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

ISIJ International Vol. 62 (2022), No. 1

  • Improvement of Carbothermic Reduction of Copper Smelting Slag and Valuable Constituents Recovery

    pp. 1-11

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    DOI:10.2355/isijinternational.ISIJINT-2021-136

    In order to comprehensively utilize copper smelting slag, the effect of strengthening measures on the reduction rate of the copper smelting slag, reduction kinetics, magnetic separation of reduced pellet and volatilization of residual valuable constituents were investigated in the present study. Milling for mechanical activation was the most efficient method to improve the reduction rate of copper smelting slag compared to addition of Na2CO3 catalyst and high reactivity reducing agent. The metallization degree of reduced pellet increased from 54.5% to 75.5% when the slag-coal mixture was milled for 30 s and reduced at 1100°C for 30 min. The apparent activation energy for the reduction of milled pellet increased from 96.1 kJ/mol to 153.5 kJ/mol. The iron concentrate magnetically separated from the milled pellet reduced at 1200°C had the best quality. The removal rates of typical elements during direct reduction-magnetic separation decreased in the sequence of Zn>K>Na>Cu. Secondary-dust captured from the flue gas contained 70.17 mass% Zn and 11.99 mass% Pb, which could meet the requirements of I grade zinc ore. The Zn in the dust existed in the form of ZnO. The productivity of the dust was around 1.49%. The application of mechanical milling in the reduction of copper smelting slag/coal composite pellet can improve the reduction efficiency of iron oxide and the quality of Zn-rich secondary dust. This work can help to enhance the utilization of copper smelting slag in a more efficient and sustainable method.
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  • Aluminum Deoxidation Equilibrium in Molten Fe–Co Alloys

    pp. 12-19

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    DOI:10.2355/isijinternational.ISIJINT-2021-267

    Aluminum deoxidation equilibrium of molten Fe–Co alloy was experimentally measured using a chemical equilibrium method and numerically assessed using a sub-regular solution model based on Darken’s quadratic formalism and a Redlich-Kister type polynomial at 1873 K. It was found that the degree of oxygen content reduction by Al-deoxidation decreased with increasing cobalt concentration in the alloy, peaking at around 40 to 60 mass% Co, and then improved with further increase in cobalt concentration. The following binary interaction parameters between cobalt and aluminum were derived in this study:0ΩCo-Al = -387360 [J/mol], 1ΩCo-Al = 309420 [J/mol]It was also found that the above binary interaction parameters can accurately determine Al-deoxidation equilibrium of pure liquid cobalt. Finally, the critical point at which Al2O3 and CoO·Al2O3 coexist throughout the whole composition range of the alloy was also estimated from the experimental results in this study.
  • Evolution of Mercury from Iron Ores in Temperature-Programmed Heat Treatments

    pp. 20-28

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    DOI:10.2355/isijinternational.ISIJINT-2021-295

    The behavior of Hg released from iron ores during temperature-programmed heat treatments (TPHTs) in air has been mainly studied using an online monitoring method. The Hg release behavior in TPHT significantly depends on the type of ore being processed, which includes forms evolved as Hg0 and Hg2+, and forms that remain thermally stable up to 950°C. In addition, the TPHT experiments for model Hg compounds suggested the presence of several types of Hg forms (HgCl2, Hg2Cl2, HgS, HgO, HgSO4, and associated mineral-Hg) in the iron ores used. The amounts and proportions of suggested forms of Hg species substantially depend on the type and composition of the iron ore used. These observations may be important in designing an efficient method for the removal of Hg from iron ore and gaseous Hg.
  • Distinct Difference in High-temperature Characteristics between Limonitic Nickel Laterite and Ordinary Limonite

    pp. 29-37

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    DOI:10.2355/isijinternational.ISIJINT-2021-307

