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ISIJ International Vol. 62 (2022), No. 11

ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559
Publisher: The Iron and Steel Institute of Japan

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  1. Vol. 64 (2024)

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ISIJ International Vol. 62 (2022), No. 11

Deformation of Non-metallic Inclusions in Steel during Rolling Process: A Review

Ying Ren, Wen Yang, Lifeng Zhang

pp. 2159-2171

DOI:

10.2355/isijinternational.ISIJINT-2022-235

Abstract

Non-metallic inclusions were deformed and broken during hot and cold rolling processes. The deformation of inclusions during the rolling process had an influence on the property of steel products. Investigations on the deformation of inclusions in steel was reviewed in the current study. Physical properties of inclusions were summarized and compared, such as the melting temperature, viscosity, Young’s modulus, hardness, thermal expansion coefficient, crystallization, and Poisson’s ratio. The deformability index of inclusions showed a decreasing tendency with a higher rolling reduction. During the hot rolling process, the deformability index of oxide inclusions was mainly related to the melting temperature and viscosity of inclusions. With the increase of the rolling temperature, the deformability index of oxide inclusions showed an increasing tendency due to the higher liquid fraction and the lower viscosity of inclusions. During the hot rolling process, the deformability index of MnS inclusions increased with a decrease of the rolling temperature until reaching the austenite to ferrite matrix transformation temperature. During the cold rolling process, deformability index of oxide inclusions was mainly influenced by Young’s modulus and hardness of inclusions. Inclusions with a lower Young’s modulus exhibited a higher deformability index during the cold rolling process. Moreover, the focus on the inclusion deformation in the future was proposed in this paper.

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Deformation of Non-metallic Inclusions in Steel during Rolling Process: A Review

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Review on the Viscosity of Iron-based Melts in Metallurgical Process

Shanchao Gao, Kexin Jiao, Jianliang Zhang, Xiaoyue Fan, Zhengjian Liu, Anyang Zheng

pp. 2172-2182

DOI:

10.2355/isijinternational.ISIJINT-2022-217

Abstract

Low-carbon metallurgy is a critical issue for the world in the 21st century and improving production efficiency is one of the main ways to resolve this problem. Iron-based alloy runs through the whole process of metallurgy, and the viscosity properties of melt is of great significance on the process of reaction, transportation and solidification casting, which is one of the constraints on production efficiency. The research progress of the viscosity of iron-based melt is summarized from the aspects of measurement methods, influencing factors and prediction models in this paper. It is briefly concluded that the oscillating method is the most widely used measurement method of iron-based melts and pointed out that the interaction between the components and the formation of inclusions will have a significant effect on the viscosity of iron-based melts. And the three semi-empirical models derived from the Andrade equation can be applied to the viscosity prediction of molten iron as the pre-revised basic equations with greater precision. Then the direction of iron-based melt viscosity research in the future is prospected at last.

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Review on the Viscosity of Iron-based Melts in Metallurgical Process

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Digital Twin Science of Metal Powder Bed Fusion Additive Manufacturing: A Selective Review of Simulations for Integrated Computational Materials Engineering and Science

Yuichiro Koizumi, Masayuki Okugawa

pp. 2183-2196

DOI:

10.2355/isijinternational.ISIJINT-2022-184

Abstract

A digital twin (DT) is a cyberspace replica of a system, such as manufacturing equipment. A DT consists of statistical models and computer simulations of physical phenomena occurring in the system. The modeling is adjusted to the system based on signals from sensors attached to the system and their temporal changes. In general, a DT is utilized to (i) predict phenomena occurring in the system, (ii) optimize control parameters, and (iii) estimate part replacement schedules. We propose to use a DT to elucidate the unique solidification phenomena occurring in a type of metal 3D printing (i.e., additive manufacturing: AM) process. Thus, we propose that applications of DT that obtain scientific data be referred to as “digital twin science (DTS).” This paper first reviews the fundamental of the AM process, particularly powder bed fusion (PBF) and relevant computer simulations, and then studies on computer simulations conducted to elucidate the relationship between the extreme conditions characteristic of the PBF process and solidification microstructures. The findings achieved by the DTS approach indicate that the combination of experimental and simulation data aid the future development of techniques to obtain required microstructures exhibiting desired properties.

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Digital Twin Science of Metal Powder Bed Fusion Additive Manufacturing: A Selective Review of Simulations for Integrated Computational Materials Engineering and Science

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Effect of Cooling Method on the Mineralogy and Stability of Steel Slag

Yongda Li, Kunpeng Guo, Junyi Xiang, Guishang Pei, Xuewei Lv

pp. 2197-2206

DOI:

10.2355/isijinternational.ISIJINT-2022-101

Abstract

Steel slag, as a potentially active gelling material, has not been widely used in the field of building materials. The effective utilization of steel slag depends on its stability, which is related to the cooling process with phases changing. The relation between cooling method and the phases and stability of steel slag were carried out in the present study. The slags were first melted into liquid state at 1873 K and were then cooled using four cooling methods, namely, as-furnace cooling, air cooling, mist cooling and water quenching. The cooled slags were characterized by XRD, SEM, and chemical analysis. The results show that the slags under the four cooling methods mainly contained Ca2SiO4 (C2S), Ca2SiO4–Ca3P2O8 solid solution (C2SP), Ca3SiO5 (C3S), monoxide solid solution (RO), Ca2Fe2O5 (C2F), and f-CaO. The content of Ca3SiO5 in steel slag increased with the increase of cooling rate. Rapid cooling could reduce the content of RO phase in steel slag, and the content of RO phase for the furnace cooling, air cooling, mist cooling, and water quenching samples were 28.03%, 22.53%, 14.17%, and 13.30%, respectively. In addition, rapid cooling could effectively reduce the content of f-CaO in steel slag and improve the stability of steel slag.

