Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
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Displaying 1-18 of 18 articles from this issue
  • Takeru Hashiguchi, Kenji Matsuda
    Article type: Regular Article
    Article ID: TETSU-2024-004
    Published: 2024
    Advance online publication: March 19, 2024
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    For manufacturers, rapid and accurate quality control of materials and products in the field is essential for improving competitiveness. Rebound hardness testing is one of the fundamental material tests expected to meet this requirement. However, it has been known that many factors affect rebound hardness which may cause the fluctuation in the measured value. In order to elucidate the effect of the fixing method of the specimen, the coefficient of restitution of a hammer using a Vickers indenter was compared with and without bolting the specimen to the base. The motions of the hammer and the specimen were measured simultaneously using two laser Doppler vibrometers and were also numerically analyzed using an elastoplastic finite element method. It has been clarified that, in the case of without bolting, the restitution coefficient is decreased compared to with bolting. The decreasing tendency becomes larger as the impact point moves away from the specimen center. The rebounding behaviors of the hammer and the specimen without bolting can be reproduced with a numerical model in which an appropriate elastic film is inserted between the specimen and the base. The numerical results show that the hammer impact causes rigid body motion in the specimen, which consumes hammer energy, resulting in a decrease in the coefficient of restitution. The range in which the coefficient of restitution can change is also evaluated by assuming a simple two-body collision model.

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  • Takahiro Kamimoto, Yoshihiro Deguchi
    Article type: Regular Article
    Article ID: TETSU-2023-087
    Published: 2024
    Advance online publication: March 12, 2024
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    In the measurement of iron and steel processes, the measurement of temperature concentration distribution is very important for the analysis and control of in-furnace phenomena in order to obtain in-furnace information. However, thermocouples and gas sampling methods are used, but since they are contact and point measurements, they disturb the measurement field, require modification of equipment and piping, have low time response (10 Hz), and are affected in accuracy (20% or more) by environmental fluctuations. This report describes the development of a technology for simultaneous measurement of multiple components such as O2, CO, and CO2 concentrations in a furnace, acquisition of a spectral database necessary for measurement using various calibrators, adjustment of the optical axis when installing a sensor with a large laser beam path length (several tens of meters), and development of a technology for adjusting the optical axis by feeding back the laser beam position in real time to prevent optical axis fluctuations during equipment operation. We have developed a technology to adjust the optical axis by feeding back the position of the laser beam in real time when the optical axis fluctuates during the operation of the equipment.

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  • Chihiro Hayama, Mariko Kadowaki, Yoshiharu Murase, Hideki Katayama, To ...
    Article type: Regular Article
    Article ID: TETSU-2024-005
    Published: 2024
    Advance online publication: March 12, 2024
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    This paper presents the effect of P addition on the corrosion resistance of steels before and after rust formation. Electrochemical measurements and surface analysis of P-containing steels (Fe-0.5 mass% P, Fe-1.0 mass% P, and Fe-1.5 mass% P) were conducted to analyze the contribution of P to their initial corrosion resistance before rust formation. The results showed that the initial corrosion resistance of the steel was worse with higher P content. According to the surface analysis conducted by SEM/EDS, more P-segregations at grain boundaries existed with higher P content. Based on the results of polarization measurements, it was considered that these P-segregation became the initiation sites of localized corrosion, resulting in the decrease in the initial corrosion resistance.

    Although the initial corrosion resistance was worse with higher P content, the long-term corrosion resistance was better with higher P content. According to the results of atmospheric exposure tests at Miyakojima and the surface analysis of rust layers, P was incorporated into the rust layer, and it promoted the protective ability against corrosion.