    In order to achieve the effective utilization of limonitic nickel laterite for stainless steel production at lower cost, the distinct difference in high-temperature characteristics between limonitic nickel laterite and ordinary limonite has been systematically expounded via compact sintering method and the comparative analysis of the relevant sintering performance at the suitable basicity has also been conducted through sinter pot tests. The results indicate that limonitic nickel laterite possesses much poorer assimilability and liquid phase fluidity due to the abundant high-smelting minerals compared with ordinary limonite. The strength of bonding matrix of limonitic nickel laterite is relatively better as the basicity is not exceed 1.4 while that of ordinary limonite is maintained at a higher level with the basicity of no less than 1.8. Meanwhile, the former is far weaker than the latter due to the much less amount of liquid phase, rather higher porosity and looser microstructure of the bonding matrix. Limonitic nickel laterite is identified as a far more refractory ore for sintering compared with ordinary limonite, further supported by sinter pot tests. It is essential to strengthen limonitic nickel laterite sintering from the standpoints of how to promote the liquid phase formation and densification of the sinter.
  • Coupled Simulation of Flow and Chemical Reaction with Finite Reaction Rate for Decarburization of Molten Iron using Gas Jet of Carbon Dioxide

    pp. 38-47

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    DOI:10.2355/isijinternational.ISIJINT-2021-296

    We proposed a novel numerical method for the reliable prediction of decarburization with CO2. In our method, mass, momentum, and energy conservation equations are solved simultaneously, where the reactive mass transfer, compressibility, and moving interface between gas and liquid are fully considered. In the decarburization reaction model, we assumed that the rate-limiting processes are the mass transfer in the gas phase and the interfacial reaction rate. Our method quantitatively well reproduced the total decarburization rates in the crucible of Nomura and Mori’s experiment (Trans. ISIJ, 13 (1973), 265.) using a jet of CO2–CO gas mixture. It was found that the interfacial reaction rate affected the local decarburization reaction rate and the concentration distribution of CO2 and CO near the gas–liquid interface. Thus, the consideration of the interfacial reaction rate is important for the accurate reproduction of the local decarburization phenomena by a gas jet of CO2.
  • Chlorination of ZnFe2O4 in Molten MgCl2–KCl

    pp. 48-55

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    DOI:10.2355/isijinternational.ISIJINT-2021-348

    Recovery of zinc from electric arc furnace dust (EAF dust) has been an important issue for the steelmaking industry, yet a sustainable technology is absent. As a fundamental study to develop a new process of recovering metals from EAF dust by using molten salt, this work clarifies the reaction behavior of solid ZnFe2O4 in molten MgCl2–KCl at temperatures from 773 K to 973 K. MgCl2 is the chlorinating agent and KCl is an additive to make a low melting point molten salt. The experimental results indicate the efficacy of converting ZnFe2O4 to ZnCl2 and FeClx (x = 2 or 3) by MgCl2. Zn is chlorinated prior to Fe in ZnFe2O4 under all conditions, implying the possibility of separating Zn from Fe. Improving the mass transfer in the melt accelerates the reaction. Lower temperatures and larger O2 partial pressure favor the selective chlorination of Zn, yet the reaction is more stagnant. This work has thus demonstrated the feasibility of treating EAF dust by using MgCl2-based molten salt.
  • Effect of an AC Magnetic-field on the Dead-zone Range of Inclusions in the Circular Channel of an Induction-heating Tundish

    pp. 56-63

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    DOI:10.2355/isijinternational.ISIJINT-2021-352

    In this paper, the radial electromagnetic force in the horizontal circular channel of an induction-heating tundish is derived. A dimensionless trajectory model of the inclusion is developed and numerically solved to acquire the trajectory of the moving inclusion. When the inclusion is in the lower half of the horizontal circular channel, the direction of the vertical component of the radial electromagnetic pinch force which acts on the inclusion is opposite to the buoyancy. Provided their magnitudes are the same, there is a balanced-position for the inclusions in a circular channel. Therefore, a dead-zone exists near the balanced-position, where the removal time of the inclusion with an AC magnetic-field is longer than without it. Then, the effect of the AC magnetic-field parameters on the range of the dead-zone is identified, which makes it possible to improve the removal efficiency of inclusions. The range of the dead-zone decreases with increasing magnetic-field intensity. When the dimensionless magnetic-field intensity is 56.3, the shielding parameter of 10–15.9 are optimal to decrease the range of the dead-zone.
  • Behavior of Carbon Adhesion on Aged Coking-chamber Walls to Pushing Load

    pp. 64-73

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    DOI:10.2355/isijinternational.ISIJINT-2021-057