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Effect of Cooling Method on the Mineralogy and Stability of Steel Slag

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Effect of Al2O3 on Viscosity and Refining Ability of High Basicity Slag for Heat-resistant Austenitic Stainless Steel

Shucai Zhang, Huabing Li, Mingze Ran, Zhouhua Jiang, Lichun Zheng, Hao Feng, Jiangtao Yu, Yubo Dai

pp. 2207-2216

DOI:

10.2355/isijinternational.ISIJINT-2022-211

Abstract

To optimize Al2O3 content in high basicity CaO-SiO2-Al2O3-8%MgO-8%CaF2 slag (%CaO/%SiO2=6) used for the refining of heat-resistant austenitic stainless steel, the effect of Al2O3 on the viscosity and refining ability of the slag was systematically investigated, and the relevant mechanism was clarified based on the analyses of solid phase precipitation behaviour and ionic unit structure transformation. The results demonstrated that the slag viscosity dramatically decreased and marginally varied in the Al2O3 ranges of 10%–20% and 20%–30%, respectively. At 1833–1873 K, both the slag viscosity and the activation energy reached the lowest values at 25% Al2O3. Al2O3 addition not only significantly inhibited the precipitation of CaO phase but also enhanced the polymerization degrees of aluminate and silicate networks. Furtherly, the inhibiting of Al2O3 on the solid phase precipitation dominated the viscosity reduction at 10%–25% Al2O3, while the enhancing of Al2O3 on the polymerization degree of networks led to the viscosity increase with further increasing Al2O3 to 30%. Finally, we optimized the reasonable high basicity slag containing 25% Al2O3 for Sanicro 25 steel due to the lowest viscosity and optimum refining ability of this slag.

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Effect of Al2O3 on Viscosity and Refining Ability of High Basicity Slag for Heat-resistant Austenitic Stainless Steel

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Effect of Viscosity and Surface Roughness on Improvement of Solid-liquid Wettability by Ultrasonic Vibration

Keiji Okumura, Yuya Tanaka, Kazuhiko Iwai

pp. 2217-2224

DOI:

10.2355/isijinternational.ISIJINT-2022-268

Abstract

In order to investigate the influence of liquid viscosity and surface roughness of the substrate on the improvement of wettability by ultrasonic vibration, a liquid droplet was put on a Langevin type vibrator, and ultrasonic vibration was applied to observe the change of the droplet shape. The droplets were deformed by the application of ultrasonic vibration, and the contact angle between solid and liquid was reduced, so that the wettability was improved. It was considered that the ultrasonic radiation pressure acting inside the droplet had an effect on the deformation of the droplet, and the value of the radiation pressure was estimated based on Laplace’s equation. It was confirmed that when the viscosity of the liquid was high, the change in the shape of the droplet was prevented by an increase in the shear stress for deformation. Regarding the surface roughness, it was found that the pinning effect made it difficult to reduce the contact angle. When the ultrasonic vibration was stopped, the shape of the droplet recovered to some extent before the ultrasonic vibration, but did not completely return to the original shape.

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Effect of Viscosity and Surface Roughness on Improvement of Solid-liquid Wettability by Ultrasonic Vibration

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Numerical Analysis of the Dust Control Performance of a Counter-current Swirling Configuration in the Flash Ironmaking Reactor

Yiru Yang, Zhongjie Shen, Jianliang Xu, Haifeng Liu

pp. 2225-2235

DOI:

10.2355/isijinternational.ISIJINT-2022-092

Abstract

Flash ironmaking technology (FIT) is a potential alternative ironmaking process reducing energy consumption and environmental pollution. The newly proposed counter-current flash ironmaking process has a more reasonable temperature and concentration distribution, while the high dust rate cannot be avoided. In this study, a counter-current swirling configuration was introduced to improve the dust control performance. A comprehensive computational fluid dynamics (CFD) model, including gas-particle motion, chemical reactions, particle-wall sticking, slag movement, and wall reaction, was adopted to investigate the velocity vector, temperature, species distribution under the counter-current swirling flow. The effects of initial particle velocity (IPV) and swirl angle velocity (SAV) were analyzed as the crucial parameters. The results show that an annular updraft-center downdraft structure is formed by swirling flow, and the particles are pushed to the wall under the centrifugal force, adhere to the high-temperature wall, and flow down slowly with the molten slag. In the non-swirl cases, the increase of IPV can effectively inhibit the particles escaping ratio from 62.5% to 22.4% and increase the amount ratio of particles leaving the bottom directly with a lower reduction degree. Therefore, necessary swirling flow enhances the high probability of adhesion when the SAV over a varying critical value related to IPV. Also, the long residence time in the molten slag effectively increases the reduction degree of captured particles from 94.3% to 100%. The comprehensive reduction degree of particles increased from 83.3% to 87.3% in a single-cycle reaction.