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  • Kenta Matsumoto, Takeru Sunada, Yuki Murata, Tomohiro Yoshida, Yuki Mo ...
    Article type: Regular Article
    Article ID: TETSU-2023-109
    Published: 2024
    Advance online publication: March 08, 2024
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    Ionic liquids are salts, and their melting points were less than 100 ºC under atmospheric pressure. In particular, ionic liquids, which melting point of them were less than room temperature under atmospheric pressure, have been researched in recent decades. Ionic liquids are well-known to designer’s solvents since configuration of cation and anion are easily to change then specificity is exhibited. In this work, novel protic ionic liquids (PILs) which are applied for CO2 sorption materials have been synthesized using aromatic amine such as alkylpyridine derivatives and N,N-dimethylaniline and bis(trifluoromethanesulfonyl)amide due to co-existing proton conductivity and hydrophobicity. Synthesized PILs exhibited hydrophobicity since 1-octanol–water partition coefficients were more than 0. Also, their ionic conductivities were approximately 10-3 S cm-1 at room temperature, and their mechanism of ionic conduction were different one compared with general electrolyte solution due to high viscosities. In addition, several PILs were high selectivity for CO2 sorption compared with N2. Furthermore, PILs gelatinized with bis[4-(1H,1H,2H,2H-tridecafluorooctyl)phenyl] terephthalates due to improvement of mobility. Some of gel–sol transition temperatures of 5wt% gels were approximately 100 ºC. The driving force of gelation with ionic liquids might be an entropy driven. Sorption selectivity for CO2 and N2 were similar one before and after gelation.

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  • Yoshiyuki Egashira, Noritaka Saito, Kunihiko Nakashima
    Article type: Regular Article
    Article ID: TETSU-2024-008
    Published: 2024
    Advance online publication: March 02, 2024
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    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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  • Shin-ichi Shimasaki, Shigeru Ueda, Noritaka Saito
    Article type: Regular Article
    Article ID: TETSU-2023-111
    Published: 2024
    Advance online publication: February 27, 2024
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    In the steel making process, most slags and fluxes often contain solids phase such as CaO. It is well known that the suspension in which solid phase are suspended has higher viscosity than that of pure matrix liquid. Therefore, it is expected that the viscosity of slag containing solid phase will increase. In this study, terminal settling velocity of particle in suspension has been measured. The suspensions consist of 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 bearing ball becomes slower than that in pure silicone oil. It was clarified that the retardation of the terminal velocity and the increasing of drag coefficient depend only on the volume fraction of solid phase (the polyethylene beads) of the suspension, and it is 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 suspension was proposed.

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  • Koga Hori, Kengo Kato, Hideki Ono
    Article type: Regular Article
    Article ID: TETSU-2024-003
    Published: 2024
    Advance online publication: February 23, 2024
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Increasing the utilization of steel scrap is strongly required for reducing CO2 emission in iron- and steel-making processes. In steel scrap recycling, the content of tramp elements in steel (such as copper and tin) inevitably increases. Accordingly, it is important to understand the thermodynamic characteristics of relevance to the accumulation of tramp elements in molten steel. The values of the interaction coefficients of Mo, B, Ni, Ti, and Nb with Sn in molten iron were reported previously. However, little is known about the interaction coefficients of alloying elements with tramp elements in molten high-chromium steel. In this work, the interaction coefficients of Mo, B, Ni, Ti, and Nb with Sn in the molten Fe–18mass%Cr alloy were measured at 1873 K by a chemical equilibration technique that uses the liquid immiscibility of the Fe–18mass%Cr alloy and Ag, yielding the following results:

    The results show that the values of the interaction coefficients of M with Sn in the Fe-18mass%Cr alloy are smaller than those for molten iron, which were measured in the previous work, except for titanium. The interaction coefficients of M with Sn in Fe and Fe–18mass%Cr alloy were estimated based on a regular solution model. The estimated interaction coefficients of B, Ni, and Ti with Sn in molten iron and Ni and Ti with Sn in the molten Fe–18mass%Cr alloy reasonably agree with the measured values.