    A common problem observed in aged coke plants is the increase in pushing load during the discharge of coke mass, arising from irregularities on the damaged coking-chamber walls. Usually, the chamber wall is partially covered with adhered carbon. Because carbon growth is influenced by a number of factors, the chamber wall has a complicated carbon adhesion distribution, and the amount of carbon-covered area differs from chamber to chamber. Carbon adhesion locally affects the pushing load both positively and negatively. Small carbon deposits filling the surface depressions lower the pushing load. In contrast, excess carbon growth creating a protrusion shape occasionally behaves as a resisting force during pushing. This study is performed to elucidate the influence of the carbon-covered area on the pushing load. Chamber wall images were gathered at operating coke plants by means of an inspection apparatus, which was inserted into the high-temperature chambers. An image processing technique was devised for classifying the wall surface into three states: bare brick, dense carbon, and patchy carbon. It was confirmed that the dense carbon has the optimum amount for suppressing high pushing loads. Statistical analysis using a probability model demonstrated that stable pushing can be obtained in specific dense and patchy carbon amounts.
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  • Improvement of Iron Ore Sintering Productivity by Redistributing Air Volume during Sintering Process

    pp. 74-82

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    DOI:10.2355/isijinternational.ISIJINT-2021-160

    The air volume distribution is one of the important factors of iron ore sintering speed and sinter strength, which plays an important part in achieving a high sintering productivity. The sintering process can be divided into two stages at the time of over-wetting layer disappearance. Increasing the air volume before the over-wetting layer disappears (1st stage) can improve the iron ore sintering speed. Decreasing the air volume after the over-wetting layer disappears (2nd stage) is beneficial to increase the sinter strength. When the air volume is redistributed to the air volume of 1st stage accounting for 74.59% and the air volume of 2nd stage accounting for 25.41%, the productivity coefficient increases from 1.34 t/(m2·h) to 1.46 t/(m2·h) with an increase of 8.96%, and the tumbler index of sinter reaches 59.96%. The sintering combustion layer thickness of 1st stage increases and the sintering combustion layer thickness of 2nd stage decreases in variable air volume sintering process. The moving speed of sintering combustion layer in variable air volume sintering process is significantly greater than that of the benchmark sintering combustion layer.
  • Effect of BaO on Formation Mechanisms of Silico-ferrite of Calcium and Aluminum

    pp. 83-90

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    DOI:10.2355/isijinternational.ISIJINT-2021-240

    Silico-ferrites of calcium and aluminum (SFCA) are formed during the sintering process, and their changes are critical to the quality of the sinter. Aiming to further clarify the effect of BaO (0 mass%, 1 mass%, 2 mass%, 3 mass%, 5 mass%, 7 mass%, and 9 mass%) on the bonding process of SFCA. In this work, X-ray diffraction (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), thermogravimetry-differential scanning calorimeter (TG-DSC) were used to analysis the formation mechanisms of SFCA. The results indicated that the main bonding phase was SFCA. In addition, SFCA-I, CF, C2F, and silicate existed in the BaO-free sinter. Adding a small amount of BaO (up to 2 mass%) could increase the decomposing temperature of SFCA and increase the formation of the needle-like SFCA. With the increase of BaO adding from 2 to 9 mass%, the BaFe12O19 (FB) formed could reduce the decomposing temperature of SFCA, which deteriorated the quantity of sinter. And, BaO can promote the formation of C2F in the CF and C2F system, which decreased the eutectic melting temperature of CF and C2F.
  • Pressure Drop and Gas Flow of Cohesive Zone in Oxygen Blast Furnace Using a Combination of Experimentation and Porous Model

    pp. 91-98

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    DOI:10.2355/isijinternational.ISIJINT-2021-237

