 mm-2. These two slags composition achieved values of ΔC above 25 and ηe close to 0.10 Pa·s. In addition, their combined effect (ΔC/ηe) presented values above 250 and had the highest linear fit among these analyses. These properties are influenced by slags chemical composition and can be improved controlling parameters as binary basicity and CaO/Al2O3 ratio. Slags B and C were selected to define an optimal range for these parameters, with binary basicity between 3.00–3.50 and CaO/Al2O3 ratio in a range from 2.50–3.50.

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    3. Thermal Stability of Molten Slag in Blast Furnace Hearth ISIJ International Vol.61(2021), No.8

  • End-point Temperature Preset of Molten Steel in the Final Refining Unit Based on an Integration of Deep Neural Network and Multi-process Operation Simulation

    Jianping Yang, Jiangshan Zhang, Weida Guo, Shan Gao, Qing Liu

    pp. 2100-2110

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    DOI:10.2355/isijinternational.ISIJINT-2020-540

    Abstract

    End-point temperature preset of molten steel in the final refining unit is as important as its prediction for casting temperature control. However, it has not been given sufficient concern yet, and the proposed preset models in the literature usually cannot be used as practical tools due to their inherent shortcomings, e.g., oversimplifications made to a real environment during modelling. In this study, a novel preset approach was developed by integrating deep neural network (DNN) and multi-process operation simulation (MOS). By using MOS, the accurate transfer times of heats between the final refining unit and continuous caster can be solved before their actual scheduling, which is very significant for availability of the preset model based on DNN in practice. The DNN preset model was trained and tested with varying the values of hyper-parameters based on vast data points collected from a real steelmaking plant. Furthermore, preset models based on extreme learning machine (ELM) and multivariate polynomial regression (MVPR) were also established for comparison. The testing results indicate the DNN preset model with 3 hidden layers which contain 8, 4 and 2 neurons in sequence shows an advantage over other alternatives because of its evident improvement in preset accuracy and robustness. Meanwhile, a fine classification of data points considering metallurgical expertise can improve the generalization performance of the DNN preset model. The integrated approach has been applying in the studied steelmaking plant, and the ratio of qualified heats increases by 9.5% than before using it.

  • Double Low-rank Based Matrix Decomposition for Surface Defect Segmentation of Steel Sheet

    Shiyang Zhou, Shiqian Wu, Ketao Cui, Huaiguang Liu

    pp. 2111-2121

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    DOI:10.2355/isijinternational.ISIJINT-2021-024

    Abstract

    Despite advances in surface defect segmentation of steel sheet, it is still far from meeting the needs of real-world applications due to some method usually lack of adaptiveness to different shape, size, location and texture of defect object. Based on the assumption that each defect image is composed of defect-free background components that reflect the similarities of different regions and defect foreground components that reflect unique object information, we formulate the segmentation task as an image decomposition problem. To this end, we develop a double low-rank based matrix factorization framework for decomposing the surface defect image into defect foreground image and defect-free background image. Furthermore, considering the similarity of the defect-free background sub-regions and the defective sub-regions, Laplacian and sparse regularization terms are introduced into the matrix decomposition framework to improve their representation ability and discriminative ability. Importantly, the proposed method is unsupervised and training-free, so it does not requiring a large number of training samples with time-consuming manual labels. Experimental results on synthetic and real-world surface defect images show that the proposed method outperforms some state-of-the-art approaches in terms of both subjective and objective experiments.

  • Multicomponent Internal Standard Methods for Determination of Vanadium, Chromium, Nickel, and Copper in Tool Steel Samples in Continuum-light-source Flame Atomic Absorption Spectrometry

    Kenichi Nakayama, Kazuaki Wagatsuma

    pp. 2122-2126

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    DOI:10.2355/isijinternational.ISIJINT-2020-732

    Abstract

    This paper suggests an improved method for the sample preparation to quantify vanadium, chromium, nickel and copper in tool steel and high-speed steel by using flame atomic absorption spectrometry. The suggested method prepared two specimen solutions containing different internal standard elements: one included nickel for the quantifications of vanadium or copper and cobalt for the quantification of chromium and another included cobalt and phosphoric acid for the quantification of nickel, after the sample was digested with an acid mixture of hydrofluoric acid, nitric acid and phosphoric acid by using a microwave oven. A multi-wavelength high-resolution spectrometer system was employed to be simultaneously measured absorption lines for several pairs of an analyte and an internal standard element, such as vanadium and nickel, chromium and cobalt, nickel and iron, cobalt and phosphorus oxide, and copper and nickel. The internal standards contributed to more accurate and precise quantification of vanadium, chromium, nickel, and copper in tool steel and high-speed steel samples.

