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ISIJ International Vol. 60 (2020), No. 11

ISIJ International
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Grid List Abstracts
オンライン版ISSN: 1347-5460
冊子版ISSN: 0915-1559
発行機関: The Iron and Steel Institute of Japan

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キーワードランキング

26 Dec. (Last 30 Days)

ISIJ International Vol. 60 (2020), No. 11

Solid-liquid Interfacial Energy for Fe–Cr Alloy under Temperature Gradient from Molecular Dynamics Simulation

Kensho Ueno, Yasushi Shibuta

pp. 2301-2305

DOI:

10.2355/isijinternational.ISIJINT-2019-769

抄録

The solid-liquid interfacial energy of Fe–Cr alloy under temperature gradient is investigated by molecular dynamics (MD) simulations in conjunction with a capillary fluctuation method including the effect of temperature gradient. It is revealed from the MD simulation that fluctuation of the solid-liquid interface decreases with increasing temperature gradient. This results in a large value of the solid-liquid interfacial energy under large temperature gradient. On the other hand, there is a competing effect reducing the solid-liquid interfacial energy with increasing temperature gradient in the formulation of the capillary fluctuation method including the effect of temperature gradient. As a result, the solid-liquid interfacial energy doesn’t change significantly at small temperature gradient. Moreover, it is confirmed that the solid-liquid interfacial energy of Fe–Cr alloy decreases with increasing Cr composition at Fe-rich composition regardless of the temperature gradient.

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Surface Tension Calculation of Molten Slag in SiO2–Al2O3–CaO–MgO–‘FeO’–‘Fe2O3’ Systems Based on a Statistical Modelling Approach

Jianjiang Xin, Nan Wang, Min Chen

pp. 2306-2315

DOI:

10.2355/isijinternational.ISIJINT-2019-807

抄録

A calculation model for surface tension of molten slags in SiO2–Al2O3–CaO–MgO systems, based on a statistical modelling approach, was further extended to SiO2–Al2O3–CaO–MgO–‘FeO’–‘Fe2O3’ multi-component systems. A total number of 1493 surface tension data reported in literatures, including 661 iron-containing data in this study, have been collected and critically reviewed for optimizing model parameters. The model achieves an excellent agreement with literature values for iron -containing melts with an average error of 4.9% and overall absolute error of 29.75 mN/m. Moreover, the dependence of surface tension on composition and temperature the composition has been discussed using the present model. The results show that the surface tension always obviously decrease with the increment of SiO2 content and substitution of CaO or Al2O3 by MgO will cause a decrease in the surface tension. In case of silica-free ternary systems such as the Al2O3–CaO–‘Fe2O3’ and CaO–MgO–‘Fe2O3’, the surface tension decreases with increasing ‘Fe2O3’ concentration with constant Al2O3 and CaO level respectively, indicating the network former role of ‘Fe2O3’ in these studied systems. Temperature coefficient is closely related with the melt composition and positive values for high ‘FeO’ and ‘Fe2O3’ contents in the melts were found.

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Effect of Steel-refractory Reactions on Removal of Arsenic from Molten Steel with Lanthanum Additions

Hongpo Wang, Silu Jiang, Peng Yu, Lifeng Sun, Yu Wang

pp. 2316-2324

DOI:

10.2355/isijinternational.ISIJINT-2020-052

抄録

To formulate strategies to remove arsenic from molten steel by adding rare earth elements (REs), the evolution of inclusions in steel with different lanthanum additions was studied, and the effect of reactions between lanthanum and magnesium crucibles on the removal of arsenic was discussed. The results show that the addition of lanthanum can remove arsenic from molten steel, but steel-refractory reactions dramatically influenced the removal effect. The arsenic removal was determined by the generation of La–S–As. The reactions between lanthanum and magnesia crucibles partly consumed lanthanum and decreased its effective concentration acting on arsenic. Further, the reaction product dissolved magnesium consumed a part of sulfur that was disadvantageous for the formation of La–S–As. Besides, a sequence of reactions existed after the addition of lanthanum. The original Si–Mn–Al–O inclusions were changed to lanthanum-containing oxides first and then to MgO-rich oxides. The reaction to generate La–S–As mainly took place within 5 min. The consumption of REs by crucible refractories is an important issue that needs consideration. Alumina crucibles are more favored over magnesia crucibles when using REs to remove arsenic from molten steel.

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Pre-reduction Behaviour of Manganese Ores in H2 and CO Containing Gases

Didier Ngoy, Dmitry Sukhomlinov, Merete Tangstad

pp. 2325-2331

DOI:

10.2355/isijinternational.ISIJINT-2020-120

抄録

This paper presents results of a study conducted on the pre-reduction of Assmang and Comilog ores with gases of CO+CO2 and CO+H2+CO2 up to 1000°C. Non-isothermal experiments were carried out in a vertical thermogravimetric tube furnace. Four different gas mixtures were considered. That is, gas mixtures of 50%CO/50%CO2, 41%CO/18%H2/41%CO2 and gas mixtures of 70%CO/30%CO2, 41%CO/41%H2/18%CO2 whose CO/CO2 ratio is respectively of 1/1 and 2.3/1. The ore and reduced samples were characterized by X-ray fluorescence technique followed by a scanning electron microscopy analysis. The extent of reduction was considered based on the recorded weight loss together with the chemical analyses done on the processed samples. It was found that for the same oxygen pressure, the highest reduction rate was achieved when hydrogen was present in the gas mixture. Results also showed that when the oxygen pressure of the gas mixture was lower, the reduction rate was the highest as expected.

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Effect of Sulfur in Slag on Dynamic Change Behavior of Liquid Iron/Molten Slag Interfacial Tension

Masanori Suzuki, Masashi Nakamoto, Toshihiro Tanaka, Yuichi Tsukaguchi, Kazuaki Mishima, Masahito Hanao

pp. 2332-2338

DOI:

10.2355/isijinternational.ISIJINT-2020-144

抄録

In continuous casting process of steel, the slag entrapment into liquid steel should be minimized by controlling the interfacial tension between liquid steel and molten slag. However, the liquid iron/molten slag interfacial tension dynamically changes when redox chemical reaction occurs at the iron/slag interface. This dynamic change behavior of the interfacial tension could be explained by assuming excess adsorption of oxygen atoms made by the decomposing reaction of slag components and its desorption at the iron/slag interface. In this study, we investigate the effect of sulfur in slag on the dynamic change of the liquid iron/molten slag interfacial tension, where sulfur initially exists in slag but not in iron. We evaluate apparent contact angle at the gas/molten slag/liquid iron triple interface in the floating lens method, which is determined by the balances among surface tension of iron, surface tension of slag and interfacial tension between iron and slag in both horizontal and vertical directions. When a silicate slag droplet contacted with liquid iron surface, the apparent contact angle rapidly decreased, reached the minimum and then gradually increased to achieve the steady value. The 0.1 mass% sulfur addition in the slag further decreased the contact angle at the minimum. It was indicated that sulfur as well as oxygen in the slag are simultaneously adsorbed at the iron/slag interface to dynamically decrease the interfacial tension.