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Numerical Analysis of the Dust Control Performance of a Counter-current Swirling Configuration in the Flash Ironmaking Reactor

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Migration Behavior of K, Na, S, Ti in Hearth of a Commercial Blast Furnace

Hengbao Ma, Zhengjian Liu, Jianliang Zhang, Tianlu Gao, Yanbing Zong, Ziyu Guo, Kexin Jiao

pp. 2236-2243

DOI:

10.2355/isijinternational.ISIJINT-2022-097

Abstract

In-depth understanding of the existence state and migration behavior of K, Na, S, Ti in the BF hearth is essential to improve the campaign life and optimize the operation process of the blast furnace. In the study, deadman and carbon brick samples were extracted along the radial direction from a large commercial BF during dissection investigation. The microscopic morphology of the samples and the migration behavior of K, Na, S, Ti were analyzed. It was found that a layer of minerals existed on the surface of deadman coke in hearth, and high melting temperature phases such as CaS and TiN as well as slag with high aluminum were existed at the coke-slag-iron interface. K, Na compound present widespread in the deadman coke and carbon brick. The formation of mineral layer reduced the coke dissolution rate, thereby delaying the renewal rate of the deadman. With the dissolution of coke, minerals flow out from the surface of coke and precipitate as alumina and MgAl2O4 spinel, which reduces the voidage of the deadman. Meanwhile, slag is sufficiently desulfurized with the iron to form a large amount of CaS accumulation at the hearth sidewall, which intensifies the iron circulation and increases the erosion of carbon brick. When the slag is in contact with the refractory, the K, Na contained in the slag provides a source of alkalis attack on the carbon bricks, and the Ti in the slag provides the possibility of forming a protective layer containing titanium on the sidewall of the hearth.

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Migration Behavior of K, Na, S, Ti in Hearth of a Commercial Blast Furnace

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Improvement of Sinter Productivity and Qualities by Placing Low Slag Green Pellet at Lower Layer of Sinter Packed Bed

Masaru Matsumura, Yasuhide Yamaguchi, Kenichi Higuchi, Taichi Murakami, Takayuki Maeda

pp. 2244-2254

DOI:

10.2355/isijinternational.ISIJINT-2022-148

Abstract

In order to blend PF (pellet feed) or concentrates for 20 mass% in sinter mixture and to displace coke fines or anthracite to biomass for 25 mass% in BAR (Bonding Agent Rate), sinter packed bed has been designed in ISIJ Research workshop. Outline of the design is shown as below.As designing, most important factor is permeability, and it has to be maintained even though fine materials as PF or concentrates is highly blended (20 mass%). For high permeability, GP [Green Pellet] granulated from fine materials, is placed in lower layer of raw materials packed bed. In the lower layer, mill scale and biomass char, which has characteristic of different oxidation or combustion temperature and rate compared to coke fine, are placed with coke fines for keeping high temperature (>1200°C), because GP needs longer sintering time due to large diameter. In addition, chemical composition of GP is low bacisity (1.5) and low CaO content for keeping its shape through restricting melt formation at sintering. Restricting melt formation has possibility of improving sinter quality (RI,RDI).In this study, Effect of the packed bed mentioned above on sinter performance and quality has been confirmed by sintering simulator which has performance of continuous charging and igniting with moving pallet car.The main results are shown as below.1) Sintering speed and product yield are maintained at blending 20 mass% of PF. So, sinter productivity are also maintained.2) Sinter reducibility (RI) has been improved in addition to maintaining sinter reduction disintegration index(RDI) because of low FeO and low SiO2 content and restricting secondary hematite formation as mineral of sinter.3) Remaining object is recovering sinter strength (TI) at the condition of low CaO content in sinter.

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Improvement of Sinter Productivity and Qualities by Placing Low Slag Green Pellet at Lower Layer of Sinter Packed Bed

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Effect of Al2O3 and TiO2 Contents in the Refining Slag on Al and Ti Contents of Incoloy825 Alloy

Wei Gong, Rongao Zhou, Pengfei Wang, Zhouhua Jiang, Xin Geng

pp. 2255-2265

DOI:

10.2355/isijinternational.ISIJINT-2022-158

Abstract

During the refining process of Incoloy825 nickel-based alloy, the reaction between the refining slag and Al and Ti in the alloy can result in the oxidation loss. Therefore, the effect of the TiO2 and Al2O3 contents in the refining slag (CaO–SiO2–Al2O3–MgO–CaF2–TiO2) on the final Al and Ti contents in Incoloy825 alloy was investigated by slag-metal reaction experiment in a 1-kg MoSi2 resistance furnace. The thermodynamic model was established based on ion and molecular coexistence theory and the kinetic model was established based on two-film theory. The experimental results show that an increase in TiO2 (Al2O3) content in the slag leads to an increase (decrease) in Ti content and a decrease (increase) in Al content in the final alloy. The thermodynamic model demonstrates that the activities of SiO2, Al2O3, and TiO2 in the slag are negatively correlated with the content of CaO and positively correlated with SiO2, Al2O3, and TiO2 in the slag. The kinetic model indicates that the slag-metal reaction reaches equilibrium within 10 min, and the model has good applicability for the reaction process of Incoloy825 alloy and slag refining.

