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ISIJ International Advance Publication

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)

    1. No.13
    2. No.12
    3. No.11
    4. No.10
    5. No.9
    6. No.8
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  2. Vol. 63 (2023)

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  3. Vol. 62 (2022)

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  4. Vol. 61 (2021)

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  5. Vol. 60 (2020)

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  6. Vol. 59 (2019)

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  7. Vol. 58 (2018)

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  8. Vol. 57 (2017)

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  9. Vol. 56 (2016)

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  10. Vol. 55 (2015)

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  11. Vol. 54 (2014)

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  12. Vol. 53 (2013)

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  13. Vol. 52 (2012)

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  14. Vol. 51 (2011)

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  15. Vol. 50 (2010)

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  16. Vol. 49 (2009)

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  17. Vol. 48 (2008)

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  18. Vol. 47 (2007)

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  19. Vol. 46 (2006)

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  20. Vol. 45 (2005)

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  21. Vol. 44 (2004)

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  22. Vol. 43 (2003)

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  23. Vol. 42 (2002)

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  24. Vol. 41 (2001)

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  25. Vol. 40 (2000)

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  26. Vol. 39 (1999)

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  27. Vol. 38 (1998)

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  28. Vol. 37 (1997)

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  29. Vol. 36 (1996)

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  30. Vol. 35 (1995)

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  31. Vol. 34 (1994)

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  32. Vol. 33 (1993)

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  33. Vol. 32 (1992)

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  34. Vol. 31 (1991)

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  35. Vol. 30 (1990)

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  36. Vol. 29 (1989)

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21 Nov. (Last 30 Days)

ISIJ International Advance Publication

SOKD: A soft optimization knowledge distillation scheme for surface defects identification of hot-rolled strip

Wenyan Wang, Zheng Ren, Cheng Wang, Kun Lu, Tao Tao, Xuejuan Pan, Bing Wang

DOI:

10.2355/isijinternational.ISIJINT-2024-159

Abstract

The surface defect of hot-rolled strip is a significant factor that impacts the performance of strip products. In recent years, convolutional neural networks (CNNs) have been extensively used in strip surface defect recognition to ensure product quality. However, the existing CNNs-based methods confront the challenges of high complexity, difficult deployment and slow inference speed. Accordingly, this work proposes a soft optimization knowledge distillation (SOKD) scheme to distill the ResNet-152 large model and extract a compact strip surface recognition model. The SOKD scheme utilizes Kullback-Leibler (KL) divergence to minimize the error between the soft probability distributions of the student network and the teacher network, and gradually reduces the weight of "Hard loss" during the training process. The operation significantly reduces the learning constraints that the prior knowledge of the teacher network on the student network in the original KD, which improves the recognition performance of the model. Additionally, SOKD is applicable to most CNNs for identify surface defect of hot-rolled strip. The experimental results on NEU-CLS dataset show that the SOKD outperforms state-of-the-art methods.

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Evolution and Influence of Flow Field Affected by Coupled Swirling Flows in Round Billet Mold

Chunlei Wu, Yanwen Sun, Zhexiao Liu, Qiang Wang, Xiaoming Liu, Dewei Li, Xiaowei Zhu, Chunyang Shi

DOI:

10.2355/isijinternational.ISIJINT-2024-252

Abstract

The quality of round billet is affected by the flow characteristics of molten steel during continuous casting. The application of nozzle swirling flow combined with electromagnetic stirrer (M-EMS) can increase the number of equiaxed crystal and alleviate macrosegregation, which has been demonstrated in our previous industrial test. However, flow field cannot be visually observed in industrial tests. In this paper, for the first time, the evolution of flow field and its influence on the macrosegregation and liquid level fluctuation under the action of coupled swirling flows were studied. Compared with that by using only mold stirring, the flow field was distributed more symmetrically in the upper part of mold and its impact depth decreased from 350 mm to 246 mm when the rotating speed of stirring propeller was 70 r/min. The centerline segregation level was reduced owing to the inward flow weakened by the outward nozzle swirling flow. Additionally, the tangential velocity at 1/2 radius near the surface was decreased from 0.589 m/s to 0.469 m/s, leading to the reduction of liquid level fluctuation. Consequently, both the internal quality and the surface quality can be improved by coupled swirling flows, provided that the rotating intensities of nozzle swirling flow and M-EMS are selected properly in the actual continuous casting production.

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Evolution and Influence of Flow Field Affected by Coupled Swirling Flows in Round Billet Mold

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A volume expansion kinetic model of decarburization of liquid Fe-1wt%C alloy by Ar-CO2 blowing

Junho Lee, Yongsug Chung

DOI:

10.2355/isijinternational.ISIJINT-2024-167

Abstract

The decarburization kinetics according to the Ar-CO2 ratio with a liquid Fe-1wt%C alloy was studied using a high-frequency induction furnace at 1873K. The carbon content in the liquid alloy decreased linearly with time, and as the CO2 ratio increased, the decarburization rate of the liquid alloy increased. The main reaction turned out to be CO2 + C = 2CO based on thermodynamic calculation. Comparing the amount of CO2 gas blown into the liquid alloy and the carbon content in the liquid alloy, it was found that all CO2 gas reacted with dissolved carbon when present as bubbles. A volume expansion model is proposed that takes into account the change in the partial pressure of gases due to the decarburization reaction and the resulting volume expansion of gases. Upon applying this model when S was low (50 ppm) and when S was high (0.1wt%), no differences were found in the three possible rate-controlling steps (gas phase mass transfer, dissociation&adsorption, and mixed control) when S was low, but Mixed control behavior was observed when S was high.

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A volume expansion kinetic model of decarburization of liquid Fe-1wt%C alloy by Ar-CO2 blowing

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Effects of quasi-particles structure on the combustion behaviors and CO and NO emissions in the iron ore sintering

Tao Han, Changqing Hu, Xuefeng Shi, Yan Shi

DOI:

10.2355/isijinternational.ISIJINT-2024-236

Abstract

To investigate the influences of quasi-particles structure in the sintering bed on combustion behaviors and CO and NO emission, the non-isothermal combustion experiments and gas analysis were carried out by using coke breeze and sintering raw materials to prepare different types of quasi-particles. The results show that the four types of quasi-particles combustion processes were consistent with the unreacted nuclei model. The adhering layer had positive catalytic effects on coke breeze combustion and the reduction of NO by CO. Compared with S´-0.25, the apparent activation energies of the C71% and P15%(2) combustion decreased by 1.85 kJ/mol and 27.34 kJ/mol, the CO emission reductions were 47.75% and 50.07%, and the NO emissions were reduced by 67.50% and 6.95%, respectively. Compared with S´2~3, the apparent activation energies of the S33%(2~3) decreased by 18.66 kJ/mol, and the emissions of CO and NO were decreased by 87.99% and 75.29%, respectively. Additionally, the structural changes of the four types of quasi-particles significantly affected the combustion and emission behaviors. The adhering fines of S-type, C-type and P-type had abundant porous structure, which provided active sites for the adsorption of CO and NO, promoted the reduction of NO by CO. In contrast, the emissions of S´-type gases were higher, and the emissions increased with increasing of size. Therefore, increasing the S-type content and reducing the S´-type content in the sintering bed will not only effectively improve the solid fuel combustion efficiency, ensure sufficient combustion zone temperature, but also greatly reduce emissions in the sintering flue gas.