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  • Takumi Aibara, Yoshiaki Morisada, Kohsaku Ushioda, Masayoshi Kamai, Ta ...
    Article type: Regular Article
    Article ID: TETSU-2023-113
    Published: 2024
    Advance online publication: February 22, 2024
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    The microstructural evolution and tensile properties of joints fabricated by the newly developed cold spot joining (CSJ) method were investigated using galvannealed DP 780 MPa steel sheet. The novel solid-state joining method called CSJ is proved to make the joining interface plastically deformed under high pressure and appropriate current by expelling Zn-Fe coated layer, resulting in the sound joints with strong interface. Joints exploiting CSJ method were made focusing on the effects of the pressing speed and current level. Microstructural observations of the joints revealed that the lower pressing speed increases the interface temperature. In addition, the increase in the current also increases the interface temperature. The increase in the interface temperature has a positive effect in terms of expelling Zn-Fe coated layer. The positive effect of increasing current is more significant than that of decreasing the pressing speed. The increase in temperature near the interface by increasing current promotes the removal of the Zn-Fe coating layer, resulting in plastic deformation near the joining interface. Appropriate pressure and current settings can facilitate the sound spot joints with enough tensile strength. Both tensile-shear and cross-tension tests have confirmed a plug failure in the base material region.

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  • Ryoto Okumura, Yuto Adachi, Yasumitsu Kondo
    Article type: Regular Article
    Article ID: TETSU-2023-115
    Published: 2024
    Advance online publication: February 22, 2024
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    Blistering occurs when oxide scale swells during oxidation at steel high temperatures.Blistered scale causes surface defects when steels are rolled. An assumption has been proposed that the pressure of CO and CO2 gas generation beneath the scale causes blisters. This study the qualitative measurements of the gas pressure beneath the oxide scale were tried.A stainless tube was set in order to connect to the beneath the scale during oxidation.Positive pressures were confirmed beneath oxide scale. Also gas permeability through FeO mono-layer scale was obtained.

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  • Masaki Chiba, Kensuke Misawa, Hisanori Tanimoto, Masayoshi Kumagai, Sh ...
    Article type: Regular Article
    Article ID: TETSU-2023-112
    Published: 2024
    Advance online publication: February 09, 2024
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    To understand the mechanism of vibration energy harvesting using magnetostrictive Fe-Ga alloys, the dynamic strains at different locations of a U-shaped device during vibration were simulated. In the simulations, the previous results for location-dependent strain in the vibration experiments were fitted with trigonometric functions. The results show that the amplitude and phase of the strain vary with location, and that the electromagnetic force is generated at different locations. Since magnetic induction is thought to occur due to an external magnetic field, the magnetic domain structure near the cube orientation of Fe-Ga alloy single crystals was observed using a Kerr effect microscope. As a result, Bloch magnetic domain structures with different contrasts of brightness and darkness were observed depending on the applied magnetic field. It was shown that striped magnetic domains were dominant when the applied magnetic field was small, while lancet magnetic domains oriented to the magnetic field appeared with transverse straight supplementary domains as a magnetic domain under a saturated magnetic field. The domain patterns in one direction magnetic fields were not necessarily the same as those observed in the opposite direction. This indicates that Fe-Ga alloy single crystals are used as a core for vibrational energy harvesting. Also, the motion of magnetic walls is thought to play an important role in the vibrational properties of the material, and inhomogeneous elastic strain associated with magnetic domains evolves microscopically in single crystals.

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  • Rihoko Miyazaki, Kosei Oikawa, Shinsuke Kunimura
    Article type: Regular Article
    Article ID: TETSU-2023-114
    Published: 2024
    Advance online publication: February 06, 2024
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    In this study, total reflection X-ray fluorescence (TXRF) spectra of dry residues of 10 μL, 100 µL, 200 µL, and 400 μL droplets of a solution containing 10 μg L−1 of Cr on hydrophobic film coated sample holders were measured by a portable TXRF spectrometer, and these spectra were compared. The net intensity of the Cr Kα peak per the concentration of Cr in the sample solution (counts / μg L−1) increased with an increase in the volume of a droplet of the sample solution. This was because the mass of Cr in the dry residue increased with an increase in the volume of a droplet of the sample solution. This enhancement in the net intensity of the Cr Kα peak per the concentration of Cr led to a significant improvement in the detection limit expressed as the concentration of Cr. Detection limits for Cr obtained from the measurements of the dry residues of 10 μL, 100 µL, 200 µL, and 400 μL droplets of the sample solution were 2.1 μg L−1, 0.30 μg L−1, 0.13 μg L−1, and 0.09 μg L−1, respectively. Measuring the dry residue of a large volume droplet of a water sample would be useful for the analysis of trace elements in the sample.