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ISIJ International Vol.62(2022), No.11

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Effect of Al2O3 and TiO2 Contents in the Refining Slag on Al and Ti Contents of Incoloy825 Alloy

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Characteristics and Formation Mechanism of Complex TiN Inclusions in 20CrMnTi Gear Steel

Yao Li, Guoguang Cheng, Jinlong Lu, Jun Sun

pp. 2266-2275

DOI:

10.2355/isijinternational.ISIJINT-2022-187

Abstract

In this paper, in order to study the effect of oxides on the formation of complex TiN inclusions in 20CrMnTi steel, based on the two end quenching specimens with different components, the characteristics of complex TiN inclusions and oxides were observed and analyzed, and the formation mechanism of complex TiN inclusions was discussed. The results indicate the compositions of core oxides are regularly distributed in the MgAl2O4–TiOx composition line for different complex TiN inclusions, and the difference is the TiOx content. The complex TiN inclusions can be divided into two types, Type 1 and Type 2, based on the compositions of core oxides. For Type 1, TiOx content of core oxides are below 52%, while for Type 2, TiOx content of core oxides are over 52%. The core oxides of Type 1 have bigger size at the range of 1–3 µm, and lower nucleation capability for TiN inclusions. The core oxides of Type 2 have smaller size at the range of 0.5–2 µm, and higher nucleation capability for TiN inclusions. For Type 1, the MgAl2O4–TiOx oxides preexisting in molten steel are the heterogeneous nucleation cores of TiN inclusions during solidification. For Type 2, the tiny oxides newly formed during solidification are the nucleation cores of TiN inclusions. By controlling the characteristics of oxides, the characteristics of TiN inclusions can be controlled, which provides a new idea for the control of TiN inclusions in 20CrMnTi gear steel.

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Characteristics and Formation Mechanism of Complex TiN Inclusions in 20CrMnTi Gear Steel

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Change of Spinel in High Ca Treament at 38CrMoAl Steel

Yang Li, Hao Yang, Zhou-Hua Jiang, Hua-Bing Li, Meng Sun, Shuai Ma

pp. 2276-2285

DOI:

10.2355/isijinternational.ISIJINT-2022-188

Abstract

In this study, 38CrMoAl steel was treated with calcium under the pressure of 2 MPa, and four groups of high aluminum steels with the highest calcium content of 0.01% were obtained. Spinel inclusions with high MgO content, CaO and MgO inclusions with original spinel morphology were found by testing and analyzing the morphology towards composition of inclusions in the high Ca content steel. Combined with thermodynamic calculation, a Ca–Al spinel reaction model was proposed, the solid/liquid phase denaturation mechanism of calcium treated spinel was explored, and the influence of total oxygen content on phase equilibrium in denaturation process was analyzed. At last, it was obtained that the spinel denaturation products is MgO+Spinel, CaO–Al2O3–MgO and CaO–Al2O3 when the mass fraction of calcium was low; And the spinel denaturation products with high calcium content are MgO+Spinel, MgO and CaO.

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Change of Spinel in High Ca Treament at 38CrMoAl Steel

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Characterization and Control of Secondary Phase Precipitation of Nb–V–Ti Microalloyed Steel during Continuous Casting Process

Lei-lei Zou, Jiang-shan Zhang, Qing Liu, Biao Tao

pp. 2286-2293

DOI:

10.2355/isijinternational.ISIJINT-2022-172

Abstract

The strand surface and subsurface cracks could be prevented through the control of the strand surface microstructure, which correlates with the precipitation behavior of carbonitrides in the microalloyed steel. In this study, the carbonitride precipitation behavior was characterized in-situ with a high-temperature confocal laser scanning microscope, and the effects of cooling rate on the morphology and distribution of precipitates was investigated. The results show that the carbonitride precipitation process is usually accompanied by the formation of dark particles due to the volume expansion of the solute depletion region. The evolution of dark particles suggests that carbonitrides mainly precipitate between 910°C and 1085°C, and the “fast-growing region” ranges from 910°C to 960°C. As the cooling rate increases, the size and volume fraction of carbonitrides decrease. Meanwhile, the nucleation location changes from grain boundary to grain interior. To quantify the pinning capacity of the carbonitrides, the pinning force factor σ is defined according to the classical Gladman equation, which is a power function of the cooling rate, namely σ=0.43−0.1(1+2.76Vc3.48)−1. Combining the above research, a new secondary cooling method is proposed and has been applied on an actual caster, which improves the crack resistance of the bloom surface microstructures.

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Characterization and Control of Secondary Phase Precipitation of Nb–V–Ti Microalloyed Steel during Continuous Casting Process

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Numerical Simulation for Magnetohydrodynamic Flow and Solidification in an Ultra-wide Slab Continuous Caster with Electromagnetic Stirring Roller

Lei Fang, Tianyu Liu, Yahe Huang, Weiqin Wu, Wei Feng, Hong Lei

pp. 2294-2300

DOI:

10.2355/isijinternational.ISIJINT-2022-242

Abstract

Electromagnetic stirring with segment roller in the secondary cooling zone is a very important metallurgical technology for the continuous casting of the ultra-wide slab. Thus, numerical simulation is applied to investigate magnetohydrodynamic flow and solidification in the continuous caster with strand electromagnetic stirring. Numerical results showed that, the predicted values agree well with the experimental data. If the electromagnetic stirring roller with the symmetric split structure forms the symmetric magnetic field, there are the symmetric electromagnetic force, the symmetric flow field and the symmetric solidified shell. If the single electromagnetic stirring roller with the symmetric split structure forms the symmetric electromagnetic force, the flow field is like a butterfly. If the two electromagnetic stirring rollers forms the symmetric electromagnetic force, the flow field is like two butterflies. The effect of strand electromagnetic stirring on the fluid flow in the mold can not be ignored in the case of SSR (Same direction for upper rollers, Same direction for lower roller, Reverse direction for relation between upper/lower rollers), and it can be ignored in the case of NAS (No upper rollers, Away direction for lower roller, Single roller for relation between upper/lower rollers) and CAR (Close direction for upper rollers, Away direction for lower roller, Reverse direction for relation between upper/lower rollers).