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Effects of quasi-particles structure on the combustion behaviors and CO and NO emissions in the iron ore sintering

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Plasma Nitriding of Austenitic Stainless Steel using Ti-Mo Combination Screen

Yasuhiro Hoshiyama, Yuki Furuta, Tomoki Maruoka

DOI:

10.2355/isijinternational.ISIJINT-2024-251

Abstract

Austenitic stainless steels such as SUS304 are widely used in various applications due to their excellent corrosion resistance; however, their low hardness and wear resistance limit their structural use. Plasma nitriding was applied using a Ti-Mo combination screen to simultaneously form a Ti-Mo composite nitride layer and a nitrogen diffusion layer in SUS304 stainless steel. The microstructure and mechanical properties of the plasma-nitrided SUS304 were evaluated. XRD analysis revealed peaks of δ-(Ti,Mo)N, which originated from the constituent elements of the screen, indicating the successful formation of a Ti-Mo-N composite nitride layer on the sample surface. The thickness of the Ti-Mo-N layer increased with higher gas pressure and nitrogen content in the gas mixture. The formation of the Ti-Mo-N layer on the nitrogen diffusion layer significantly enhanced the hardness and reduced the kinetic friction coefficient. The results suggest that this surface treatment method could be beneficial for improving the durability and lifespan of stainless steel components in demanding applications.

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Plasma Nitriding of Austenitic Stainless Steel using Ti-Mo Combination Screen

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Molecular dynamics simulation of viscosity of the CaO, MgO and Al2O3 melts

Alexander Moiseev, Alex Kondratiev

DOI:

10.2355/isijinternational.ISIJINT-2024-263

Abstract

Viscosity of oxide melts is a fundamental physicochemical property that plays a critical role in important technological and natural processes like slag flow, slag/metal separation, volcano eruptions etc. Unfortunately, many oxides melt at extremely high temperatures and are highly corrosive in the liquid state, which makes experimental measurement of viscosity by conventional experimental techniques a difficult, expensive, and sometimes impossible task. In this case it might be helpful to use other methods to determine viscosity, such as modelling or simulation. In the present paper the shear viscosity coefficients of the liquid CaO, MgO, and Al2O3 have been simulated via the classical molecular dynamics and compared to the available viscosity data (e.g. experimental viscosities, other model predictions) collected and stored in a databank by one of the authors. Different viscosity calculation techniques (e.g. the Green-Kubo equation, the Einstein relation, and the non-equilibrium molecular dynamics methods) coupled with MD have been employed to ensure a more reliable viscosity calculation. It has been shown that the simulated viscosities of the CaO and MgO melts are close to those calculated by phenomenological viscosity models and represent a plausible estimation for viscosity of these unary systems. It has also been shown that the simulated viscosity of the Al2O3 melt is lower than the majority of the available experimental data. In general, it has been demonstrated that the molecular dynamics simulation could provide a reasonable estimation of viscosity, especially if no other viscosity data is available.

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Molecular dynamics simulation of viscosity of the CaO, MgO and Al2O3 melts

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Creep rupture strength and phase stability of the austenite phase for KA-SUS304J1HTB

Yoshiki Shioda, Noriko Saito, Kyohei Nomura, Keiji Kubushiro

DOI:

10.2355/isijinternational.ISIJINT-2024-264

Abstract

Metallurgical factor causing the heat-to-heat variation in creep rupture strength have been investigated for KA-SUS304J1HTB. In the long-term, there was a maximum difference of 3.5 times in creep rupture time between the heat with low creep strength and the heat with high creep strength. In the heat with low creep rupture strength, most of the creep voids occurred at the matrix/σ phase interface. Moreover, in the heat with low creep rupture strength, the area fraction of σ phase was larger than in the heat with high creep rupture strength. Considering that the difference in the area fraction of σ phase in each heat is related to the difference in phase stability of the austenite phase, the Md—— value in each heat was evaluated. The Md—— value is the parameter correlated with phase stability. The creep rupture time of each heat was correlated with the Md—— value. The smaller the Md—— value, the longer the creep rupture time. Therefore, the heat-to-heat variation in creep rupture strength is caused by the difference in the phase stability of each heat. In other words, in the heats with low phase stability, creep rupture strength is low because a large amount of σ phase precipitates during the creep test.

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Creep rupture strength and phase stability of the austenite phase for KA-SUS304J1HTB

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Injection of hydrogenous gases into the blast furnace tuyeres for reducing CO2 emissions: a review

Volodymyr Shatokha

DOI:

10.2355/isijinternational.ISIJINT-2024-145

Abstract

Transitioning to alternative fuels like natural gas (NG), coke oven gas (COG), or hydrogen presents a viable path to reduce carbon emissions in blast furnace ironmaking. A review of industrial practices and simulations reveals significant variabilities in estimating the impacts of hydrogenous gases' tuyere injection on the blast furnace operation due to a lack of representative industrial-scale experiments and diverse modeling approaches. NG is effective yet regionally constrained, while COG, although beneficial for improving efficiency and reducing emissions, has limited availability for injection. High coke replacement efficiency ranks NG superior for emission reduction. Meanwhile, COG and cold hydrogen offer similar CO2 reduction potentials, with carbonaceous gases offsetting COG's higher coke replacement ratio. Preheating hydrogen can further improve its coke replacement efficacy, achieving the greatest reduction in CO2 emissions. Hydrogen injection has yet to reach economic viability, but technological progress, scaling up, and evolving carbon legislation could alter this, prompting steel producers worldwide to advance hydrogen injection techniques in blast furnaces.

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Injection of hydrogenous gases into the blast furnace tuyeres for reducing CO2 emissions: a review

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Terminal Settling Velocity of Particle in Suspension

Shin’ichi Shimasaki, Shigeru Ueda, Noritaka Saito

DOI:

10.2355/isijinternational.ISIJINT-2024-269

Abstract

In the steelmaking process, most slags and fluxes often contain a solid phase, such as CaO. The suspension in which solid phases are suspended has higher viscosity than that of a pure matrix liquid. Therefore, it is expected that the viscosity of slag containing solid phases will increase. In this study, the terminal settling velocity of particles in a suspension has been measured. The suspensions consist of a silicone oil matrix and polyethylene beads, and the settling particles are bearing balls made of stainless steel. As a result of the higher viscosity of suspension, the terminal settling velocity of the bearing ball becomes slower than that in the pure silicone oil. It was clarified that the retardation of the terminal velocity and the increase in the drag coefficient depend only on the volume fraction of the solid phase (polyethylene beads) of the suspension, and they are independent of the size of the suspended beads and the viscosity of the matrix liquid. A correlation equation for predicting the drag coefficient of particles in a suspension was proposed.