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Chemical Thermodynamic Insights on Rare-Earth Magnet Sludge Recycling

Mary-Elizabeth Wagner, Antoine Allanore

pp. 2339-2349

DOI:

10.2355/isijinternational.ISIJINT-2020-320

抄録

Recycling rare-earth magnets poses a metallurgical challenge due to their high reactivity and the difficulty in separating individual rare-earth elements. These challenges are compounded when considering magnet machining sludge, which is more heavily oxidized and contains more contaminants than typical end-of-life magnets. If recycled, these materials are sent back to the primary smelter, where they are separated and purified to make new feedstocks which are often re-mixed into a new magnet. Here, a thermodynamic study is presented, assessing the oxidation behavior of rare-earth magnets. The theoretical minimum energy to reduce the whole magnet sludge, without separation and purification, is also presented. A comprehensive model including 25 elements is provided, using a hybrid CALPHAD-classical method. Oxygen distribution in a rare-earth magnet, with a total O content ranging between 0.09% to 5.4 wt%, is assessed. The results predict a final distribution of 40 wt% rare-earth in the oxide phase, with 60 wt% still remaining in the metallic phase. The model performance with respect to published experimental data is used to shed light into the possible processing methods for recycling.

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Effect of Titanomagnetite Ironsand Coal Composite Hot Briquette on Softening-melting Performance of Mixed Burden under Simulated Blast Furnace Conditions

Jue Tang, Zedong Zhang, Mansheng Chu, Wei Zhao, Zhenggen Liu

pp. 2350-2356

DOI:

10.2355/isijinternational.ISIJINT-2020-098

抄録

Titanomagnetite ironsand coal composite hot briquette (ICHB) was proposed as a novel type of burden to enhance the incremental and high-efficiency utilization of ironsand in blast furnace. ICHB was prepared firstly under laboratory conditions, with a compressive strength higher than 3000 N. Then the national charging ratio of ICHB in the mixed burdens was explored to conduct softening-melting experiments with the simulated BF conditions. Finally the softening-melting-dripping mechanism of mixed burdens was discussed by thermodynamic calculations, SEM-EDS, and XRD detections in this work. It was showed that the softening-melting-dripping behavior and the permeability of mixed burdens could be improved obviously by an appropriate ICHB charging. With the increasing of ICHB charging ratio, the location of cohesive zone was shifted down gradually and its thickness was the narrowest at the ICHB charging ratio of 10%, which was beneficial to BF smelting. Meanwhile, the dripping ratio of mixed burden also achieved the maximum value of 66.71% when the ICHB charging ratio was 10%. However, the excessive ICHB charging would promote the precipitation of Ti(C,N) with a high melting point at the interface between metal and slag, which resulted in the deterioration of dripping and further worsening the gas permeability of mixed burdens. Comprehensively considering the softening-melting-dripping behavior and the permeability of mixed burden, and the precipitation of Ti(C,N), the recommended ICHB charging ratio was 10%.

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Phase Composition and Formation Mechanism of Slag Crust in Blast Furnace

Hengbao Ma, Kexin Jiao, Jianliang Zhang, Lei Zhang, Xiaoyue Fan

pp. 2357-2365

DOI:

10.2355/isijinternational.ISIJINT-2020-113

抄録

Copper stave damage is common problem in blast furnace operations, and the formation of slag crust is beneficial to reduce the damage of copper stave. Therefore, an in-depth understanding of phase composition and formation mechanism of slag crust is helpful to clarify the protection mechanism of copper stave, so as to control the growth of the slag crust and to increase the service life of copper staves. In this study, the slag crust from a copper stave blast furnace was sampled, and the phase composition and structure of the slag crust were characterized in detail through XRD analysis and SEM-EDS. The results indicated that the slag crust presented apparent layer structure as the solid slag layer and viscous layer, which primarily consisted of gehlenite (Ca2Al2SiO7), calcium aluminate (CaAl4O7), magnesia-alumina spinel (MgAl2O4), pleonaste (Mg0.7Fe0.23Al1.97O4), kaliophilite (KAlSiO4) and metallic iron. In addition, the ternary phase diagram analysis of CaO–SiO2–Al2O3 showed that the primary crystal phase of the slag is in the gehlenite region, and that the primary crystal region migrates to the calcium aluminate region with the increasing of Al2O3 content, which are beneficial to the slag crust formation. Finally, the formation mechanism of slag crust was proposed.

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Reaction Behaviors of Various Agglomerates in Reducing the Temperature of the Thermal Reserve Zone of the Blast Furnace

Kenichi Higuchi, Kazuya Kunitomo, Seiji Nomura

pp. 2366-2375

DOI:

10.2355/isijinternational.ISIJINT-2020-115

抄録

As an innovative measure to mitigating CO2 emissions during ironmaking, the enhancement of carbon reactivity in blast furnaces is promising. It can reduce the temperature of the thermal reserve zone (TRZ), which is among the limiting factors to reaction efficiency in blast furnaces, thereby enabling operation under a low reducing agent rate (RAR). Therefore, reaction behaviors of two types of agglomerates with high carbon reactivity, composite agglomerates (CAs), and Ferro-coke, were evaluated using a softening-melting tester and via large-scale thermogravimetry. Process estimation of the blast furnace using them was also performed using a counter-current reaction simulator. CAs exhibited low-temperature gasification, efficiently promoting reduction by mixing with sintered ores. The carbon-consumption ratios of CAs and Ferro-coke were higher than that of coke. The reactive coke agglomerate, which is reinforced CAs with high carbon content toward reducing the RAR, exhibited the highest carbon reactivity, because of the coupling phenomena between the gas reduction of iron oxide and gasification of carbon. The addition of metallic iron to the CA increased the consumption of carbon and reduction of sintered ores, because of the catalytic effect. A combined use of the CA and Ferro-coke in the blast furnace successfully reduced the temperature of the TRZ by 150°C, offering the potential to decrease RAR by 35 kg/t-HM. Estimation of the distance between carbon and iron oxide or metallic iron in these agglomerates revealed that reducing the temperature of the TRZ by them was closely associated with shortening the distance.

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Granulation Behavior of an Iron Ore Sintering Mixture Containing High Grade Pellet Feed with Different Specific Surface

Vinícius de Morais Oliveira, Alei Leite Alcantara Domingues, Mauricio Covcevich Bagatini, Valdirene Gonzaga de Resende

pp. 2376-2384

DOI:

10.2355/isijinternational.ISIJINT-2020-023

抄録

High-grade iron ores became more attractive due to the searching for lower slag rate operation in blast furnaces aiming to reduce CO2 emissions as the environmental regulation became even more restricted. The granulation behavior of high-grade ores individually and together with other iron ores played an important role for sintering process. In this context, this work aims to evaluate the granulation behavior of a pellet feed with different specific surfaces. To carry out this study, 25% of pellet feed was added to an iron ore mix in a bench scale drum. The Granulation Index (GI) was determined and samples were collected after granulation step for quasi-particles investigation. The results showed that a previous mechanical treatment of the pellet feed by roller press is suitable in order to enable a good granulation behavior of this fine material, which was essential to guarantee its use as raw material in sintering process. The fraction below 0.045 mm of the pressed pellet feed helped to improve the granulation of the natural pellet feed. The thickness of the adherent layer and means size of quasi-particles increased with the specific surface. The GI results increase with the pellet feed specific surface, up to 1400–1500 cm2/g stabilizing around 86–90%. The fines below 0.15 mm that remained agglomerated, after drop test, had similar behavior of GI. Finally, it was possible to obtain a minimum specific surface level (1400–1500 cm2/g) to achieve an optimum performance in the granulation step which may promote a good sintering process permeability conditions.