  • Characteristics of High Speed Steel/ductile Cast Iron Composite Roll Manufactured by Electroslag Remelting Cladding

    Yulong Cao, Yanwu Dong, Zhouhua Jiang, Guangqiang Li, Zhengrong Zhao

    pp. 2127-2134

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    DOI:10.2355/isijinternational.ISIJINT-2020-594

    Abstract

    In the present study, high-speed steel (HSS)/ductile cast iron (DCI) composite roll was manufactured by the electroslag remelting cladding (ESRC) technology. The compositional variation, grain size, microstructure, hardness, and tensile strength of the HSS layer and the bimetallic interface were investigated systematically. The obtained results illustrated that the chemical composition of the cladding layer (HSS) changed dramatically due to the surface melting of the roll core (DCI) and the mechanical mixing of the bimetallic liquids. The different solidification rates and chemical compositions in different regions of the HSS layer led to great variations of the grain size, the carbide content, and the hardness. In addition, a bimetallic transition zone (about 9.47 mm) was generated between the HSS layer and the DCI core due to the elemental migration and diffusion between the bimetals. Carbides of different types, morphologies, sizes, and compositions had direct influences on interfacial properties.

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  • Online Cooling System and Improved Similar Self-adaptive Strategy for Hot-rolled Seamless Steel Tube

    Dong Chen, Rui Zhang, Yunjie Li, Zhenlei Li, Guo Yuan

    pp. 2135-2142

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    DOI:10.2355/isijinternational.ISIJINT2021-013

    Abstract

    In conventional hot-rolled seamless steel tube production, the tube was air cooled to room temperature, and the enhancing of mechanical properties mainly depends on adding alloys elements and additional offline heat treatment. Control cooling was an effective method that can obviously enhance mechanical properties and widely used in hot-rolled strip and plate production lines. To realize control cooling process, an online control cooling equipment was introduced, which can implement the efficient and uniform cooling process for annular seamless tube. Meanwhile, the controller system was built to ensure online continuous cooling process quickly and stably. In order to guarantee precise temperature control, a temperature model based on energy balance and finite difference method was proposed. In addition, a self-adaptive strategy based on improved similar tube was obtained for temperature control, which builds the self-adaptive model combining constrained one pass clustering algorithm and kNN algorithm. Finally, the proposed online control cooling system and temperature model were applied in a PQF460 hot-rolled seamless steel tube production line, which greatly improved qualification rate whilst retaining a good control precision and stability.

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  • Parameter Optimization of Thermal Shrinkage Technique for Simple Numerical Simulation of Welding Angular Distortion

    Hiroki Murakami, Katsumasa Miyazaki, Kenji Honnami, Shigetaka Okano, Masahito Mochizuki

    pp. 2143-2149

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    DOI:10.2355/isijinternational.ISIJINT-2020-706

    Abstract

    The thermal shrinkage technique, which uses shrinkage strain to determine weld distortion, shows promise as a simple simulation for predicting the weld distortion of large welded structures. To date, there has not been adequate research on how to set input data based on welding conditions. In this work, we perform a parametric study using thermal shrinkage technique in which we vary the input data to investigate the optimum setting method. To compare angular distortion obtained by the thermal shrinkage technique, Metal active gas welding was conducted under five welding conditions and thermal elastic-plastic analysis was conducted under the same welding condition. Under all five conditions, the angular distortion obtained by the thermal shrinkage technique accurately reproduced that obtained by experiments and by thermal elastic-plastic analysis. We found that the optimum input data settings were the shrinkage strain of −0.012 and a shrinkage zone in which the maximum temperature reached 500°C or more. From the results, the similarity and the difference between the characteristics of angular distortion in the thermal shrinkage technique and that in the thermal elastic-plastic analysis was discussed based on the inherent strain and the moment. Moreover, the way in which inherent strain based on the both-ends-fixed-bar analogy occurred can explain the agreement in angular distortion in the case of the optimum input data settings. Our results demonstrate that a suitable setting method of input data has been established.

  • Friction Stir Welding of High Phosphorus Weathering Steel —Weldabilities, Microstructural Evolution and Mechanical Properties

    Takumi Kawakubo, Tomoya Nagira, Kohsaku Ushioda, Hidetoshi Fujii

    pp. 2150-2158

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    DOI:10.2355/isijinternational.ISIJINT-2021-007

    Abstract

    Phosphorus (P) addition is expected to simultaneously increase the strength and corrosion resistance of weathering steels. However, P causes solidification cracking in the fusion welding process and reduces the toughness of the steel. To avoid these problems, the P content of weldable SMA490AW weathering steel is currently limited to below 0.035 mass%. High P steels which are impossible to be joined by the fusion welding process, can be joined by a solid-state joining process, i.e., friction stir welding (FSW). Because the stir zone obtained by FSW contained very fine grains, its toughness was expected to improve. This study applies FSW to high-P weathering steels and examines the weldability of the product. The microstructural evolution and mechanical properties of the stir zone were investigated at different welding temperatures. The macroscopic cross-sectional observations of the FSW joints revealed crack-free structures even in steel containing 0.3 mass% P. Moreover, FSW significantly refined the grain structure in the stir zone. Consequently, the ductile-to-brittle transition temperature of the stir zone was approximately 150°C lower in the steel containing 0.3 mass% P and welded below A1 (average grain size = 2.5 µm) than in the base material (average grain size = 23 µm). It appears that the grain refinement by FSW overcomes the embrittlement caused by excessive P content.