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Numerical Simulation for Magnetohydrodynamic Flow and Solidification in an Ultra-wide Slab Continuous Caster with Electromagnetic Stirring Roller

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Prediction Model for Vanadium Content in Vanadium and Titanium Blast Furnace Smelting Iron Based on Big Data Mining

Hongwei Li, Xiaojie Liu, Xin Li, Hongyang Li, Xiangping Bu, Shujun Chen, Qing Lyu

pp. 2301-2310

DOI:

10.2355/isijinternational.ISIJINT-2022-037

Abstract

A model for predicting the vanadium content in a molten iron blast furnace (BF) was developed to solve the problem of late iron detection during the smelting process of a vanadium and titanium BF. First, based on the whole process data platform of BF ironmaking, the standardized data warehouse of BF smelting was established, and the variables related to vanadium content in molten iron are selected in the model. Clean data were obtained by processing the original data. Afterward, the feature extraction of variables was achieved by feature construction and PCA dimensionality reduction, and the final input feature variables were determined using a combination of multiple feature selection algorithms and production process experience. Finally, the CatBoost model was selected for prediction. The results show that CatBoost achieved better results than XGBoost and long short-term memory (LSTM) models, and all indicators were higher than in these two models. The R2 of CatBoost reached 0.773, and the index of prediction error within ±0.020% reached 89.65%, which met the actual production requirement of a vanadium and titanium commercial BF in China.

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Prediction Model for Vanadium Content in Vanadium and Titanium Blast Furnace Smelting Iron Based on Big Data Mining

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Predicting Quantitative Indices for SEN Clogging in Continuous Casting Using Long Short-term Memory Time-series Model

Ruibin Wang, Heng Li, Fernando Guerra, Chad Cathcart, Kinnor Chattopadhyay

pp. 2311-2318

DOI:

10.2355/isijinternational.ISIJINT-2022-181

Abstract

The clogging of submerged entry nozzles is a critical issue during continuous casting that adversely affects final product quality and process productivity. In order to impose effective monitoring and control over the continuous casting process, a quantitative index was formulated to quantify the magnitude of SEN clogging and erosion for a production dataset consisting of ultra-low carbon, low carbon, medium carbon, and calcium treated grades. Three critical index values are defined to represent the clogging event, erosion event, and critical casting condition. Long short-term memory network was established based on the quantitative index in the past four minutes to predict that in the future 48 seconds. The networks are found to be capable of predicting the overall trend in quantitative index, with the lowest normalized root mean squared error at 0.323 for medium carbon grade, followed by that at 0.340, 0.342, and 0.453 for low carbon, calcium-treated carbon, and ultra-low carbon grades respectively. The models can also identify most of the critical casting conditions and erosion incidents for all steel grades. Operators can take corresponding actions when critical conditions are predicted by the models in order to prevent the possible occurrence of clogging. Model precision could be improved with larger production datasets that consist of multiple number of clogging and erosion events.

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Predicting Quantitative Indices for SEN Clogging in Continuous Casting Using Long Short-term Memory Time-series Model

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Visualising Martensite Phase Fraction in Bulk Ferrite Steel by Superimposed Bragg-edge Profile Analysis of Wavelength-resolved Neutron Transmission Imaging

Hirotaka Sato, Atsuya Kusumi, Yoshinori Shiota, Hirotoshi Hayashida, Yuhua Su, Joseph Don Parker, Kenichi Watanabe, Takashi Kamiyama, Yoshiaki Kiyanagi

pp. 2319-2330

DOI:

10.2355/isijinternational.ISIJINT-2022-197

Abstract

Bragg-edge neutron transmission imaging, a wavelength-resolved neutron imaging method, is a unique method for materials characterization. This method can quantitatively visualise various crystalline microstructural information in bulk material over several-centimetres with sub-millimetre spatial resolution. In various forms of crystalline information, the martensite phase fraction in ferritic steel is significant for the characterisation of, e.g., contact surface of an induction-hardened gear, dual phase (DP) steel used for automobiles, and the cutting edge of Japanese swords. However, the martensite phase fraction in a ferrite-martensite steel has not been measured using conventional Bragg-edge analysis methods because the entire neutron transmission spectral pattern of the α’-martensite phase corresponds to that of the α-ferrite phase. However, the Bragg-edge profile of the martensite phase is slightly broader than that of the ferrite phase. For these reasons, we developed a new method for measuring the ferrite/martensite phase fraction from the superimposed Bragg-edge (sBE) profile composed of both sharp α{110} Bragg-edge and broad asymmetric α’{110}-α’{101} Bragg-edge. As a result, two-dimensional imaging and computed tomography of the martensite phase fraction in ferrite-martensite steel were reasonably achieved. In addition, we observed the sBE analysis method to have numerous advantages such as reasonable accuracy (~5%), high precision and stability, and easy handling. Furthermore, we identified the suitability of an asymmetric crystal-lattice-plane-spacing distribution function for the determination of the α’{110}-α’{101} Bragg-edge profile, and found the blurred boundary by mixing unquenched and quenched regions in an induction-hardened steel rod.