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Dissection Investigation of Forming Process of Titanium Compounds Layer in the Blast Furnace Hearth

Kai Gao, Kexin Jiao, Jianliang Zhang, Lei Zhang, Cui Wang, Weimin Gong, Jingxian Zheng, Haibin Zhang

pp. 2385-2391

DOI:

10.2355/isijinternational.ISIJINT-2020-146

抄録

In this paper, titanium compounds samples were obtained by dissecting the blast furnace for which protected the hearth by adding titanium ores for a long time, and the formation process of the titanium protective layer in the blast furnace was deduced. It was found that Ti(C, N) precipitated in the molten iron initially, and then grew up in the slag by grain boundary migration between grains. Finally, Ti(C, N) grains consolidated with slag and iron to form a protective layer. Furthermore, the 3D morphology of the precipitated phase of Ti(C, N) was also observed by the acid attack method, found that the Ti(C, N) grains mainly in the form of the layered structure and stepped rectangular structure. Besides, the internal of the Ti(C, N) grains was not dense packing. The above results can provide an in-depth understanding of furnace protection with titanium ores.

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Reaction Behaviors of Mixed Burdens Consisting of Pellets and Sintered Ores in an Experimental Blast Furnace

Kenichi Higuchi, Tsunehisa Nishimura, Tetsuya Shioda, Mikael Pettersson, Peter Sikström

pp. 2392-2399

DOI:

10.2355/isijinternational.ISIJINT-2020-194

抄録

Low-MgO sintered ores have developed into dominant burden materials for large blast furnaces operating under high pulverized coal injection in Japan, because of their low gangue content and high strength. Mixing MgO-bearing burdens with low-MgO sintered ores is an effective approach to satisfy the MgO requirement of blast furnaces. Therefore, a basket-evaluation test was performed in an experimental blast furnace (EBF) to investigate the reduction behavior of olivine pellets mixed with low-MgO sintered ores. The reduction behavior with lime-fluxed pellets was also evaluated as a reference. Softening-melting tests were also conducted under the same mixing conditions as those in the EBF tests. Olivine pellets exhibited smaller pores and contained finer hematite grains before reduction. These microstructural features influenced their reduction behavior, with low size disintegration observed in the lumpy zone in the EBF. Numerous cohesive masses with slag formed at the interface between sintered ores and lime-fluxed pellets in the EBF, facilitating their melting. In contrast, a small amount of slag was found at the interface between sintered ores and olivine pellets. The results of the softening-melting tests also revealed the superiority of olivine pellets during melting. Despite the low temperature of the initial melt formation during reduction, olivine pellets exhibited lower liquid ratios at high temperatures, resulting in a decrease in exuded slag when mixed with low-MgO sintered ores. This work proposes a general mechanism for the melting behaviors of mixed burden materials for blast furnaces.

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Comprehensive Technologies for Iron Ore Sintering with a Bed Height of 1000 mm to Improve Sinter Quality, Enhance Productivity and Reduce Fuel Consumption

Zhengjian Liu, Lele Niu, Shijun Zhang, Guanqiu Dong, Yaozu Wang, Guilin Wang, Jian Kang, Longzhi Chen, Jianliang Zhang

pp. 2400-2407

DOI:

10.2355/isijinternational.ISIJINT-2020-219

抄録

Despite its many advantages, the materials layer with thickness exceeding 900 mm hinders further development of thick bed sintering. In order to break through the bottleneck of ultra-thick bed sintering, University of Science and Technology Beijing and Tiangang United Special Steel initiated a cooperation. Firstly, by analyzing the characteristics of the ultra-thick bed sintering, this study aims to make high air permeability and low air leakage rate the focus technically. Then a “triple sync” theory including the liquid phase front, heat transfer front and flame front and the concept of “Full Active Lime Intensified Sintering” were proposed to support thick bed sintering. On this basis, Tiangang United Special Steel develops a series of comprehensive technologies including raw materials controls, granulation enhancements and air leakage improvements, then efficient and stable sintering production with a bed height of 1000 mm in their two 260 m2 sintering machines is achieved. After the implementation of these technologies, the productivity reaches 1.89 t/(m2·h), the solid fuel consumption was only 41.85 kg/t, meanwhile the tumbler, reduction, and low-temperature reduction degradation index RDI+3.15 of produced sinter are 78.24%, 87.17%, and 74.2%, respectively. While promoting the development of ultra-thick bed sintering, it has also brought significant economic and environmental benefits.

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Influence of Basicity on the Viscosity and Crystallization Characteristics of Chromium-containing High-titanium Slag

Jing Ma, Wei Li, Guiqin Fu, Miaoyong Zhu

pp. 2408-2415

DOI:

10.2355/isijinternational.ISIJINT-2020-244

抄録

In this paper, the influence of basicity (CaO/SiO2) on the viscosity and crystallization characteristics of chromium-containing high-titanium slag was studied. The melting temperature and viscosity were measured by employing the hemisphere and rotating cylinder methods, and the composition and morphology of the crystallized phase were analyzed by X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy. The results showed that the crystallization sequence during the cooling process was spinel, followed by anosovite. The increased basicity led to enhanced softening, hemispherical, and flowing temperatures of chromium-containing high-titanium slag; however, the viscosity significantly decreased. The basicity obviously affected the crystallized phase composition. Furthermore, anosovite was the dominant crystallized phase and a proper level of basicity was beneficial for titanium enrichment.

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A General Model for Solutes Activity Interaction Parameters in Dilute Metallic Solutions

Tianhua Ju, Xueyong Ding, Long Zhang, Weiliang Chen, Bo Wang, Xinlin Yan

pp. 2416-2424

DOI:

10.2355/isijinternational.ISIJINT-2019-564

抄録

Several models had been proposed to estimate the activity interaction parameters in a dilute metallic solution from the physical parameters of constituent elements. However, these models either need to choose an asymmetric component or do not satisfy by themselves the basic requirement of the reciprocal relation, i.e., εij = εji. As a result, their practical applications are greatly limited. In this paper, a general model, which doesn’t need to choose an asymmetric component but satisfies the basic requirement of the reciprocal relation, is introduced. The applicability of the new model is tested in ferrous alloy systems and non-ferroalloy systems. The results are better than those from the previous model with less deviations from experimental data.