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Terminal Settling Velocity of Particle in Suspension

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Reduction and Carburization Behaviors of Iron Oxide Composite with Iron Carbide and Free Carbon

Ryota Higashi, Daisuke Maruoka, Yuji Iwami, Taichi Murakami

DOI:

10.2355/isijinternational.ISIJINT-2024-271

Abstract

The blast furnace ironmaking process relies heavily on fossil fuels, posing challenges to achieving carbon neutrality. New methods, like hydrogen reduction ironmaking, face limitations such as the need for high-grade iron ore and issues with DRI melting. To address these, biomass char has been explored as a carbon-neutral carburizing agent, yet practical application is difficult due to biomass supply limitations in East Asia. Thus, Carbon Capture and Utilization, CCU becomes essential. Examples include iACRES and carbon recycling blast furnaces, which recycle CO2 for reducing agents but have limited scope.

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Reduction and Carburization Behaviors of Iron Oxide Composite with Iron Carbide and Free Carbon

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Integrated experimental phase equilibria and thermodynamic modelling investigation of the FeO–Fe2O3–MgO and the FeO–Fe2O3–MgO–SiO2 systems. Part I: Experimental results in air

Igor Babaian, Maksym Shevchenko, Evgenii Nekhoroshev, Evgueni Jak

DOI:

10.2355/isijinternational.ISIJINT-2024-280

Abstract

Phase equilibria studies were undertaken on the FeO- Fe2O3 – MgO-SiO2 and FeO -Fe2O3- MgO systems in air using an equilibration and quenching technique. Concentrations of Fe, Mg, Si in the coexisting phases were measured using electron probe X-ray microanalysis (EPMA) with a wavelength dispersive spectrometer (WDS) detector. The liquidus temperatures have been determined from 1400 °C to 1740 °C in primary phase fields of spinel, monoxide, olivine, pyroxene, tridymite, cristobalite and in two-liquids miscibility gap. Tielines between co-existing phases and the compositions of solid solutions have been determined. In the absence of a liquid phase which would facilitate mass transport, the subsolidus phase relations in the Fe2O3- MgO system were not studied directly. The measurements in the low-SiO2 area of pseudo-ternary "Fe2O3" - MgO-SiO2 system were used to derive phase equilibria of the "Fe2O3" -MgO pseudo-binary system with a special focus on the monoxide-spinel phase boundary. The present study is a part of the research program on the characterization of the MgO-containing refractory systems within the multicomponent Pb-Zn-Cu-Fe-Ca-Si-O-S-Al-Mg-Cr-Na-As-Sn-Sb-Bi-Ag-Au-Ni-Co system.

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Integrated experimental phase equilibria and thermodynamic modelling investigation of the FeO–Fe2O3–MgO and the FeO–Fe2O3–MgO–SiO2 systems. Part I: Experimental results in air

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In-situ Observation of Precipitation and Growth of MnS Inclusions during Solidification of a High Sulfur Steel

Haixin Yang, Ying Ren, Jinshu Wang, Lifeng Zhang

DOI:

10.2355/isijinternational.ISIJINT-2024-195

Abstract

The effect of the cooling rate on the morphology, number density, and size distribution of MnS inclusions in a high sulfur steel was investigated. With the increase of the cooling rate from 15 K/min to 300 K/min, the number density of MnS inclusions ranged from 91 #/mm2 to 192 #/mm2, and the average size of MnS inclusions decreased from 7.4 μm to 5.3 μm. A coupled model was developed to predict the precipitation and growth of MnS inclusions. The precipitation temperature of MnS at different cooling rates was approximately 1823 K, which agreed well with experimental results. Through the high-temperature confocal scanning laser microscope, the precipitation process of MnS in a high sulfur steel during the solidification was observed. Inclusions of MnS primarily precipitated at grain boundaries, while the morphology of MnS before and after solidification was influenced by the cooling rate. A higher cooling rate promoted elongated MnS inclusions precipitated, and smaller MnS particles were precipitated after solidification. Conversely, a slower cooling rate led to the massive MnS inclusions precipitated during solidification, leading to the formation of elongated MnS particles.

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In-situ Observation of Precipitation and Growth of MnS Inclusions during Solidification of a High Sulfur Steel

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Measurement of Bubble Size Distribution and Generation Position of Bubbles Generated during Smelting Reduction of Iron Oxide-containing Slag

Ko-ichiro Ohno, Taiga Eguchi, Tatsuya Kon

DOI:

10.2355/isijinternational.ISIJINT-2024-262

Abstract

Slag foaming is a phenomenon caused by the generation of CO bubbles due to the reaction between iron oxide in slag and carbon in pig iron. The purpose of this study is to explore the controlling factors of slag foaming by observing the bubble formation behavior caused by the chemical reaction between iron oxide and Fe-C alloy in slag. 0.06 g of Fe-C alloy was charged to the bottom of the BN crucible, and 6.0 g of slag (SiO2:CaO:Fe2O3 = 40:40:30) was charged on top of it. The crucible was placed in an infrared image heating furnace, and the temperature was rapidly raised to 1370°C at a rate of 1000°C/min in a N2 stream, then held for a predetermined time and rapidly cooled. After rapidly cooling, the internal structure of the sample was observed using a high-resolution X-ray CT device. The spherical equivalent volume is calculated based on the number of bubbles observed and their equivalent circle diameter, and the relationship between the volume ratio of small bubbles in the slag volume and the distance from the bottom of the crucible is calculated, and the bubble density and volume ratio are calculated. It was suggested that the value tends to increase as the distance from the bottom of the crucible increases.

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Measurement of Bubble Size Distribution and Generation Position of Bubbles Generated during Smelting Reduction of Iron Oxide-containing Slag

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Phase equilibria of the iron-rich corner of the CaO-Fe2O3-Al2O3 system at 1240 °C in air

Hirokazu Sato, Maksym Shevchenko, Kazumasa Sugiyama, Siyu Cheng, Jiang Chen, Peter Charles Hayes, Evgueni Jak, Miyuki Hayashi

DOI:

10.2355/isijinternational.ISIJINT-2024-260

Abstract

The compositional ranges of SFCA-I and other SFCA series and the phase equilibrium relationships were investigated in the iron-rich corner of the CaO-Fe2O3-Al2O3 system at 1240 °C in air using powder and single crystal XRD as well as EPMA. To obtain the desired composition, reagent-grade CaCO3, Fe2O3, and Al2O3 powders were weighed, mixed, and equilibrated at 1240oC in air. Each of the obtained samples was divided into two parts: one was pulverized into a powder and analyzed by XRD, and the other was subjected to microstructural observation and compositional analysis using EPMA. The crystalline structures of the SFCA series for some samples were analyzed by a single XRD. The results revealed that not only SFCA-I but also SFCA-II and SFCA have been found in the compositional area of this study; the Al/(Al+Ca+Fe) concentration ranges are 7.89–20.33 mol% for SFCA-I, 17.62–24.55 mol% for SFCA-II and 20.93–27.60 mol% or even higher for SFCA. The compositions of SFCA are on the line satisfying M14O20, while those of SFCA-I and SFCA-II deviate from the lines satisfying M20O28 and M17O24, respectively, and are closer to the line satisfying M14O20. Since the compositions were derived based on the assumption that all Fe irons are Fe3+, the apparent compositions of SFCA-I and SFCA-II deviate from M20O28 and M17O24, respectively, owing to the presence of trace amounts of Fe2+.