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Visualising Martensite Phase Fraction in Bulk Ferrite Steel by Superimposed Bragg-edge Profile Analysis of Wavelength-resolved Neutron Transmission Imaging

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Modeling Transient Jet Impingement Cooling of Moving Hot Steel Plates

Gilles Guedia Guemo, Amir Hossein Nobari, Vladan Prodanovic, Matthias Militzer

pp. 2331-2342

DOI:

10.2355/isijinternational.ISIJINT-2021-457

Abstract

Accelerated cooling (ACC) is one of the key processing steps in the production of Advanced High Performance Steels. In order to obtain thermo-mechanically controlled processed (TMCP) steel products with desired microstructures and mechanical properties, it is necessary to properly adjust the processing parameters of the cooling facility, and therefore it is critically important to quantify the physical process of heat removal by applying water jets on the hot surface of steel. In the present study we propose a mechanistic model for top jet cooling of a moving plate with circular and planar nozzles. The simulation model has been developed based on the extensive experimental database generated with pilot scale runout table tests, and it provides a potentially powerful tool for simulation of cooling of steel strips and plates over the entire length of the cooling facility.

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Modeling Transient Jet Impingement Cooling of Moving Hot Steel Plates

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Effect of Air Temperature on the Thermal Behavior and Mechanical Properties of Wire Rod Steel during Stelmor Cooling

Joong-Ki Hwang

pp. 2343-2354

DOI:

10.2355/isijinternational.ISIJINT-2022-047

Abstract

The effect of air temperature (Ta) on the thermal behavior and mechanical properties of steel wire rods is investigated during the Stelmor air cooling process using a numerical model and an offline cooling simulator. During the Stelmor cooling process, the temperature of the wire rod measured in the summer (28°C) is higher than that in the winter (4°C). The average temperature difference of the wire rod between the seasons is approximately 5°C. In addition, the tensile strength (TS) in the summer is lower than that in the winter: the average TS difference between the seasons is approximately 19 MPa. The different cooling rates of the wire rod depending on Ta are associated with the simple temperature difference between seasons instead of variations in the thermophysical properties of air with temperature. The variation in the cooling rate of the wire rod with Ta is affected significantly by forced convection because the absolute value of the forced convection is approximately 10 times higher than that of natural convection, and the heat flux by thermal radiation is almost unchanged by Ta. The forced convective heat transfer coefficient decreases with Ta because the Reynolds number decreases owing to the decrease in density and increase in kinematic viscosity of air as Ta increases. The deviation in temperature of the wire rod between the summer and winter seasons increases in a wire rod with a small diameter that is fabricated using high forced air because the amount of forced convection increases as the wire diameter decreases and the applied air velocity increases. It is concluded that different working conditions are necessary depending on the Ta, particularly when the wire diameter is small, the blower power is high, and the laying head temperature is high during the Stelmor cooling process.

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ISIJ International Vol.62(2022), No.11

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Effect of Air Temperature on the Thermal Behavior and Mechanical Properties of Wire Rod Steel during Stelmor Cooling

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Enhancement of Mechanical Properties in Dissimilar Resistance Spot Welds between Galvannealed Dual Phase and Al–Si Coated Press Hardening Steels

Zheng Xian Li, Yi Lin Chen, Long Chao Zhang, Raja Devesh Kumar Misra, Hong Ling Yi

pp. 2355-2365

DOI:

10.2355/isijinternational.ISIJINT-2022-123

Abstract

The quality of spot welds between galvanized dual phase steels of 590 MPa (DP590Z) and Al–Si coated press-hardening steels (PHS) of 22MnB5 (PHS1500AS) are determined by welding metallurgy of both base metal and the coating. In this study, extending the dwelling time between two pulses is proposed to suppress splash in the broad process window of welding current and improve mechanical properties of spot welds. The increased welding current enlarges the fusion zone (FZ) size and consequently enhances the strength of welds in both shear and cross tensile tests. Furthermore, martensite with high carbon content and retained austenite near the fusion line was found for the first time in the spot welds in these kinds of steels. The high carbon zone alters the location of broken button and deteriorates the mechanical properties of spot welds. Down-slope pulse is proposed in this study to eliminate carbon enrichment, which improved the mechanical properties of the welds.

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Enhancement of Mechanical Properties in Dissimilar Resistance Spot Welds between Galvannealed Dual Phase and Al–Si Coated Press Hardening Steels

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Identification of Carbides and Phase Transformations in Sintered Fe–Mo–Mn–C Alloys Produced under a Slow Continuous Cooling

Wananurat Srijampan, Amporn Wiengmoon, Arisara Wanalerkngam, Sarum Boonmee, Thanyaporn Yotkaew, Nattaya Tosangthum, Ruangdaj Tongsri

pp. 2366-2373

DOI:

10.2355/isijinternational.ISIJINT-2022-124

Abstract

Different sintered alloys were produced by sintering and slow cooling of powder compacts made from pre-alloyed Fe-0.50Mo-0.15Mn powder mixed with varied graphite powder contents (0.30–1.20 wt.% with 0.15% increment). According to microstructures, sintered alloys were divided into sintered hypo-eutectoid, near eutectoid, and hyper-eutectoid alloys. By using Groesbeck color tinting and X-ray diffraction technique, the common phase transformation products of these sintered alloys were found to include ferrite and carbides. The sintered hypo-eutectoid alloys had microstructures consisting of polygonal ferrite grains and two forms of ferrite + carbide mixtures, such as ferrite + M23C6 carbide and ferrite + M3C carbide. In sintered near-eutectoid alloys, only ferrite + M3C carbide mixtures occupied microstructures. In sintered hyper-eutectoid alloys, large proeutectoid M23C6 carbide formed first and followed by abnormal ferrite, degenerate ferrite + M23C6 pearlite, lamellar ferrite + M23C6 pearlite, Widmanstätten M3C carbide, inverse bainite (ferrite + M3C) and upper bainite (ferrite + M3C).