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Crystallization Control for Fluorine-free Mold Fluxes: Effect of Na2O Content on Non-isothermal Melt Crystallization Kinetics

Qifeng Shu, Jeferson Leandro Klug, Samuel Lucas Santos Medeiros, Nestor C. Heck, Yang Liu

pp. 2425-2435

DOI:

10.2355/isijinternational.ISIJINT-2020-132

抄録

There are increasing demands for developing fluorine-free mold fluxes for continuous casting of steel. When removing fluorine from mold flux composition, it is necessary to replace it with oxides, which must maintain the technological parameters, related to viscosity, melting characteristics, and crystallization behavior. For industrial developments in the CaO–SiO2–Na2O–Al2O3–TiO2–B2O3–MgO (with basicity = 1, Al2O3 = 7%, TiO2 = 5%, B2O3 = 3%, MgO = 2%) slag system, it is necessary to know the effect of Na2O concentration regarding crystallization kinetics. This is especially important for fluorine-free mold fluxes for peritectic steel slab casting. In this work, the crystals´ precipitation sequence for this system during cooling was determined, combining Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The Friedman differential isoconversional method was applied for determining the effective activation energy for non-isothermal crystallization, since it gives relevant information without knowing the form of the kinetic equation. A modified Avrami model was used to calculate the n values; it was found that they are near 2.5, for all analyzed samples, which means that it is related to the crystallization mode diffusion controlled, with constant nucleation rate and three-dimensional growth. This agrees with the SEM micrographs, where dendritic structure is observed for all crystalline samples. Additionally, structural information got from Raman spectroscopy, for the samples in vitreous state, was used to interpret crystallization tendency, i.e., the fact that crystallization was enhanced by increasing Na2O content, due to slag depolymerization. Moreover, computational thermodynamics was used to analyze mold fluxes crystallization behavior.

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In situ Phase Analysis during Self-sintering of BOS Filter Cake for Improved Recycling

Raymond James Longbottom, Brian Joseph Monaghan, David John Pinson, Nathan Alan Stewart Webster, Sheng Jason Chew

pp. 2436-2445

DOI:

10.2355/isijinternational.ISIJINT-2020-142

抄録

The self-sintering of basic oxygen steelmaking (BOS) filter cake has been studied using in situ high temperature X-ray diffraction (XRD) during heating in air from room temperature to 1273 K. The aim of the study was to improve the understanding of the self-sintering process, using this in situ method to identify what reactions occur at different temperature ranges.The in situ phase analysis measurements correspond well, and are consistent with, the previously reported characteristics of BOS filter cake oxidation. However, the in situ measurements have allowed a more detailed analysis of the reactions taking place over the temperature ranges studied. Wüstite was the first component of the BOS filter cake to react with air, reacting at temperatures of approximately 373 K to 773 K to form a magnetite-zinc ferrite spinel solid solution. The reaction of metallic iron began at higher temperatures than wüstite, beginning at ~633 K and finishing at ~873 K. The decomposition of fluxes (mainly CaCO3) occurred at temperatures above 873 K. At temperatures higher still, at approximately 1073 K, hematite reacted with zinc oxide to form zinc ferrite.The knowledge that wüstite reacts at the lowest temperatures is an improvement in the understanding of the self-sintering of BOS filter cake, and may give insights into the initiation of the self-sintering process. This improved understanding will aid analysis and approaches focused on process optimisation to increase the amount of filter cake that can be recycled back to the BOS.

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Inclusion Characteristic in Tinplate Steel in RH Refining and Kinetics Limitation of Calcium Transfer by Refining Slag

Xiaoao Li, Nan Wang, Min Chen, Ruiqi Zeng

pp. 2446-2454

DOI:

10.2355/isijinternational.ISIJINT-2020-237

抄録

The characteristics of inclusions including composition, morphology, number, and size in tinplate steel were studied by industrial experiments and thermodynamic calculations during the RH refining process. The results indicated that two types of Al2O3 inclusions including cluster and single-particle are generated at first after Al addition. With the slag-metal and refractory-metal reactions, Al2O3 inclusions, CaO·Al2O3 inclusions, MgO·Al2O3 spinel inclusions, and CaO–MgO–Al2O3 ternary system inclusions are found in the middle of RH refining. Only single-particle Al2O3, CaO·Al2O3 inclusions with high melting point, and CaO–MgO–Al2O3 ternary system inclusions are found at the end of RH refining. From Al addition to the end of RH refining, the total number of inclusions showed a decreasing trend and the proportion of the number density decreased by 70%. About 62% of inclusions are smaller than 10 µm at the end of RH refining, which are difficult to be removed from the liquid steel. The mass transfer of Ca from the refining slag to the liquid steel has a significant effect on the content of [Ca] in liquid steel. Al2O3 inclusions generated in liquid steel can only be modified to CaO·Al2O3 inclusions in the present RH refining time. Aiming to generate 12CaO·7Al2O3 inclusions quickly, moderate calcium treatment as a supplementary measure for refining slag is recommended to modify inclusions during the RH refining process.

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Solidification Behavior of Ti-6Al-4V Alloy

Hideo Mizukami, Yoshihisa Shirai, Akira Kawakami, Alec Mitchell

pp. 2455-2461

DOI:

10.2355/isijinternational.ISIJINT-2020-089

抄録

It is important to understand the solidification behavior of titanium alloys for optimizing the casting conditions. In this study, to evaluate the solidification behavior of the Ti-6Al-4V alloy, an experiment was conducted using a lab-scale electron beam furnace. After melting the surface layer of the ingot through electron beam heating, the surface layer was allowed to solidify. Based on the measurement results of the cooling curve of the surface of the ingots, it was observed that the solid was subject to undercooling during its formation. The cooling rate of the ingot could be predicted through numerical simulation, for the melting and solidification of the ingot. The primary and the secondary dendrite arm spacing were examined with respect to the cooling rate. The concentrations of Al and V in the dendritic region were analyzed using electron probe microanalysis (EPMA). It is clarified that the Al is segregated into the dendrite core during solidification, and that V is segregated into the interdendritic region.

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Microstructure Evolution and Mechanical Properties Improvement in Magnetic-controlled Electroslag Remelted Bearing Steel

Qiang Li, Zhibin Xia, Yifeng Guo, Zhe Shen, Tianxiang Zheng, Yunbo Zhong

pp. 2462-2470

DOI:

10.2355/isijinternational.ISIJINT-2020-173

抄録

The transverse static magnetic field (TSMF) was introduced into the electroslag remelting (ESR) process to produce GCr15 steel ingots and the microstructure, non-metallic inclusions, chemical composition and mechanical properties of the ingots were analyzed to investigate the effect of TSMF during the ESR process. The transverse section of the ingots indicated that the application of a 130 mT static magnetic field resulted in a refined dendritic structure. The coverage ratio of the homogeneous crystallites area in the center of the transverse section increased to 52%. The metallic solid-liquid interface with different magnetic flux density (MFD) was recorded during ESR process. The depth of the metallic molten pool was 44.2 mm without the TSMF. When a 130 mT TSMF was applied, the molten pool became noticeably shallower (14.2 mm). And the oxide inclusions count in the scan area of 5.117 mm2 decreased to 239 from 1212. When the TSMF implemented, the tensile, friction and wear and Rockwell hardness properties of ingots showed a significant improvement. These results showed that the application of TSMF during the ESR process of GCr15 steel not only refine the dendritic structure, but also improve the efficiency of inclusion removal and mechanical properties.