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Phase equilibria of the iron-rich corner of the CaO-Fe2O3-Al2O3 system at 1240 °C in air

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Sampling Strategy of Bubble Characteristics in a 1:2 Scale Curved Continuous Casting Mold: Parametric and Prediction Study

Soumitra Kumar Dinda, Donghui Li, Fernando Guerra, Chad Cathcart, Mansoor Barati

DOI:

10.2355/isijinternational.ISIJINT-2024-081

Abstract

Argon gas injection in slab continuous casting is common practice to counter SEN clogging phenomena. Bubble characteristics determine the probability of bubble-driven defects such as steel cleanliness, liquid steel reoxidation, and sliver and blister defects. 1:2 scaled water model studies were performed with the help of an advanced high-speed-high-resolution camera shadowgraph imaging technique. Bubble Sauter mean diameter and count were calculated using Trainable Weka segmentation, a machine learning image-based segmentation in the ImageJ platform for different processing conditions such as gas flow rate, liquid flow rate, mold width, and submerged entry nozzle (SEN) depth. A predictive model was developed on the experimental data using an artificial neural network (ANN) algorithm to optimize the bubble mean diameter and count sampling strategy. The model performance is optimized based on the cross-validated adjusted R2. The model shows significant promise with bootstrapping aggregation, five-fold cross-validation, and improved accuracy.

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Sampling Strategy of Bubble Characteristics in a 1:2 Scale Curved Continuous Casting Mold: Parametric and Prediction Study

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Compressive strength and thermal properties of ferro coke prepared by cold pressing method

Yanhui Li, Fei Liao, Rui Guo, Huan Cheng, Zhang Sun, Zhennan Gao, Liangyuan Hao

DOI:

10.2355/isijinternational.ISIJINT-2024-295

Abstract

This research aimed to investigate the production of ferro coke with high strength by cold pressing without adding binder, to meet the requirements of the metallurgical industry and avoid the environmental pollution problems caused by the hot pressing process. The effects of pressure and proportion of iron ore powder on the preparation of ferro coke from a weakly caking coal and a strongly caking coal were studied. The results show that when no binder is added, the ferro coke made from weakly caking coal has the highest compressive strength of 5.13 KN, while the ferro coke made from strongly caking coal has the highest compressive strength of 4.93 KN.

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Compressive strength and thermal properties of ferro coke prepared by cold pressing method

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Artificial neural network model for estimating mold flux melting temperature

Carlo Mapelli, Davide Mombelli, Gianluca Dall’osto, Jung-Wook Cho, Nathalie Gruber, Irmtraud Marschall, Maïté Cornille, Marco Alloni, Riccardo Carli

DOI:

10.2355/isijinternational.ISIJINT-2024-151

Abstract

The accuracy of the current models for the calculation of the melting temperature of the mold flux shows that there is still room for improvement, given that their accuracy could not be satisfactory enough to keep up with the current industrial needs. In this work the use of artificial neural networks for data prediction is explored. The network acts as a "black box" capable to predict the melting temperature determined by complex physical interaction among the involved chemical species composing the flux. The network is trained by learning from real experimental data provided by different research groups through hot stage microscopy. The data was tested first within its respective batches and then tested as a single aggregate data batch. After testing and optimization of the networks' parameters, an acceptable level of accuracy was reached because the estimated melting temperatures point out an average error lower than 30 K if compared to measured data. This opens the possibility for the development of a standalone application that can be used for reference. In order to open the possibility for further improvements of this study the paper shares and makes public the values contained in the matrixes connecting the nodes of neural networks.

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Artificial neural network model for estimating mold flux melting temperature

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Viscosity Measurement of CaO-SiO2-FexO Foaming Slag at 1673 K

Yoshiyuki Egashira, Noritaka Saito, Kunihiko Nakashima

DOI:

10.2355/isijinternational.ISIJINT-2024-222

Abstract

Foaming slag generated in the steelmaking process, especially in hot-metal pretreatment and electric arc furnaces, is a gas-liquid coexistent fluid with CO gas generated by the interfacial reaction between slag containing iron oxide and hot metal or carbonaceous materials. In addition, it is essential to understand the flow behavior of foaming slag during slag-tapping and the sedimentation behavior of iron particles, which affects iron yield, and to expand our knowledge of the viscosity of gas-liquid coexisting fluids for CFD modeling of these phenomena. In the present study, the apparent viscosity of a foaming slag was systematically investigated, which was generated by reacting CaO-SiO2-FexO slag with Fe-C alloy and varying the composition, gas phase ratio, and shear rate of the slag. By adding Fe-C alloy powder to the slag, bubbles were continuously generated in the molten slag, and foaming slag suitable for viscosity measurement could be prepared. It was found that the higher the amount of Fe-C alloy powder, the larger the gas phase ratio of the foaming slag due to an increase in the number of bubbles generated. The relative viscosity of the foaming slag was found to increase with the gas phase ratio. The higher the rotation speed, the smaller the relative viscosity of the foaming slag indicating shear-thinning characteristics. The relationship between shear rate and shear stress calculated from the viscosity of the foaming slag did not show general non-Newtonian fluid behavior.

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Viscosity Measurement of CaO-SiO2-FexO Foaming Slag at 1673 K

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Effect of Iron Oxide on Sulfide Capacities of CaO-SiO2-FeO and CaO-Al2O3-FeO Ternary Systems

Masakatsu Hasegawa, Keijiro Saito, Kosuke Awaya, Domu Mitsuyama

DOI:

10.2355/isijinternational.ISIJINT-2024-267

Abstract

Towards steelmaking processes which are compatible with the sustainable society, re-sulfurization reaction in hot metal pre-treatments needs to be suppressed as much as possible. To evaluate the effects of iron oxide on the sulfur distribution ratio between FeO-containing slag and hot metal, sulfide capacities and FeO activities were measured in CaO-SiO2-FeO and CaO-Al2O3-FeO ternary liquid slags. Although the FeO activity and oxygen potential increased, the addition of FeO raised sulfide capacity drastically and resulted in an increase in the calculated value for distribution ratio of sulfur.

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Effect of Iron Oxide on Sulfide Capacities of CaO-SiO2-FeO and CaO-Al2O3-FeO Ternary Systems

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Application of pellet sintering in manganese ore fines and its consolidation behavior

Wei Liu, Deqing Zhu, Jian Pan, Zhenning Wei, Zhengqi Guo, Congcong Yang, Siwei Li

DOI:

10.2355/isijinternational.ISIJINT-2024-187

Abstract

The high solid fuel consumption has been a persistent problem for Steel production mills during the sintering process of manganese ore fines. This manuscript adopts the method of pellet-sintering to process manganese ore fines, and investigates the optimization of the sintering parameters for manganese ore fines, as well as its agglomeration mechanism. The sintering pot tests shown that the pellet-sintering required about 3.5% coke breeze dosage significantly lower than the traditional sintering (about 5%~10%), while the sintering indices can be achieved a yield of 71.12%, a tumble index of 62.48%, a solid fuel consumption of 55.87kg/t, and a productivity of 1.29 t·h-1·m-2 under the condition of pellet size is 8~12mm. XRD and SEM-EDS analyses indicated that the major mineral phases of sinter products included hausmannite (Mn3O4), ferrotephroite [(Fe,Mn)2SiO4], Fe-Mn oxides (FexMn3-xO4), bustamite [(Mn,Fe,Ca)·5(Si5O15)], rich-Mn bearing silicate melts and a small quantity of free quartz (SiO2). Optical microstructure and SEM images showed that hausmannite and Fe-Mn oxides are in blocky, with crystal-to-crystal bridging connections. ferrotephroite is rodlike, with a small amount appearing skeletal. The well-developed crystals are intertwined and closely interconnected, greatly enhancing the quality of the sinter product.