    The top gas recycling and oxygen blast process (TGR-OBF), an alternative idea basing on modified traditional Blast Furnace (TBF) process, has been proposed and investigated for several decades. One of its remarkable environmental advantages is the extreme lower coke rate. A porous media model combined with softening and melting experimentation is developed to analyse the pressure drop and gas flow pattern in and around cohesive zone of this process. When the inlet velocity is 5 m/s, despite of more cohesive ore layers included, the pressure drop of cohesive zone in TGR-OBF is about 90 kPa in total, the same as the TBF’s. It shows that the permeability of cohesive zone is qualified for the steady operation in TGR-OBF process as conventional BF process.
  • Effect of Grinding Behavior on Liberation of Coal Macerals

    pp. 99-103

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    DOI:10.2355/isijinternational.ISIJINT-2021-209

    Macerals are the smallest organic constituents of coal. Reactive macerals or vitrinite is mainly responsible for coking potential of a coal during carbonization method. The effect of a novel grinding on coal maceral separation is studied in this work. The alternate method is based on grinding of coals by shearing compared to impact crushing as in other conventional methods like hammer mill. It is found that liberation of vitrinite is better in shearing. Coking properties of such maceral enriched coals showed improvement in laboratory coke making tests.
  • Impact of Solid Particles and Liquid Droplets on Foams – Cold Model and High Temperature Experiments

    pp. 104-111

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    DOI:10.2355/isijinternational.ISIJINT-2021-226

    In order to obtain a realistic view of the foam in metallurgical slag, high temperature experiments where the foaming heights of FeO–CaO–SiO2–MgO slags containing precipitated MgO∙FeO particles were measured. The foaming height slightly increased when small amounts of particles were present in the slag, but decreased to half height already when approximately 8 vol% particles were present in the liquid phase of the foam. To help the understanding, the foaming heights of silicone oil and food oil containing liquid insoluble droplets and non-reacting particles were also studied at room temperature. In these experiments, insoluble oil droplets were found to stabilize the foam, increasing the foaming height, while the addition of water droplets or solid particles had very little effect on foaming height. In line with the literature, it is believed that the interfacial energy between the droplets or particles and the bulk liquid as well as the interfacial energy between the droplets or particles and gas plays an important role. When the interfacial energy between the different phases becomes too high, the foaming height decreases, while when it’s low enough, the foaming height increases.
  • Fluid Flow and Mixing Phenomena in Mechanically Agitated and Gas Stirred Ladle Systems and Their Comparisons

    pp. 112-123

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    DOI:10.2355/isijinternational.ISIJINT-2021-276

    A sliding mesh-based LES (large eddy simulation) mathematical model has been developed to investigate fluid flow and mixing phenomena in a mechanically agitated (MA) water model ladle (D = 0.30 m) fitted with an impeller/paddle. Parallel to such, liquid velocity and 95% bulk mixing times were experimentally measured as a function of rotational speed of the impeller. These were applied to validate mathematical model predictions. On the basis of results derived from the present physical and mathematical modelling investigation and already published data on gas stirred (GS) ladle systems, a performance comparison between mechanical and gas agitated systems has been presented. It is shown that at specific stirring power, similar to those practised in ladle refining (~10−3 W/kg), while intensity of motion is more pronounced and mixing is considerably faster, corresponding flow establishment periods are relatively longer in the mechanically agitated system. Furthermore, while relationship between mixing time – specific stirring power in both the systems are found to be very similar e.g., τmix,95%,MA[ This part of text is omitted ] vs. τmix,95%,GS[ This part of text is omitted ], markedly different and contrasting dependence of mixing time on liquid depths i.e., τmix,95%,MA∞H1.8 vs. τmix,95%,GS∞H−1.0 in the two systems have been observed. In addition to such, dynamic similarity criterion for mechanically agitated systems has been investigated and it is demonstrated that similar to gas stirred ladle systems, a Froude based modelling criteria suffices.
  • Cleanliness and Control of Inclusions in Al-Deoxidized Bearing Steel Refined by Basic Slags during LF-VD-Ar Bubbling

    pp. 124-132

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    DOI:10.2355/isijinternational.ISIJINT-2021-306