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Fuel Ratio Optimization of Blast Furnace Based on Data Mining

Xiuyun Zhai, Mingtong Chen, Wencong Lu

pp. 2471-2476

DOI:

10.2355/isijinternational.ISIJINT-2020-238

抄録

Despite the age of the process, the blast furnace (BF) ironmaking is still crucial to iron and steel industry. To improve the competitiveness of enterprises, fuel ratio (FR) in BF ironmaking process needs to be kept its lowest level possibly. In the work, a prediction model was established to predict FR of the BF by using feature selection and support vector regression (SVR). GA-SVR (genetic algorithm - SVR) method was employed to select the most informative five features from the candidate features.The experimental results indicated that the SVR model brought high learning precision and excellent prediction generalization ability. To explore and discover the laws of BF production, the influences of the five features on FR were discussed by simulation analysis of the model. All the calculations were performed on the computational platform of data mining developed by us. The work can provide guides for the operators on modulating input parameters in advance. The methods outlined here can provide valuable hints into revealing mechanisms of BF ironmaking process and realizing controlled production of BF with guidance of quantitative analysis methods.

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Experimental and Numerical Investigation of the Vibration Characteristics in a Hot Plate Rolling Mill Based on Multibody Dynamics

Hun Bong Lim, Hyun Ik Yang

pp. 2477-2484

DOI:

10.2355/isijinternational.ISIJINT-2019-773

抄録

Analysis of chatter vibration characteristics is an important factor that determines the quality of the slab in a rolling process. A numerical model is proposed to investigate the vibration characteristics. A hot plate rolling mill that includes the driving system is modeled by multibody dynamics to investigate the cause and characteristics of the chatter vibration. Since the spindle of a thick plate hot rolling mill is inclined within 2 degrees depending on the connection part, it is necessary to take into account the elastic effect of the spindle deflection. Therefore, the rigid body model of the previously studied method and the flexible body model that can consider the elastic effect were compared with the experimental model and the accuracy was verified. The chatter frequency was analyzed according to the rolling process and compared with the theoretical calculation results to investigate what occurred during the rolling process. The chatter frequency was compared with the natural vibration frequency of the spindle connected to the work roll and could be expected to be directly related to the bending vibration.

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Numerical Analysis for Jet Impingement and Heat Transfer Law of Self-Excited Pulsed Nozzle

Fubo Zhang, Shuai Wang

pp. 2485-2492

DOI:

10.2355/isijinternational.ISIJINT-2020-001

抄録

The nozzle is the key component of ultra-fast cooling equipment in hot-rolling steel industry, which is crucial for improving the cooling performance. In this paper, in order to optimize the TMCP ultra-fast cooling technology, a self-excited pulsed nozzle was applied into the ultra-fast cooling equipment, and its cooling performance of jet impingement was studied. The flow states and heat transfer characteristics on the surface of the 840°C steel plate, which were impinged by the conventional cylindrical convergent nozzle and self-excited pulsed nozzle formed by adding a Helmholtz oscillating chamber, were simulated by using ANSYS-Fluent under the same inlet pressure, respectively. The maximum jet velocities, dynamic pressures, outlet flow rates of the two nozzles, the temperatures and heat fluxes of the plate surface were monitored. The results showed that, under the pressure of 0.8 MPa, the average outlet flow of the self-excited pulse nozzle was lower than that of the cylindrical convergent nozzle, whilst the self-excited pulse nozzle had higher instantaneous outlet velocity and dynamic pressure. The self-excited pulsed jet could increase turbulence intensity and heat flux on the plate surface. Compared with continuous jet impingement, the self-excited pulsed jet impingement had a better heat transfer effect with lower energy input. The results of the study can provide data support for nozzle designing and better application of ultra-fast cooling equipment.

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Enhanced Homogeneity of a Flat-rolled Wire in Twinning-induced Plasticity Steel Using the Pass Schedule Design

Joong-Ki Hwang

pp. 2493-2502

DOI:

10.2355/isijinternational.ISIJINT-2020-029

抄録

The effects of reduction in height per pass, roll diameter, and friction coefficient on the homogeneity of mechanical properties and shape change in flat-rolled twinning-induced plasticity steel wire were investigated. The goal was to improve the homogeneity of mechanical properties of a wire with area during flat rolling process using a numerical simulation, a hardness test, and electron backscatter diffraction techniques. Reduction in height per pass and roll diameter had large influences on both strain inhomogeneity and lateral spread of flat-rolled wire. Strain inhomogeneity and lateral spread increased with increasing the reduction in height per pass and roll diameter due to the higher length of the contact area. The underlying mechanism for the strain inhomogeneity and lateral spread of flat-rolled wire was highly related to the length of contact area. Hence, the length of the contact area needed reduction through controlling process conditions to improve the strain homogeneity of the flat-rolled wire. The effect of friction coefficient on lateral spread was negligible, whereas strain inhomogeneity slightly increased with friction coefficient. The combination of high and low reduction in height per pass with a smaller roll diameter improved the homogeneity of mechanical properties and microstructure over the area of the flat-rolled wire. Based on the results of numerical simulation and experimental test, a new practical strategy is proposed to achieve greater homogeneity of mechanical properties over the area of flat-rolled wire, which could be of great applicability in industrial fields.

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Numerical Modeling of the Inclusion Behavior during AC Flash Butt Welding

Md Irfanul Haque Siddiqui, Dereje Degefa Geleta, Gyuyeol Bae, Joonho Lee

pp. 2503-2511

DOI:

10.2355/isijinternational.ISIJINT-2020-143

抄録

The entrapment of inclusions in the solidified weld zone is detrimental to its mechanical properties. In an AC flash welding process, the upsetting rate, the initial temperature of the weld pool, and the size of inclusions may affect the final distribution of the inclusions. Additionally, the concentration of sulfur may induce Marangoni convection in the weld pool, which possibly affects the pushing and engulfment of inclusions by the solid at the solid-liquid interface. In the present work, a two-dimensional numerical model based on Computational Fluid Dynamics (CFD) has been developed to investigate the behavior of alumina inclusions during the AC flash welding of a thin SPFH590 steel plate. The Volume of Fluid (VOF) numerical model was coupled with the dynamic mesh model for the motion of plates, discrete phase for inclusion particles and solidification model. The simulation results show that the upsetting parameters significantly affect the overall inclusion motion. A high upsetting rate pushes the inclusions away from the welded joint. The high initial flash temperature does not affect the removal of inclusions from the weld zone. A similar outcome has been noted with respect to the increase in the diameter of the inclusions. Furthermore, the predicted results show that inclusions are prone to engulfment by the solidification front under the influence of higher interfacial tension between the inclusions and melt. Nevertheless, the inclusion displacement under the influence of an interfacial tension gradient is diminutive because of the rapid solidification rate of the weld pool.