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Application of pellet sintering in manganese ore fines and its consolidation behavior

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Effect of the injection position on mixing time in a centric gas-stirred ladle water model assisted by a systematic CFD study

Rodrigo Villarreal-Medina, Luis E. Jardón-Pérez, Adrián M. Amaro-Villeda, Gerardo Trápaga, Marco A. Ramírez-Argáez

DOI:

10.2355/isijinternational.ISIJINT-2024-201

Abstract

Mixing time is a parameter that describes the degree of agitation in a gas-stirred ladle. The literature is not conclusive on the effect of the tracer injection position on the mixing time under equal stirring conditions. This work conducted a systematic and comprehensive study on the effect of the tracer position on the mixing time for centric injection. Results in the form of a mixing time map indicate that the diagonal formed between the inlet and the upper wall region gets the fastest mixing, and specifically in the eye of the toroid of the circulation loop is the best position to mix solute rapidly. In contrast, the dead zones at the lower near-wall part of the ladle have the poorest mixing behavior for the tracer addition. The study also tested the ladle's axisymmetric assumption since two points were at different angular positions, but the same axial and radial points presented similar mixing time.

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Effect of the injection position on mixing time in a centric gas-stirred ladle water model assisted by a systematic CFD study

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Chemical and Mechanical Factors on Phosphorus Dissolution Behavior from P-concentrated Slag

Takayuki Iwama, Ryo Inoue, Kenji Nakase, Shigeru Ueda

DOI:

10.2355/isijinternational.ISIJINT-2024-234

Abstract

Since it has been urgently demanded to secure the secondary phosphorus resources domestically in addition to the establishment of a stable supplying path of phosphate ore from overseas, the recovery of phosphorus from steelmaking slags is attracting attention. The phosphorus-enriched slag obtained by dephosphorizing the high phosphorus hot metal, which was prepared by the reduction of conventional steelmaking slag, is thought to be useful as a raw phosphorus resource. It was reported in our previous paper that phosphorus can be effectively separated from P-enriched slag by the citric acid leaching method. In this study, the effects of citric acid concentration in solution, solution temperature, slag/solution mass ratio, and P-enriched slag composition on phosphorus dissolution behavior were additively investigated. A phosphorus dissolution from the P-enriched slag was significantly promoted by increasing the citric acid concentration in solution. However, even if the solution temperature was increased during leaching, the speed and ratio of phosphorus dissolution from the P-enriched slag did not change. With increasing the slag/solution mass ratio, the concentration of each element in solution increased, while their dissolution ratios decreased. Furthermore, the phosphorus dissolution ratio was suppressed in the case of the P-enriched slag with low CaO and high P2O5 concentrations. Appropriate conditions for various factors affecting phosphorus dissolution behavior from P-enriched slag were discussed.

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Chemical and Mechanical Factors on Phosphorus Dissolution Behavior from P-concentrated Slag

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Refining of High-Carbon Steel and Reduction of CO2 Emissions by Using Lignite Upgraded Coal Briquettes

Hideichi Matsuoka, Yoshiyuki Matsui, Wataru Adachi, Yuri Shibuya, Koichiro Semura

DOI:

10.2355/isijinternational.ISIJINT-2024-206

Abstract

This study investigated the use of sustainable coal (lignite) that can simultaneously satisfy three requirements: [1] Environmental issues (CO2), particularly Carbon dioxide Capture and Utilization (CCU) that reduces CO2; [2] Resource issues, particularly Enhancement of dephosphorization function in the refining process; and [3] Enhancement of refining high-carbon steel. This study confirmed that use in the steel making process of lignite upgraded coal briquettes gives possibility to functionally differentiate the reaction site of decarbonization and dephosphorization and to reduce CO2 emissions.

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Refining of High-Carbon Steel and Reduction of CO2 Emissions by Using Lignite Upgraded Coal Briquettes

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Effect of inhomogeneous microstructure on strength and fracture resistance in sharp edge of Japanese swords

Kwangsik Kwak, Takateru Yamamuro, Yoji Mine, Shigekazu Morito, Kazuki Takashima

DOI:

10.2355/isijinternational.ISIJINT-2024-224

Abstract

Microtensile and microfracture tests were performed on the sharp-edge regions of Japanese swords fabricated in the Muromachi and Showa periods, which are called old sword (OS) and modern sword (MS), respectively, to correlate the mechanical properties with the inhomogeneous microstructures. The hardness of the sharp-edge regions was characterised by the distribution of fine pearlite mixed in martensite microstructures. The OS containing a large fraction of fine pearlite exhibited a low hardness compared to the MS. Microtensile tests using sharp-edge specimens revealed a positive correlation between their tensile strength and strain-to-failure, as opposed to the common tendency in conventional carbon steels made by modern iron-making technology. The fracture surfaces of the sharp-edge specimens consisted of intergranular fracture and dimples. The tensile strength and dimple fracture area fraction were higher in the OS than in the MS. These findings suggest that the fine pearlite microstructure contributes to increased strength in the sharp-edge region through inhibiting the linkage of intergranular cracking owing to local plastic deformation. Microfracture tests using the sharp-edge specimens revealed that the intrinsic fracture resistance of both OS and MS was determined by the intergranular fracture, whereas the fine pearlite microstructure increased the resistance to crack propagation. The micromechanical testing study indicates that in the sharp-edge regions, their strength and fracture toughness are simultaneously enhanced by the presence of fine pearlite although depending on its distribution.

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Effect of inhomogeneous microstructure on strength and fracture resistance in sharp edge of Japanese swords

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Temperature Dependence and Prediction of Density of Alkali Silicate Slag Melts

Kenshi Fujino, Hiromichi Takebe

DOI:

10.2355/isijinternational.ISIJINT-2024-227

Abstract

We measured the density of eight types of molten alkali silicate slag within the range of 1,673–1,823 K using the Archimedean double-bob method. The melt density of binary alkaline silicate glass linearly increased with a decrease in temperature. The temperature coefficient of the density ranged from -21.5 to -13.2 × 10-5 g‧cm-3‧K-1, and its order corresponded to the order of the ionic radii of the alkali oxide components. We applied Doolittle's free volume theory by combining the reported values of melt viscosity with the measured densities and volume expansion coefficients of melts and glass solids to propose an equation for predicting melt density from slag composition and temperature. Melt densities in the range of 1,273–1,823 K were predicted and compared with experimental values.