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  • Daisuke Igawa, Yusuke Dohi, Takashi Matsui, Tetsuya Yamamoto, Kiyoshi ...
    Article type: Regular Article
    Article ID: TETSU-2024-001
    Published: 2024
    Advance online publication: January 23, 2024
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    In our previous paper, a new measurement method for the coal adhesion property called “surface tension of semi-coke” was devised. The surface tension of a semi-coke sample obtained by heat treatment of a coal sample at 500°C was measured as a unique adhesion property. Conventionally, it has been thought that adhesion is dominant under a low MF (Gieseler maximum fluidity) condition. Moreover, it is important for effective coal utilization to develop a technique that enables production of high strength coke under low MF conditions, which has been thought to deteriorate coke strength. However, in the previous paper, the effect of surface tension on coke strength was investigated only under a single MF condition without changing the level of MF.

    In this paper, the effects of surface tension on coke strength under adhesion dominant conditions (low MF and high TI (total inert content)) were investigated. As a result, it was found that the effect of surface tension on coke strength was significant when MF was low or TI was high. Therefore, it is considered that high strength coke can be produced even under low-grade conditions (low MF or high TI) by controlling surface tension. Finally, based on the results, the concept of the conventional MOF diagram was extended. This technique enables effective selection and utilization of coal resources.

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  • Shin-ichi Shimasaki, Shigeru Ueda, Noritaka Saito, Kenji Katoh
    Article type: Regular Article
    Article ID: TETSU-2023-101
    Published: 2024
    Advance online publication: January 11, 2024
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    In the steelmaking process, molten slag is foamed through gas injection and gas generation reactions, and molten iron droplets get mixed and trapped in the slag. A settling velocity of an iron droplet in the foaming slag are very important, because a residence time of an iron droplet in the slag is directly calculated the settling velocity. According to the previous research, the settling velocity is expected to be slower than in regular non-foaming slag. However, it has yet to be quantitatively clarified. This study measured the settling velocities of particles through a foaming liquid of glycerin-water solution. A dimensionless correlation equation for particle settling velocity in the formed liquid was proposed by conducting a dimensional analysis of the experimental data. Using the obtained equation, we have predicted the settling velocity of iron particles in the foaming slag. It was clarified that the settling velocity of iron particles is highly affected by a volume fraction of gas phase in the foaming slag. There is a certain threshold for the velocity, and the velocity abruptly became zero when it falls below that threshold.

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  • Susumu Imashuku
    Article type: Regular Article
    Article ID: TETSU-2023-100
    Published: 2023
    Advance online publication: December 14, 2023
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    Identifying a crystal structure of alumina (Al2O3) scale is critical for evaluating the performance of heat-resistant alloys because α-Al2O3 is stable and protective against high-temperature oxidation and corrosion but θ- and g-Al2O3 provide poor oxidation resistance. Conventional methods to identify crystal structures of Al2O3 scales are time-consuming. Herein, the author proposes a method to rapidly identify crystal structures of Al2O3 scales on β-NiAl by obtaining their cathodoluminescence (CL) spectra. α-, θ-, and g-Al2O3 can be identified by detecting a sharp peak at 695.8 nm and 686.3 nm, and a broad peak at around 700 nm, respectively, in CL spectra. Concentrations of α-, θ-, and g-Al2O3 scales can be determined roughly from intensities of these peaks. This method can be applied to areas ranging from the millimeter to micrometer scale, and the acquisition time for the CL spectra was less than 10 s. The results indicate that obtaining CL spectra contributes to the identification of crystal structures of Al2O3 scales on heat-resistant alloys and a reduction in time to evaluate the performance of heat-resistant alloys.