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Effects of Solid-Solute V on the Phosphatability of Hot-Rolled Steel Sheets

Shinichi Furuya, Kazuhiko Yamazaki, Hiroyuki Masuoka, Akira Matsuzaki, Shoichiro Taira

pp. 2512-2518

DOI:

10.2355/isijinternational.ISIJINT-2020-133

抄録

The phosphatability of hot-rolled steel sheets has become increasingly important with application of higher strength and thinner steel sheets to automotive parts. Although vanadium (V) is an alloying element which is often added to high strength hot-rolled steel sheets, the effect of V on phosphatability was still unclear. This study investigated the phosphatability of V-added hot-rolled steel sheets by using V-free, 0.20% V, and 0.47% V steel sheets as test specimens. After phosphate treatment, phosphate crystals covered the whole surface of the V-free and 0.20% V steel sheets, but no phosphate crystals were observed on the surface of the 0.47% V steel sheets. In order to clarify this difference, potentiostatic polarization measurement was carried out in the phosphate treatment solution. Phosphate crystals were found on the surface of the V-free steel sheet after both cathodic and anodic polarization. In contrast, no phosphate crystals were found on the surface of the 0.47% V steel sheet after anodic polarization, but similarly to the V-free steel sheet, phosphate crystals had formed after cathodic polarization. A surface analysis by XPS revealed that V oxides had precipitated on the surface of the 0.47% V steel sheet after anodic polarization. V oxidation reaction involves the generation of hydrogen ions and prevent the steel/solution interfacial pH from rising. This reaction identified as the deterioration mechanism of the phosphatability of V-added hot-rolled steel sheets.

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Relationship between Morphology of Mn Oxides Simulated by Ion Plating and Phosphatability of Mn-added High-strength Cold-rolled Steel Sheets

Hiroyuki Masuoka, Shinichi Furuya, Hayato Takeyama, Shoichiro Taira, Akira Matsuzaki

pp. 2519-2524

DOI:

10.2355/isijinternational.ISIJINT-2020-100

抄録

It is well known that Si, Mn and B, the alloying elements for high-strength steel sheets, easily form oxides on the steel surface during annealing in a reducing atmosphere, and those oxides have a large influence on the surface performance of steel sheets, such as phosphatability. In this work, we discovered that the oxidation behavior of Mn-added high strength cold-rolled steel sheets could be simulated on mild steel sheets by using an ion plating method and investigated the relationship between the morphology of Mn oxides and phosphatability under the condition that both the amount and kind of Mn oxides were fixed. In a simulated Mn–O layer, fine surface oxides, which covering most of the steel surface, were observed after annealing. On the other hand, in a Mn–B–O layer, large globular surface oxides were observed on the steel surface, and the Fe surface was partially bare. The B–Mn compound oxide is considered to be in a molten phase during annealing because the melting point of the compound oxide is lower than the annealing temperature, and as a result, it is thought that large B–Mn compound oxides coagulate and grow during annealing. In addition, it was found that the large B–Mn compound oxides (about 500 nm) interfere with steel dissolution in the phosphate solution. These results demonstrate the importance of controlling the morphology as well as the amount and kind of surface oxides for obtaining good phosphatability of Mn-added high strength cold-rolled steel sheets.

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Effect of Microstructure at Coating Layer on Fatigue Strength in Hot-Dip Galvanized Steel

Kayo Hasegawa, Motoaki Morita, Shinichi Motoda

pp. 2525-2532

DOI:

10.2355/isijinternational.ISIJINT-2020-208

抄録

To understand the fatigue mechanism of hot-dip galvanized steel, the fatigue strength and fracture surface of hot-dip galvanized AISI 1045 steel(carbon steel) specimens were investigated. The galvanized coating layer was composed of δ1-phase, ζ-phase and η-phase, and its thickness was about 100 µm. In the low cycle region (104 cycles < Nf < 105 cycles), the fatigue strengths of both the carbon steel and the galvanized steel corresponded with the static strength. The fatigue strength of the galvanized steel was lower than that of carbon steel. As the number of cycles increased, the difference between fatigue strength of the carbon steel and that of the galvanized steel increased. Also, the morphologies of the fatigue fracture were different in low cycle region and high cycle region. In the galvanized steel, the morphology of Stage II crack on the fracture surface at low cycle region exhibited crescent shape, and multiple crack initiation sites in low cycle region were observed. Whereas the morphology at high cycle region (Nf >105 cycles) exhibited an ellipse shape, and the crack initiation site was single. At both regions, the crack initiation sites were in the coating layer. The mechanical properties of the microstructure in the coating layer had an effect on the fatigue strength. When η-phase was removed from the galvanized coating layer, the fatigue strength increased only in the high cycle region. Therefore, δ1-phase and/or ζ-phase cause the fatigue strength to decrease in low cycle region, and η-phase causes it in high cycle region.

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Influence of Soil Particle Size, Covering Thickness, and pH on Soil Corrosion of Carbon Steel

Ryo Hirata, Waka Yonemoto, Azusa Ooi, Eiji Tada, Atsushi Nishikata

pp. 2533-2540

DOI:

10.2355/isijinternational.ISIJINT-2020-261

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The effects of environmental factors, such as particle size, covering depth, and pH, on the corrosion behavior of carbon steel in silica sand filled with a 3% NaCl solution were investigated by electrochemical impedance spectroscopy (EIS) and polarization measurements.The corrosion rate initially decreased with the decrease in the oxygen concentration near the steel surface, which was a result of the consumption of the dissolved oxygen during the corrosion reaction. The corrosion rate became constant at approximately 10 μm y−1 regardless of the particle size and covering thickness. At the steady state, both the anodic reaction (iron dissolution) and cathodic reaction (oxygen reduction) appeared to be suppressed by the formation of an oxide film on the steel surface. In the silica sand filled with non-buffer and buffer solutions of pH 3–6, the corrosion rate was initially significantly enhanced by the hydrogen ions (H+). The period of the enhancement depended on the buffering capacity. However, the corrosion rate was subsequently independent of the pH due to the neutralization of the solution in the vicinity of the steel surface.

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Role of Inclusion, Microstructure and Texture Evolution in Soft Magnetic Properties of Fe–6.9 wt%Si Alloy with Yttrium Doping

Guojun Cai, Ying Li, Yanru Huang, Raja Devesh Kumar Misra

pp. 2541-2548

DOI:

10.2355/isijinternational.ISIJINT-2019-743

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The role of inclusion, microstructure and texture evolution in soft magnetic properties of Fe–6.9 wt%Si alloy with yttrium doping was studied. The results demonstrated that rare earth Y played a crucial role in the soft magnetic properties of Fe–6.9 wt%Si alloy. Adding Y suppressed the nucleation of {110} orientation grains at {111} in-grain shear bands during warm rolling, and refined the grain size after annealing. Meanwhile, the average size and number of inclusions showed a similarly decreasing trend because of Y doping, and the maximum interface energy between fine Y-inclusions and {100} grains possibly induced the grain growth of {100} grains. In the measurement of magnetic properties, B8 value increased from 1.295 T to 1.493 T, and P10/1000 value was reduced from 19.165 W/kg to 17.328 W/kg due to Y doping.