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Temperature Dependence and Prediction of Density of Alkali Silicate Slag Melts

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Surface tension measurement of SiO2-Na2O-NaF system by maximum bubble pressure method

Osamu Takeda, Naoki Yamashita, Yuting Chen, Ryuki Higure, Xin Lu, Hongmin Zhu

DOI:

10.2355/isijinternational.ISIJINT-2024-233

Abstract

The surface tension of the mold flux is important because it governs the interfacial phenomena between the mold and molten/solid steel. The maximum bubble pressure (MBP) method is often used to determine the surface tension of molten slags. However, for liquid samples with high viscosity, such as molten silicate, the MBP is overestimated. In this study, a simple relaxation function was applied to determine the MBP using the gas flow-rate as a parameter. Consequently, a static MBP was obtained, and the surface tension was reliably measured. The surface tension of the SiO2-Na2O-NaF melts were measured over a wide composition range using the developed method. When SiO2-40 mol% Na2O was added to NaF, the surface tension of the melts gradually increased with increase in SiO2-Na2O concentration. When the NaF in SiO2-40 mol% NaF was replaced by Na2O, the surface tension of the melts did not change significantly at the beginning of the addition. It was considered that F- ion was exposed in the surface of melts instead of O2- ion. This result is consistent with the discussion of the relative strength of the bonding force between the constituent particles. The increase in the surface tension upon further replacement of NaF with Na2O was gradual, indicating that F- was relatively exposed more than O2- on the surface of the investigated melts.

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Surface tension measurement of SiO2-Na2O-NaF system by maximum bubble pressure method

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Initial oxidation of Fe–Cr alloys at different temperatures and atmospheric conditions: A ReaxFF molecular dynamics approach

Qin Hu, Zi-yu Lyu, Li-dong Xing, Chao Gu, Yan-ping Bao

DOI:

10.2355/isijinternational.ISIJINT-2024-235

Abstract

Oxidation behavior during the continuous casting process significantly impacts steel quality. This study investigated the oxidation process of iron–chromium (Fe–Cr) alloys at different temperatures and atmospheric conditions using the molecular dynamics method. Results indicated that during oxidation, Fe and Cr atoms lost electrons while O atoms gained electrons. The ratio of consumed O positively correlated with temperature and O concentration. Oxidation severity was higher at increased O concentrations and 1373 K, with the most severe oxidation occurring at lower temperatures with higher O concentrations. The oxidation rate constant in wet O concentrations was lower compared with pure O, with a higher oxidation kinetic index, indicating that continuous casting billets in water-cooled conditions should have a limited duration. The initial oxidation kinetics of the Fe-Cr alloy surfaces are all manifested as the initial rapid oxidation, followed by the slow oxidation growth process Additionally, Mean-Squared Displacement (MSD) of Fe atoms is larger than that of Cr atoms and Cr oxidizes in the inner layer to form a dense oxide, it prevents Cr from continuing to oxidize and diffuse outward, thus generating Fe-rich products on the surface of Fe-Cr alloys.

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Initial oxidation of Fe–Cr alloys at different temperatures and atmospheric conditions: A ReaxFF molecular dynamics approach

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BO-Catboost Model-based Prediction of Blast Furnace Coal Injection Rate

Lili Meng, Jinlong Wen, Ran Liu, Hongyang Li, Zhi Zheng, Jinxiang Liu, Mingliang Zhi

DOI:

10.2355/isijinternational.ISIJINT-2024-150

Abstract

As a critical parameter in blast furnace production, the coal injection rate is not only related to the stability of furnace condition, but also a vital index for evaluating production economy. In most of the blast furnaces, this parameter is often determined by the operator's experience. This paper establishes a coal injection rate prediction model based on the Catboost (category gradient boosting algorithm), which can provide a better basis for operators to control the parameter. At first, the collected steel production data were processed, the last time operational parameters that had greater impact on the coal injection rate were selected out as the input of the model, and the current time coal injection rate was used as the single output of the model. Next, the Catboost model was quoted, and the Optuna optimization algorithm based on the Bayesian principle was used to optimize the Catboost model (BO-Catboost), enhancing the model's capabilities and avoiding over-fitting phenomenon. Then, the effects of the Catboost model under different optimization algorithms were compared, and the prediction results of the BO-Catboost model were compared with the predictions of the ordinary Catboost, BO-Random Forest and BO-XGboost (Extreme Gradient Boosting) model. The results show that the BO-Catboost model is better than other models. Finally, a blast furnace coal injection monitoring system based on Web technology was established, which can display the coal injection prediction information on the board, the test shows that it has a certain guidance for the control of the coal injection rate.

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BO-Catboost Model-based Prediction of Blast Furnace Coal Injection Rate

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Role of retained austenite and deformation-induced martensite in 0.15C-5Mn steel monitored by in-situ neutron diffraction measurement during tensile deformation

Takayuki Yamashita, Satoshi Morooka, Wu Gong, Takuro Kawasaki, Stefanus Harjo, Tomohiko Hojo, Yoshitaka Okitsu, Hidetoshi Fujii

DOI:

10.2355/isijinternational.ISIJINT-2024-196

Abstract

An Fe-0.15C-5Mn-0.5Si-0.05Nb medium-Mn steel annealed at 660 °C and 685 °C both exhibited inhomogeneous deformation with Lüders deformation and followed by an extremely high work hardening stage, but with different Lüders strain and work hardening behavior. In-situ neutron diffraction measurements during tensile tests were performed to investigate changes in the phase stresses, the stress contribution to the strength of the constituent phases, and the crystal orientation of austenite. The role of each constituent phase on the deformation behavior and the crystallographic orientation dependence of austenite stability were examined. Deformation-induced martensite showed excellent phase stress and contributed to the strength of approximately 1000 MPa at around tensile strength, which is close to macroscopic tensile strength. Although austenite contributed less to the strength, during Lüders deformation and work hardening stages, it continuously transformed to martensite as the deformation progressed, suggesting that it mainly contributed to the ductility of the steels through a transformation-induced plasticity effect. Austenite transformed to martensite during Lüders deformation almost regardless of its crystallographic orientations. However, there was a tendency for more 311 oriented austenite grains to remain parallel to the tensile direction.

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Role of retained austenite and deformation-induced martensite in 0.15C-5Mn steel monitored by in-situ neutron diffraction measurement during tensile deformation

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Apparent Viscosity Measurement of Gas–liquid Multiphase Fluids by the Falling Ball Method

Yusaku Mita, Takayuki Iwama, Huafang Yu, Shin-ichi Shimasaki, Noritaka Saito, Ryo Inoue, Shigeru Ueda

DOI:

10.2355/isijinternational.ISIJINT-2024-246

Abstract

The recovery rate of iron is reduced if iron particles suspended in the refining slag do not sediment. The sedimentation rate of particle iron in the foaming slag is slower than in the slag in the single-phase liquid. Iron particles are especially likely to remain in the foaming slag. To predict the sedimentation rate of iron particles in the slag, it is necessary to derive an accurate viscosity of the foaming slag. However, it is difficult to estimate an appropriate value because the state of gas-liquid multiphase fluid changes the condition with time. Its apparent viscosity varies depending on the measurement method because it is a non-Newtonian fluid. In this study, to understand the sedimentation behavior of iron particles in foaming slag, a gas-liquid multiphase fluid was generated by glycerin solution. Its apparent viscosity was estimated by the Stokes equation using the falling-ball method. The sedimentation rate of stainless steel, titanium, and glass balls with a diameter of 2 mm were measured in a glycerin aqueous solution gas-liquid fluid. The sedimentation rate was non-uniform because the gas-liquid fluid's state differed depending on the position. The apparent viscosity of the fluid increased with an increase in the gas phase ratio. The variation of apparent viscosity with the conditions of the falling-ball method was also discussed. Furthermore, a comparison was made between the present results and the apparent viscosity measured by the rotational technique.