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  • Yoshihiko Higuchi, Shin-ichi Shimasaki, Shigeru Ueda, Noritaka Saito
    Article type: Review
    Article ID: TETSU-2023-103
    Published: 2023
    Advance online publication: December 12, 2023
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    In the process of steelmaking refining, slag used in the preliminary treatment of molten iron or the converter is a multiphase melt. It contains solid particles that cannot dissolve entirely from the raw materials and gas bubbles generated through reactions, thus making it a multiphase molten material with dispersed components. The flow characteristics of the suspensions, foams, and emulsions significantly affect the separation of iron particles in the slag and the behavior of slag discharge. Multiphase melts typically behave as non-Newtonian fluids, so the evaluation, focusing on viscosity, is crucial to understanding their flow characteristics. This report reviews recent advances in slag visualization techniques for understanding the flow of multiphase molten materials. The results are as follows:

    Through studies of viscosity measurements of multiphase melts using rotational viscometers, falling-ball methods, and dam break methods in cold experiments with simulated slag and high-temperature experiments with slag compositions close to practical operation, it has been shown that the apparent viscosity increases with an increase in the volume fraction of solid particles and bubbles. The complex behaviors of the viscosity measurement values could have been reproduced with high precision using predictive models based on recent developments in machine learning. In terms of process evaluation, the application of mesh and mesh-free methods is advancing as methods of computational fluid dynamics (CFD) that take non-Newtonian behavior into account, providing valuable insights into evaluating slag discharge properties and more.

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  • Kenji Katoh, Tatsuro Wakimoto
    Article type: Regular Article
    Article ID: TETSU-2023-098
    Published: 2023
    Advance online publication: November 18, 2023
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    We experimentally investigated the rupture conditions of a thin film of an aqueous surfactant solution when a spherical particle with a finite falling velocity penetrates the film. When the sphere passes through the film, the film wraps around the sphere, and a gas layer is maintained between the film and the spherical surface. When the velocity of the sphere is small, perforation occurs in the wrapping film below the equator of the sphere and the contact line moves along on the sphere surface. The energy instability occurs at a certain position of the contact line on the sphere surface, leading to rupture of the entire thin film. As the sphere velocity is increased, the perforation of the wrapping film occurs above the equator. In this condition, the probability of thin film rupture increases, since the perforation of the wrapping film immediately leads to rupture of the entire film. The motion of the gas between the thin film and the spherical surface was considered analytically from the balance between surface tension and viscous force. According to the result, the velocity condition above which the wrapping thin film could exist beyond the equator of the sphere was evaluated.

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  • Ko-ichiro Ohno, Taiga Eguchi, Tatsuya Kon
    Article type: Regular Article
    Article ID: TETSU-2023-093
    Published: 2023
    Advance online publication: November 07, 2023
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    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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  • Satoshi Hasui, Yoshihiko Higuchi
    Article type: Regular Article
    Article ID: TETSU-2023-075
    Published: 2023
    Advance online publication: October 19, 2023
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    To meet the increasing demand for low-impurity steel products, powder top blowing has been applied to the steelmaking process. Powder reagents penetrating deeper into the molten metal lead to longer resident time and higher efficiency of refining. Many studies have been performed on the basis of cold model experiments with a single liquid phase for clarifying the penetration behavior of the particle. However, the effects of the second liquid phase have been reported little whereas molten slag often exists on the surface of molten metal in the steelmaking process.

    In the present work, the sphere was penetrated into the fluids consisting of a silicone oil layer and water bath. The time variation of the penetration depth of the sphere was measured with a high-speed camera. Effects of the type and size of the sphere, entry velocity, and oil depth were estimated. As a result, the stagnation of penetration occurred under the condition of no air column behind the sphere. On the other hand, a thin oil layer led to no stagnation and deeper penetration due to promoting the formation of air or oil columns. However, an oil layer thicker than 2 mm suppressed the penetration by decreasing the kinetic energy under the condition of high viscosity. The same penetration behavior was observed with a smaller sphere. However, the behavior was more sensitive to the effect of buoyant force because the size of the residual bubble on the surface of the sphere became relatively bigger than the sphere.

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