  • Effects of Excess C on New Grain Formation and Static Recrystallization Behavior at Shear Bands in Cold-Rolled Ultra-Low Carbon Steel Sheets

    Hidekazu Minami, Yoshimasa Funakawa, Tomoki Tsuji, Masakazu Kobayashi, Hiromi Miura

    pp. 2159-2166

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    DOI:10.2355/isijinternational.ISIJINT-2020-727

    Abstract

    The effects of excess carbon on static recrystallization of cold-rolled steel sheets were studied using Ti-bearing ultra-low carbon steels with and without carbon in solution. Here, excess carbon means solute carbon added beyond the atomic equivalent ratio with Ti. Static recrystallization was evidently accelerated by the presence of excess carbon. Microstructural observation confirmed that statically recrystallized grains were generated at ferrite grain boundaries and deformation bands. Preexisting fine grains also stimulated static recrystallization. However, nucleation at deformation bands was not particularly significant in Ti-bearing ultra-low carbon steels without excess carbon. This difference derived from excess carbon is discussed in detail in relation to stored energy, preferential nucleation sites of static recrystallization and grain boundary migration.

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  • Brittle-to-ductile Transition in Martensite – Bainite Steel

    Takumi Sakamaki, Masaki Tanaka, Tatsuya Morikawa, Hidenori Nako, Shigenobu Nanba

    pp. 2167-2175

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    DOI:10.2355/isijinternational.ISIJINT-2020-757

    Abstract

    To understand the effect of composite structure on brittle-to-ductile transition (BDT) in low-carbon martensite–bainite steel, this study investigates the temperature dependence of the impact absorbed energy in five types of steel having the same chemical composition: fully martensitic steel, fully bainitic steel, and martensite–bainite steel with bainite fractions of 4%, 15%, and 55%, respectively. The BDT temperature was the highest for fully martensitic steel, followed by those of the martensite–4% bainite, martensite–15% bainite, martensite–55% bainite, and full bainitic steel. The BDT temperatures of martensite–15% bainite, martensite–55% bainite, and fully bainitic steel were close despite the large differences in their bainite volume fractions, suggesting that the trend of BDT temperatures cannot be explained simply based on the rule of mixture. The temperature dependence of 0.2% proof stress was measured in each steel to understand the trend of BDT temperature based on the shielding theory. Optical micrographs and the temperature dependence of effective stress indicated that the dislocations in bainite were preferentially activated and governed the yielding and BDT in the martensite-barite steels. This phenomenon was also linked to the network structures of bainite surrounding the martensite, where bainite was subjected to plastic deformation immediately after yielding in the employed steel.

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  • Production Years of Iron of Old Japanese Nails of Amanosan-Kongo-ji and Kasugataisha Shrine Calibrated from 14C Age

    Kazuhiro Nagata, Yasuko Furunushi

    pp. 2176-2180

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    DOI:10.2355/isijinternational.ISIJINT-2021-095

    Abstract

    The production age of iron of old Japanese nails used at the eaves of the Kondo (main hole) of the Amanosan-Kongo-ji temple and the corridor of the Kasugataisha shrine was measured by the 14C age method. The 14C concentration of charcoal absorbed by iron during ironmaking is the value at the time of logging, and it was taken into consideration that the trees were logged between 20 and 25 years old. By referring to the history and repair records of each temple and shrine, it was found that iron for the nails at the Kongo-ji temple and the Kasugataisha shrine was produced between 1150–1155 and 1555–1560, respectively. These values were compared with the production year of iron of the old Japanese nails at the Daibutsuden in the Todai-ji temple, the Kuri in the Kyoto Manshuin temple and the Zaodo in the Yoshino-Kinpusen-ji temple in the previous report.1) It was found that the iron production years of the nails at the Kasugataisha shrine and the Kinpusen-ji temple were the same, and there was a difference of 80 years in the production years between the two nails at the Kinpusen-ji temple.

  • Oxidative Quaternary Acidic Mixture on Microwave-assisted Digestion for High-Carbon Iron Samples

    Kenichi Nakayama, Kazuaki Wagatsuma

    pp. 2181-2184

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    DOI:10.2355/isijinternational.ISIJINT-2020-716

    Abstract

    This paper suggested an improved method for the sample preparation of pig iron and cast iron in inductively coupled plasma atomic emission spectrometry. Conventional digestion methods using a mixture of hydrochloric acid and nitric acid, associated with fuming with phosphoric and sulfuric acids or fuming with perchloric acid, have a poor-ability to decompose the iron sample completely. Alternatively, a microwave digestion method using an acidic mixture of hydrofluoric acid, nitric acid, phosphoric acid, and potassium chlorate, enabled various iron samples to be fully decomposed. The suggested procedure was applicable to quantify titanium, vanadium, chromium, manganese, nickel, copper, and molybdenum in high-carbon iron samples using a similar dissolution method.
  • © 2021 The Iron and Steel Institute of Japan

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