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Apparent Viscosity Measurement of Gas–liquid Multiphase Fluids by the Falling Ball Method

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Modification of the activities of components in Ca2SiO4-Ca3P2O8 solid solution at 1573 K

Keijiro Saito, Masakatsu Hasegawa

DOI:

10.2355/isijinternational.ISIJINT-2024-243

Abstract

The activities of components in Ca2SiO4-Ca3P2O8 solid solutions have been reported by preceding studies as the basic thermodynamic data for phosphorus removal in the steelmaking process. Since the reported activities contained the uncertainties accumulated from thermodynamic data, this study aimed to reevaluate the experimental results in the preceding studies. Firstly, the equilibrium constant of the following reaction used to calculate the P2O5 activities was measured at 1573 K through a gas equilibrium method.

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Modification of the activities of components in Ca2SiO4-Ca3P2O8 solid solution at 1573 K

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Structure Design and Phase Stability Analysis of Ca2SiO4-Based Solid-Solution Crystal in Molten Slag

Masanori Suzuki

DOI:

10.2355/isijinternational.ISIJINT-2024-257

Abstract

It is known that dephosphorization of molten iron is promoted by Ca2SiO4 precipitates in molten slag because they form a solid solution with Ca3P2O8. Crystal structure of the Ca2SiO4 precipitate is important because it strongly affects phosphorus solubility. Although the α phase of the solid solution shows extremely high phosphorus solubility at high temperatures, its phase transition easily occurs to the α' phase that has low phosphorus solubility when iron oxide is incorporated in slag. Phase stability of Ca2SiO4 crystal strongly depends on the solubility of foreign components, which influence the ionic configuration. To explore the optimum composition for enhancing structural stability of the α phase, this study conducted a structure design of Ca2SiO4-based solid-solution crystal by first-principles calculation based on density functional theory. The effect of foreign component solubility on the α phase stability was evaluated by free energy change of solid-solution formation. It was found that Ca2+ substitution with Fe2+ in α-Ca2SiO4 crystal makes the structure unstable, whereas Ba2+ incorporation enhances stability. In the latter case, oxygen ion configuration becomes distorted and the structure is relaxed. High-temperature in-situ X-ray diffraction analysis was performed to observe precipitation of the Ca2SiO4-based solid solution in a molten slag and its phase transition with decreasing temperature. The α phase of the Ca2SiO4-based solid solution initially precipitated at 2073 K, while the α→α' phase transition and precipitation of the calcium ferrite phase occurred at temperatures lower than 1673 K. It was verified that the Ba-bearing Ca2SiO4 precipitates in slag contained significant phosphorus content.

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Structure Design and Phase Stability Analysis of Ca2SiO4-Based Solid-Solution Crystal in Molten Slag

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Ductility loss of a metastable austenitic stainless steel and its TIG weldment due to hydrogen embrittlement at low temperatures considering the effect of pre-strain at 4K

Rafael Magalhaes De Melo Freire, Shohei Uranaka, Eita Tochigi, Mitsuo Kimura, Tomoya Kawabata

DOI:

10.2355/isijinternational.ISIJINT-2024-182

Abstract

The amount of martensite in austenitic stainless steels produced during plastic deformation at low temperatures is related to the reduction in hydrogen embrittlement resistance. A pre-strain at 4 K was employed in this work to produce strain-induced martensite (SIM) in the microstructure of SUS316L and its weldment to verify the changes in hydrogen embrittlement susceptibility through slow strain tensile (SSRT) tests in a high-pressure hydrogen environment. As the base metal specimens, the weld metal specimens, manufactured by gas tungsten arc welding (GTAW or TIG) were pre-strained at different levels (5%, 10%, and 15%) for comparison with the non-pre-strained condition. Analysis of the most degraded samples tested from -150 °C to 0 °C is conducted through fracture surface observations, lateral crack length measurement, and crack densities. It was possible to indicate that the pre-strain effect induced earlier crack nucleation in comparison to the situation observed in the non-pre-strained material. Moreover, the pre-existing martensite produced by the pre-strain at 4 K is responsible for earlier crack nucleation, leading to a loss in the hydrogen embrittlement resistance for the SSRT pre-strained base metal specimens.

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Ductility loss of a metastable austenitic stainless steel and its TIG weldment due to hydrogen embrittlement at low temperatures considering the effect of pre-strain at 4K

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Ductile Fracture Prediction During Metal Forming Using an Ellipsoidal Void Model and Some Other Models

Kazutake Komori

DOI:

10.2355/isijinternational.ISIJINT-2024-250

Abstract

This paper reviews studies on the prediction of ductile fracture during metal forming using an ellipsoidal void model and some other models proposed by the author and some relevant studies. Section 2 discusses the research on the theory of voids for predicting ductile fracture during metal forming. Section 3 summarizes the simulation method for predicting ductile fracture during metal forming using the ellipsoidal void model, and Section 4 summarizes the simulation result on the ductile fracture prediction during metal forming using the ellipsoidal void model. Section 5 shows the applicability of the ellipsoidal void model and the simulation result on the ductile fracture prediction during metal forming using some other models.

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Ductile Fracture Prediction During Metal Forming Using an Ellipsoidal Void Model and Some Other Models

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Phonon mean free path of silicate glasses: a useful parameter to distinguish between framework and nonframework cations

Sohei Sukenaga, Bunta Ozato, Yohei Onodera, Shinji Kohara, Masahiro Shimizu, Tsuyoshi Nishi, Rie Endo, Takaaki Tomai, Akira Yoko, Sakiko Kawanishi, Hiroshi Fukaya, Hiromichi Ohta, Hiroyuki Shibata

DOI:

10.2355/isijinternational.ISIJINT-2024-141

Abstract

Assuming that heat is transported by lattice vibrations (phonons) in silicate glasses, their thermal conductivity is correlated with the product of sound velocity, volumetric heat capacity, and phonon mean free path (MFP). The sound velocity and heat capacity have been studied extensively, but the origin of the composition-induced variation in the MFP remains unclear. The present study investigated MFP in M2/nO–SiO2 (Mn+: Li+, Na+, Ca2+, Sr2+, or Pb2+) glasses with a variation of M2/nO content. The MFP of the silica glass decreased with the addition of M2/nO. The effect of the type of metallic cation on the MFP was minimal for the selected alkali and alkaline-earth silicate glasses. By contrast, the MFP of lead silicate glasses was higher than those of alkali or alkaline-earth silicate glasses when the metallic cation contents were comparable. Previous studies have demonstrated that alkali and alkaline-earth cations act as nonframework species that break the silicate network structure, whereas lead cations have inconclusive structural roles. Our data indicate that lead cations partly act as framework cations and that phonons tend to be scattered near nonframework cations in silicate glasses. Thus, the phonon MFP is a useful parameter for determining the structural role of metallic cations in silicate glass via phonon propagation.