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Effects of Concentrations of Micro-alloying Elements and Hot-forging Temperature on Austenite Grain Structure Formed during Carburization of Case-hardening Steel

Genki Saito, Norihito Sakaguchi, Munekazu Ohno, Kiyotaka Matsuura, Masayoshi Takeuchi, Taichi Sano, Koki Minoguchi, Takuya Yamaoka

pp. 2549-2557

DOI:

10.2355/isijinternational.ISIJINT-2020-123

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Effects of fine precipitates on the austenite (γ) grain structures were investigated in JIS SCM420-based case-hardening steels with several different concentrations of the micro-alloying elements and hot-forging temperatures. Micro-alloyed steels of 18Al (0.018 mass% Al) and 35Al–32Nb (0.035 mass% Al, 0.032 mass% Nb) were forging-simulated at 1150°C or 1250°C, normalized at 1070°C, and carburized at 1050°C. When the as-received 18Al steel was normalized and carburized without forging-simulated heating, a uniform γ grain structure was observed with the distribution of fine AlN precipitates. However, coarsening of AlN occurred when the forging-simulated temperature was 1150°C and it caused abnormal grain growth during carburization. In 35Al–32Nb steel, the same heating did not induce the abnormal grain growth owing to the AlN–Nb(C,N) combined particles. The size of these particles increase with an increase in the forging-simulated temperature. The high forging-simulated temperature caused the dissolution of the fine precipitates, followed by reformation and coarsening of the precipitates during the subsequent cooling and the normalization heating, which resulted in a decreased pinning force and γ grain coarsening. Furthermore, TEM observations revealed that a considerable amount of Nb(C,N) particles exist near large eutectic MnS particles. Thermodynamic calculations based on the Scheil’s condition showed that the formation of these Nb(C,N) particles was due to segregation during solidification. It was suggested that such local concentration of the precipitate particles in the last solidifying region leads to ununiform distribution of the pinning force that may induce the abnormal grain growth.

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Recrystallization Behavior and Formation of {411}<148> Grain from α-fiber Grains in Heavily Cold-rolled Fe-3%Si Alloy

Masato Yasuda, Kenichi Murakami, Kohsaku Ushioda

pp. 2558-2568

DOI:

10.2355/isijinternational.ISIJINT-2020-161

抄録

Recrystallization texture is essential to control the mechanical and magnetic properties of steels. Both γ-fiber (ND//<111>) and α-fiber (RD//<011>) textures are known to develop during the rolling process of bcc iron. Recrystallization behavior from γ-fiber has been extensively studied. On the other hand, recrystallization behavior from α-fiber, in particular after heavy cold rolling reduction, has not been sufficiently clarified. In this study, recrystallization behavior from α-fiber, focusing on the formation of {411}<148> recrystallized grain, was investigated by means of EBSD and TEM. {411}<148> region already existed in the vicinity of deformed grains having upper α-fiber orientation({100}<011>~{211}<011>). TEM observation revealed the existence of the lamellar structure with {411}<148> relatively fine dislocation cells in the {211}<011> deformed grains. With the progress of the recovery, {411}<148> subgrains (dislocation cells) are postulated to easily form and are surrounded by the deformed matrix grains with high angle interface. Thus, it is easy to form the recrystallization nuclei having the potential to grow with the sake of both high driving force and high interface mobility. At the early stage of recrystallization, {411}<148> recrystallized grains developed in {211}<011> deformed grains. At the later stage, {411}<148> recrystallized grains from {211}<011> deformed grains encroach {100}<011> deformed grains and new {411}<148> recrystallized grains developed in {100}<011> deformed grains.

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Heat Treatment Effect on the Microstructure and Tribological Behaviour of a High Chromium Cast Iron with 0.5% of Niobium

Leonardo Menezes de Faria, Ismael Nogueira Rabelo de Melo, Anderson Júnior dos Santos, Ivete Peixoto Pinheiro

pp. 2569-2575

DOI:

10.2355/isijinternational.ISIJINT-2019-760

抄録

A high chromium cast iron (HCCI) with 0.5%Nb was subjected to destabilization heat treatments (950°C, 1000°C, and 1050°C) for 2 hours. Specimens were characterized by optical and scanning electron microscope (SEM). It was found coarser secondary carbides as the temperature treatment increased. Niobium carbides were found agglomerated in petal-like and blade-like forms. Abrasion tests using a Dry Rubber Wheel Abrasion Tester (DRWAT) were carried out. Results indicated that the wear resistance was proportional to the matrix microhardness, the 1000°C and 1050°C temperatures presented the best wear resistance. SEM images have shown wear by plastic deformation preferentially on the matrix. The worn surfaces were scanned by a contact profilometer. Specimens which had more removed material presented a higher average roughness (Sa). Also, the average roughness (Sa), maximum values of peaks (Sp) and pits (Sv) tended to be lower as the temperature of the heat treatment increased. This can be related to the plastic deformation caused by the wear. The presence of pits was predominant on the worn surfaces.

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Crack Propagation Behavior of Impact Fracture in Case Hardening Steel Subjected to Combined Heat Treatment with Excess Vacuum Carburizing and Subsequent Induction Hardening

Kazuaki Okada, Koji Obayashi, Yoshikazu Todaka, Nozomu Adachi

pp. 2576-2585

DOI:

10.2355/isijinternational.ISIJINT-2019-826

抄録

The Charpy impact value of case hardening steel subjected to combined heat treatment with excess vacuum carburizing and subsequent induction hardening was evaluated. The purpose of this study is to clarify the relation between the crack propagation behavior and the microstructure in steels having different amounts of retained austenite and cementite. The vacuum carburizing treatment is performed at the hyper-eutectoid composition of 1.3 mass% C. Three different heating temperatures were chosen for induction hardening in the two-phase (austenite, cementite) region between Acm and A1 to obtain different amounts of retained austenite and cementite. Decreasing the induction heating temperature from 1143 K to 1043 K, increased crack propagation resistance by around 30% on average in both the quenched-only and the quenched-and-tempered specimens. The high crack propagation resistance of the samples with the low induction heating temperature was caused by the arrest effect of undissolved θ. By contrast, in the sub-zero treated specimens, crack propagation resistance showed an almost constant value irrespective of the induction heating temperature. That constant propagation resistance was attributed to the repeated bending and branching occurring during crack propagation.

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Microstructure, Mechanical Properties and Wear Resistance of Low Alloy Abrasion Resistant Martensitic Steel Reinforced with TiC Particles

Long Huang, Xiangtao Deng, Qi Wang, Zhaodong Wang

pp. 2586-2595

DOI:

10.2355/isijinternational.ISIJINT-2020-139

抄録

The TiC-reinforced low alloy abrasion resistant martensitic steel was developed to improve the wear resistance without increasing hardness through traditional melting and casting technology and subsequent hot rolling and heat treatment processes. The new wear resistant steel was reinforced with micron- and nano-sized TiC particles. The phase diagram calculated by Thermal-Calc software indicated that micron-sized TiC particles precipitates towards the end of solidification. The hot rolling process changed the distribution of initial micron-sized TiC particles and transformed it from a segregated distribution to a uniform distribution. Amounts of nano-sized precipitation was obtained via pre-tempering treatment, which remarkably improved the three-body abrasive wear performance of TiC reinforced steel at the expense of a little ductility and toughness. The steel reinforced with only micron-sized TiC particles, whose wear resistance was 1.35 times that of conventional abrasion resistant steel (NM500). However, the steel reinforced with micron- and nano-sized TiC particles, whose wear resistance increased to 1.5 times that of NM500. The wear mechanism of conventional steel was micro-cutting/micro-ploughing, while the wear mechanism of TiC-reinforced steel was spalling and fatigue, because the micro-cutting was efficiently resisted by TiC particles.