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Identification of Carbides and Phase Transformations in Sintered Fe–Mo–Mn–C Alloys Produced under a Slow Continuous Cooling

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Effect of High-pressure Quenching on Pure-iron Martensite Transformation and Its Strengthening Mechanism

Qing Cui, Xiaoping Lin, Bin Wen, Shuo Jiang, Hongwang Zhang

pp. 2374-2381

DOI:

10.2355/isijinternational.ISIJINT-2022-167

Abstract

Industrial pure iron samples were austenitized and quenched (6°C/s cooling to room temperature) under hydrostatic pressure of 3–5 GPa. The morphology, phase transformation and strengthening mechanism of high-pressure quenched martensite are analyzed by the method of SEM, XRD, EBSD, and TEM. Lath martensite with hierarchical packet-block-lath structure is induced in industrial pure iron by high pressure, which keeps the Kurdjumov-Sachs (K-S) orientation relationship with the face-center-cubic (FCC) phase. Pressure refines the size of prior austenite by depressing the mobility of grain boundaries, leading to the decrease of the type of martensite variants. with the increment of pressure, the dislocation density increases gradually (2.04×1013 to 3.14×1014 m−2) and the martensite blocks are refined from 3.3 to 0.9 µm. In addition, an enormous number of twin boundaries and high-density dislocations are observed in 5 GPa-samples, which is fairly rare in lath martensite of low carbon steels. Superior tensile performances are obtained in industrial pure iron, especially in 5 GPa-sample with ultra-high yield strength of 700 MPa and excellent ductility of 27%. The strengthening mechanism is quantitatively analyzed by Olson’s strengthening model, and the results show that both of dislocation strengthening and Hall-Petch strengthening enhances with the increase of pressure. Based on the above findings, martensite transformation can be effectively controlled by hydrostatic pressure, which extends the knowledge into martensitic transformation mechanism and offers a new avenue for developing high performance metal materials.

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Effect of High-pressure Quenching on Pure-iron Martensite Transformation and Its Strengthening Mechanism

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Influence of Initial Crystal Orientation and Carbon Content on Rolling-induced Texture in 3 Mass% Si Steel

Yukihiro Shingaki, Minoru Takashima, Yasuyuki Hayakawa

pp. 2382-2388

DOI:

10.2355/isijinternational.ISIJINT-2022-194

Abstract

The influence of the initial crystal orientation and carbon content on rolling-induced texture was investigated using quasi-single crystals of 3.2 mass% Si steel. These specimens had {110}<001> and {110}<113> crystal orientations, which are common near surface textures for hot-rolled steel band. In the case of ultralow-carbon specimens, the initial {110}<001> orientation rotated to {111}<112> after 66% reduction cold rolling and the initial {110}<113> orientation rotated to near {211}<124>. It is considered that the crystal rotation from {110}<113> to near {211}<124> is caused by activation of the {110} slip system, which has the second largest Schmid factor. The {211}<124> orientation is not considered to be a stable rolling-induced texture; however, the {211}<124> orientation was well developed in the present experiments. In addition, the {211}<124> orientation has a geometric characteristic that if it rotates by activation of one slip system, it will revert to the initial {211}<124> crystal orientation by activation of another slip system. In the case of specimens containing carbon, the {110}<001> orientation rotated to {111}<112> and {100}<011> due to deformation twinning. On the other hand, the {110}<113> orientation rotated from the {211}<113> orientation to the {111}<112> orientation during cold rolling. Deformation twinning was also observed. It is considered that the crystal orientation of the deformation twins rotated to near {111}<112> by activation of the {110} slip system.

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Influence of Initial Crystal Orientation and Carbon Content on Rolling-induced Texture in 3 Mass% Si Steel

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Influence of Carbides Precipitated by Low-temperature Tempering on the Room-temperature Mechanical Properties of Grade 91 Steel

Kengo Watanabe, Shuntaro Ida, Kyosuke Yoshimi

pp. 2389-2396

DOI:

10.2355/isijinternational.ISIJINT-2022-213

Abstract

The precipitation behavior of carbides in modified 9Cr-1Mo steel (Grade 91) subjected to low-temperature tempering and the influence of those carbides on the mechanical properties at room temperature were investigated. An as-quenched sample (AQ) contained a small amount of metal carbide (MC) in its martensite microstructure. On low-temperature tempering at 300–500°C, intended to suppress the recovery and growth of the dislocation substructure, three types of carbide were formed; these were identified as Fe4C, hP8-type Fe3C, and oP16-type Fe3C by using replica samples for transmission electron microscopy and extracted-residue analyses. Samples subjected to double low-temperature tempering at 500°C for 5 min and then at 300°C for 1 h (DLTT) contained large amounts of carbide compared with the AQ sample, but had similar a lath width. The hardness of the DLTT sample was higher than that of the AQ sample, whereas its tensile strength was slightly lower than that of the AQ sample, regardless of the strain rate. The reason that precipitation strengthening did not increase tensile strength is considered to be the early formation of microvoids due to delamination at the carbide/matrix interfaces during tensile testing.