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Phonon mean free path of silicate glasses: a useful parameter to distinguish between framework and nonframework cations

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Effect of intercritical annealing on microstructure and toughness of medium-Mn steel with elongated prior-austenite grains formed via two-step hot rolling process

Kyosuke Matsuda, Takuro Masumura, Toshihiro Tsuchiyama, Misa Takanashi, Takuya Maeda, Shuichi Nakamura, Ryuji Uemori

DOI:

10.2355/isijinternational.ISIJINT-2024-180

Abstract

Fe-9 mass%Ni alloy is widely used as a cryogenic steel owing to its excellent low-temperature strength and toughness. However, Ni is an expensive element, with medium-Mn steel considered an inexpensive alternative. Considering the Fe-10%Mn-0.1%C alloy is brittle at low temperatures, the application of intercritical annealing with two-step hot rolling could lead to toughening. Herein, the effect of intercritical annealing on the toughness of a Fe-10%Mn-0.1%C alloy with elongated prior-austenite grains (PAGs) formed via a two-step hot-rolling process was investigated. Intercritical annealing was performed on the specimens with and without two-step hot rolling. For both specimens, intercritical annealing resulted in softening of α'-martensite and an increase in the amount of retained austenite. In the specimen not subjected to the two-step hot rolling process, the fracture morphology transitioned from ductile to intergranular with a decrease in the temperature. Intercritical annealing improved the toughness when ductile fracture occurred. In the case of intergranular fracture, the effect of intercritical annealing on the toughness was negligible. In the two-step hot-rolled specimen with elongated PAGs, the fracture morphology transitioned from ductile to separation fracture with ductile fracture, and intercritical annealing improved the toughness at all temperature ranges. The improvement in toughness during separation fracture is attributed to the expansion of the plastic zone owing to ductile crack progression and the formation of sub-cracks, which promote the strain-induced transformation of retained austenite and ε-martensite.

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Effect of intercritical annealing on microstructure and toughness of medium-Mn steel with elongated prior-austenite grains formed via two-step hot rolling process

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Enhanced Resistance to Delayed Fracture in 0.09 mass% P-Doped High-Strength Steel Processed by Warm Tempforming

Yuuji Kimura, Taku Moronaga, Kaneaki Tsuzaki

DOI:

10.2355/isijinternational.ISIJINT-2024-189

Abstract

From the viewpoint of expanding the allowable P limit, the effect of warm tempforming on delayed fracture resistance was evaluated for 0.09% P-doped 0.4%C–1%Cr–0.7%Mn–0.2%Mo steel (mass%). The P-doped steel was warm tempformed at 500 °C with a caliber-rolling reduction of 78% and annealed at 550 °C for 1 h. This thermomechanical treatment created an ultrafine elongated grain structure with a strong <110>// rolling direction fiber texture, in which P definitely cosegregated with Mn and Mo at grain boundaries. The slow-strain-rate-test and immersion test demonstrated that warm tempforming markedly enhanced the delayed fracture resistance of the P-doped steel at a tensile strength of 1100 MPa level, in contrast to conventional quenching and tempering treatment.

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Enhanced Resistance to Delayed Fracture in 0.09 mass% P-Doped High-Strength Steel Processed by Warm Tempforming

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Comparison of the viscoelastic properties and viscosity of suspensions determined by oscillation and creep testing

Kento Nakanishi, Takehiro Sumita, Noritaka Saito, Kunihiko Nakashima

DOI:

10.2355/isijinternational.ISIJINT-2024-078

Abstract

Knowledge of the viscoelastic properties of suspensions is essential for many industrial processes. Although oscillation and creep testing are widely used to measure the viscoelastic properties of complex fluids, few studies on the correlation between the viscoelastic properties measured using these methods have been published. This study aims to provide insights into the differences between these methods and determine which method is better suited for a particular application. The room-temperature viscoelastic properties of a suspension composed of polyethylene beads dispersed in a silicone oil matrix were measured by oscillation and creep testing and compared. The results of oscillation testing indicated that the suspension showed weakly elastic deformation, whereas the results of creep testing revealed that the suspension was relatively elastic, with the liquid phase showing lower viscosity. In addition, the viscosity measured by oscillation testing was lower than that measured by creep testing. When the imposed flow causes microstructural changes, such as when the shear flow and particle‒particle contact induce aggregation, the analyzed flow property considerably differs between testing methods.

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Comparison of the viscoelastic properties and viscosity of suspensions determined by oscillation and creep testing

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Effect of Fluoride Ions in Slag on the Dynamic Change of the Interfacial Tension between Liquid Iron and Molten Slag

Masanori Suzuki, Kenta Iwakura, Yuichi Tsukaguchi, Kazuaki Mishima

DOI:

10.2355/isijinternational.ISIJINT-2024-134

Abstract

The interfacial tension between the liquid steel and molten slag is one of the key properties to control the entrapment of mold flux in molten steel in the continuous casting process. A dynamic change of the interfacial tension is observed when deoxidized iron and silicate slag are in contact, which can be explained by the oxygen absorption and desorption at the iron/slag interface. However, the dynamic change of the interfacial tension is influenced by other surfactant components of the molten iron and slag. Fluoride ions are fundamental component of mold flux, and recognized as the surface active component of molten slag. The effect of fluoride ions in slag on the interfacial tension has not been critically evaluated. Here, the effect of fluoride ions in slag on the interfacial tension between molten iron and molten silicate slag was evaluated at 1823 K, where the fluoride-containing slag compositions were designed to exhibit the same SiO2 activity and slag viscosity as those of the fluoride-free slag. Compared with the case of molten iron and fluoride-free slag, the interfacial tension between the molten iron and fluoride-containing slag was initially lower. Except the effect of oxygen adsorption, fluoride ion was considered to directly decrease the interfacial tension. However, as the fluoride content in slag was higher, the interfacial tension tended to show the higher value at the final state. This behavior was attributed mainly to fluoride vaporization as SiF4, which reduce the SiO2 activity in slag and thus equivalent oxygen content at the iron/slag interface.

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Effect of Fluoride Ions in Slag on the Dynamic Change of the Interfacial Tension between Liquid Iron and Molten Slag

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Constitutive Description of Flow Curve for Duplex Titanium Alloy for Hot Forming under Elevated Temperature

Yuki Shimomura, Hyung-Won Park, Hyeon-Woo Park, Yuji Sato, Jun Yanagimoto

DOI:

10.2355/isijinternational.ISIJINT-2024-014

Abstract

A novel integrated constitutive equation of the flow curve for Ti–6Al–4V alloys is proposed by incorporating the effects of phase fraction in the hot-forging temperature range. The flow curve was obtained using hot-compression tests in the temperature range of 750–1050 °C and strain rate range of 1–25 s-1. The effects of friction and deformation heat generated during compression were corrected using the inverse analysis method to identify the ideal uniaxial flow curve. The obtained stress parameters were satisfactorily regressed using the rule of mixtures on the α and β phases considering changes in the phase fraction. The integrated flow curve equation incorporating the rule of mixtures of the two phases effectively expressed the flow curve throughout the investigated temperature range. The internal microstructural observation showed that the continuous dynamic recrystallization of the α phase is dominant in the α+β two-phase region, while the deformation of the β phase becomes dominant just below the β transus. The constitutive equation presented here is in good agreement with the temperature dependence of the microstructure.

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Constitutive Description of Flow Curve for Duplex Titanium Alloy for Hot Forming under Elevated Temperature

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