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Mechanism Behind the Onset of Delamination in Wire-drawn Pearlitic Steels

Masaki Tanaka, Toshiyuki Manabe, Tatsuya Morikawa, Kenji Higashida

pp. 2596-2603

DOI:

10.2355/isijinternational.ISIJINT-2020-158

抄録

Fully pearlitic steel was wire-drawn up to a strain of 2.2. Torsion tests were performed using two types of specimens—one was an as-drawn specimen, and the other was aged at 423 K for 3.6 ks. A delamination crack propagated along the longitudinal direction of the wire in the aged specimen, whereas normal fracture was exhibited perpendicular to the longitudinal direction in the as-drawn specimen during torsion tests. Backscattered electron images indicated that the cementite lamellae beneath the delamination crack had vanished, whereas, in the as-drawn specimen, the cementite lamellae beneath the normal fracture surface had rotated until the fracture. Torsion tests with different strain rates indicated an inverse strain-rate dependence of the onset of the delamination, suggesting that the plastic deformability of ferrite and existence of the thermally activated process that controls the cementite dissolution indicate the onset of the delamination. In the present study, the effect of aging and deformability of ferrite on delamination is discussed, suggesting that the delamination crack propagates as a result of the local plastic instability on the scale of several microns.

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Availability of Opal Photonic Crystal Films for Visualizing Heterogeneous Strain Evolution in Steels: Example of Lüders Deformation

Zhipeng Yang, Motomichi Koyama, Hiroshi Fudouzi, Tomohiko Hojo, Eiji Akiyama

pp. 2604-2608

DOI:

10.2355/isijinternational.ISIJINT-2020-223

抄録

An opal photonic crystal film was applied to characterize local strain evolution associated with Lürders band propagation in an annealed low carbon steel. A local change in color of the opal film was observed, which corresponded to the propagation of the Lürders band. In particular, we carried out two tensile experiments for line and area analyses of RGB (Red-Green-Blue) values of the opal films pasted on the specimens. Both of the experiments clearly exhibited a quantitative correspondence between color variation and local strain evolution, namely, the present study demonstrated the potential of the opal films to analyze heterogeneous strain evolution in steels.

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Improvement of Rigidity of Super Invar Cast Steel via Austenite Recrystallization Induced by Martensitic Reversion

Naoki Sakaguchi, Kotaro Ona, Rui Bao, Nobuo Nakada

pp. 2609-2614

DOI:

10.2355/isijinternational.ISIJINT-2020-254

抄録

Super invar cast steel, 32mass%Ni-5mass%Co, with an excellent low thermal expansion coefficient exhibits very low Young’s modulus due to a course solidified columnar structure with <100> austenite texture. For the improvement of the low Young’s modulus, a novel heat treatment consisted of subzero treatment and subsequent annealing was applied to stimulate microstructure evolution accompanied with texture variation. Lenticular martensite preferentially formed along a dendrite structure with lower Ni concentration after subzero treatment at liquid nitrogen temperature and then reversed into austenite again by the subsequent annealing above 873 K via diffusionless shear mechanism, that is, martensitic reversion took place. Since the martensitic reversion realizes a crystallographic reversibility, the course columnar structure at initial state was reconstructed after the completion of reversion. Furthermore, the course structure formed via martensitic reversion recrystallized to equiaxed fine-grained structure when the annealing temperature became higher, because high density dislocations in martensitic reversed austenite caused by the invariant lattice deformation on two directional martensitic transformations drives the austenite recrystallization. The recrystallization leads to the formation of fine-grained austenitic structure with random orientation, and as a result, Young’s modulus of super invar cast steel was improved to be as high as the forged one without any plastic deformation process.

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Development of Fe–P–C–Cu Immiscible Amorphous Alloys with Liquid Phase Separation

Takeshi Nagase, Tomoyuki Terai, Mitsuaki Matsumuro, Mamoru Takemura

pp. 2615-2624

DOI:

10.2355/isijinternational.ISIJINT-2020-211

抄録

The rapid solidification microstructure and magnetic properties of melt-spun ribbons in the (Fe0.75P0.125C0.125)100-xCux (at%) alloys were investigated, focusing on the occurrence of liquid-phase separation and simultaneous amorphous-phase formation. The (Fe0.75P0.125C0.125)100-xCux alloys were designed as a combination of Fe–P–C alloy with high glass-forming ability and Cu. Amorphous-phase formation was observed in the melt-spun ribbons of the (Fe0.75P0.125C0.125)100-xCux (x = 10, 20) alloys. For the melt-spun ribbons of the (Fe0.75P0.125C0.125)100-xCux (x = 10) alloy, a composite of Fe–P–C amorphous matrix and FCC–Cu globules was obtained, whereas in the melt-spun ribbons of the (Fe0.75P0.125C0.125)100-xCux (x = 20) alloy, multistep liquid-phase separation resulted in a particular solidification microstructure.

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Application of Electroextraction in Removing Copper from Molten Iron

Zhihao Lu, Chengjun Liu

pp. 2625-2627

DOI:

10.2355/isijinternational.ISIJINT-2020-097

抄録

An innovative attempt of applying electrochemical method in solving the residual copper challenge in iron and steel was proposed in this paper. The ionic conductivity of the sulfide slag has been found in study of copper removal from iron-based melt by Na2S–FeS system. A DC electric field was applied between sulfide melt and iron melt, which could electrolyze the product Cu2S, so that the activity of Cu2S in the sulfide slag was reduced and the selective sulfurization of copper in the iron was promoted. The cathodic process was studied by Voltammetry test and Potentiostatic electrolysis test, the results indicated that the Faradaic reactions indeed occurred and the directional mass transfer of copper was promoted by applying the electric field. In the results of copper removal test by electroextraction, the applied DC electric field broke the interface reaction equilibrium between sulfide slag and copper bearing carbon saturated iron melt and reduced the copper content significantly.

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Erratum to “Neural Network Modelling on Contact Angles of Liquid Metals and Oxide Ceramics” [ISIJ International, Vol. 60 (2020), No. 8, pp. 1586-1595]

Peiyuan Ni, Hiroki Goto, Masashi Nakamoto, Toshihiro Tanaka

pp. 2628-2628

DOI:

10.2355/isijinternational.60.2628

抄録

The following text will be added above the Acknowledgments.The editorial office expresses sincere apology for the misprinting. Supporting Information (Appendix data):This material is available on the Website at https://doi.org/10.2355/isijinternational.ISIJINT-2019-640.

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