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Influence of Carbides Precipitated by Low-temperature Tempering on the Room-temperature Mechanical Properties of Grade 91 Steel

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Hardening of 80CrV2 in Bladesmith Forge

Juha Perttula

pp. 2397-2401

DOI:

10.2355/isijinternational.ISIJINT-2022-245

Abstract

Some bladesmiths have started to use 80CrV2 because V alloying helps with grain size. Smiths usually forge blades from unalloyed high carbon steels, but if Al deoxidation is not used, they are prone to grain growth. This work studies the forge hardening of 80CrV2 and C75 in the absence of Al. Specimens were heated in a gas-fired forge and austenitization was detected with a magnet. Both steel grades hardened when quenched after the disappearance of magnetism, but 80CrV2, due to Cr alloying, needed about 60°C higher temperature to attain maximum hardness. Grain growth did not start in 80CrV2 despite some overheating, while in C75 it started immediately after austenitization. The tests show that 80CrV2 attains easily good mechanical properties in forge hardening.

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Hardening of 80CrV2 in Bladesmith Forge

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Hydrogen Effect on the Mobility of Edge Dislocation in α-Iron: A Long-Timescale Molecular Dynamics Simulation

Ryosuke Matsumoto, Sunday T. Oyinbo, Mugilgeethan Vijendran, Shinya Taketomi

pp. 2402-2409

DOI:

10.2355/isijinternational.ISIJINT-2022-311

Abstract

Explaining the hydrogen effect on dislocation mobility is crucial to revealing the mechanisms of hydrogen-related fracture phenomena. According to the general perspective, reducing the speed of dislocation can give enough time to hydrogen to catch up with the dislocation migration. In this research, we conducted molecular dynamics (MD) simulations to investigate the impact of hydrogen on the edge-dislocation motion in α-iron at various dislocation speeds and temperatures. It was discovered that, for all hydrogen concentrations evaluated in this paper, the hydrogen effect on dislocation transition from pinning to dragging occurs at a dislocation speed of around 0.1 m/s at 300 K. When the dislocation velocity is reduced to 0.01 m/s employing long timescale MD simulations over 1 µs, it is observed that hydrogen follows dislocation motion with small jumps in the dislocation core. The required stress to migrate the edge dislocation at a speed of 0.01 m/s was discovered to be 400 MPa, even at a lower hydrogen concentration, which was achieved in a gaseous hydrogen environment with lower pressure than atmospheric pressure. Although the dislocation still traps hydrogen at 500 K, as temperature increases, the impact of hydrogen on the shear stress required for dislocation glide becomes negligibly small. The required shear stress at lower dislocation speeds was predicted by employing the stress-dependent thermal activation model assuming the hydrogen diffusion rate-determining. The finding demonstrated that the edge dislocation should slow down until 1 mm/s order or less in the presence of hydrogen and suitable stress for α-iron.

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Hydrogen Effect on the Mobility of Edge Dislocation in α-Iron: A Long-Timescale Molecular Dynamics Simulation

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Effect of Rare Earth Elements on Microstructure and Hot Workability of AISI T15 High Speed Steel

Bo Zhao, Min Xia, Jun-Feng Wang, Chang-Chun Ge

pp. 2410-2420

DOI:

10.2355/isijinternational.ISIJINT-2021-442

Abstract

To investigate the effect of rare earth elements (REEs) on hot workability and the microstructure evolution of AISI T15 high-speed steel (HSS), hot compression tests were conducted using a Gleeble-1500D thermal simulation machine at the temperature of 1000–1150°C and the strain rate of 0.01–10 s−1. The experimental results show that the flow stress of the modified samples by REEs is lower than that of REEs-free samples under the same conditions, indicating that REEs cause a reduction in deformation resistance (stress level) and improve the deformability of the as-cast high alloy steels at elevated temperatures. A hyperbolic-sine function was adopted to characterize the flow stress as a function of deformation temperature and strain rate and the apparent activation energy of T15 HSS before and after adding REEs were determined to be approximately 557.3 kJ/mol and 513.97 kJ/mol, respectively. Therefore, it is inferred that REEs are beneficial to the occurrence of dynamic recrystallization (DRX), which has also been demonstrated through the determination of characteristic points on the stress-strain curves and the evolution of microstructure. The metallographic analysis also indicates that REEs refine the recrystallized grains and eutectic carbide network and make the deformed microstructure more uniform. Additionally, the maps of power dissipation and instability based on the Dynamic Materials Modeling approach (DMM) were established to evaluate the effect of REEs on hot workability.

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Effect of Rare Earth Elements on Microstructure and Hot Workability of AISI T15 High Speed Steel

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Corrections of the figure in the paper “Effect of Cerium and Magnesium Addition on Evolution and Particle Size of Inclusions in Al-killed Molten Steel” [ISIJ International, Vol. 62 (2022), No. 9, pp. 1852-1861]

Yeguang Wang, Chengjun Liu

pp. 2421-2421

DOI:

10.2355/isijinternational.62.2421

Abstract

DOI: https://doi.org/10.2355/isijinternational.ISIJINT-2022-104 The authors have found that the Figures 13(b) reported in the above paper is incorrect. Figures 13 should be replaced by the following figure: Fig. 13.Morphology and elemental mapping of inclusions after the in-situ observation (a) CeAlO3 inclusion cluster, (b) MgO-Al2O3 inclusions after Mg treatment, (c) Ce2O3-Al2O3-MgO complex inclusion after Mg treatment. (Online version in color.) These corrections do not affect main results, discussion and conclusions in the article at all. The authors deeply apologize for causing the readers inconvenience by this mistake.

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Corrections of the figure in the paper “Effect of Cerium and Magnesium Addition on Evolution and Particle Size of Inclusions in Al-killed Molten Steel” [ISIJ International, Vol. 62 (2022), No. 9, pp. 1852-1861]

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ISIJ International Vol.62(2022), No.11

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