    Cleanliness and control of inclusions in Al deoxidized bearing steel were studied by industrial trials, in which three basic slags were used in the LF-VD-Ar bubbling refining process. With basicity (mass ratio of CaO/SiO2) about 3.9–4.2, 5.2–6.5 and 6.9–7.1 while Al2O3 about 30.9–32.5 mass%, 37.2–40 mass% and 29.8–30.4 mass%, T.O content in steel after Ar bubbling was 0.0006 mass%, 0.0007 mass% and 0.0004 mass%, respectively. During the refining, inclusions experienced the evolution from Al2O3 into spinel and finally into CaO–MgO–Al2O3. By comparison, inclusions were more desirably controlled when slag basicity and Al2O3 contents were about 6.9–7.1 and 29.8–30.4 mass%, with lowest number density, smaller sizes within 20 µm and average composition in liquid region. Particularly, after Ar-bubbling, pick-ups in the number density of inclusions were observed for the three heats of trials and large inclusions (even exogenous inclusions over100 µm) were often seen in heat 2. The obtained results prompted the risk of large inclusions in bearing steel in Ar bubbling, which were detrimental to fatigue lives of bearing.
  • Relationship between Inclusions and Internal Defect Spatial Distribution in Large Forging Piece for Wind Power Generation Gear

    pp. 133-141

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    DOI:10.2355/isijinternational.ISIJINT-2021-356

    The spatial distribution of inclusions in a large forging piece is closely related to the fatigue life of gears. In this paper, the size, number, types, and distribution of inclusions in a large forging piece of gear steel used for wind-power generation have been systematically analyzed by the automatic scanning of inclusions, in situ analysis of inclusions, scanning electron microscopy, and energy spectrum analysis. The inclusions distribution model is established and the size of the largest inclusion in the forging piece is predicted. The distribution of the number and size of inclusions exhibits an exponential relationship. The total number of inclusions is lowest at the tooth center area, and macro-inclusions with sizes above 10 µm mainly concentrate in the tooth center, with a maximum size of 101.5 µm. The typical inclusions in forging pieces include 2.85% oxides, 80.95% sulfides and 16.2% composite inclusions of oxides and sulfides. The sulfide preferentially precipitates on the surface of oxide’s core in the following order: Al2O3–MgO–CaO > Al2O3 > Al2O3–MgO > Al2O3–MgO–SiO2–CaO > Al2O3–MgO–SiO2 > Al2O3–SiO2. It is helpful to change the brittle oxides into composites of oxides and sulfides to improve the fatigue life of gear steel.
  • Numerical Investigation for the Influence of Turbulent Heat Transfer of Mushy Zone on Shell Growth in the Slab Mold

    pp. 142-148

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    DOI:10.2355/isijinternational.ISIJINT-2021-225

    The turbulent heat transfer in the mushy zone caused by the impinging of molten steel jets in the slab mold has a significant effect on the growth of the solidified shell and the formation of impinging zone, as well as the quality of steel products. In the present work, a Peclet number of the mushy zone (Pem) is proposed to analyze the influence of turbulent heat transfer on the shell growth in the mushy zone and define the boundary of the impinging zone. A three-dimensional mathematical model based on the enthalpy-porosity method has been established to predict the flow, heat transfer and solidification processes in the slab mold. The influences of casting speed and secondary dendrite arm spacing (SDAS) on the turbulent heat transfer behavior are also investigated. The results indicate that the turbulent heat diffusion has a great effect on the formation of the impinging zone and is the only source of energy to maintain the boundary of the impinging zone. The Pem can evaluate the turbulent heat transfer in the mushy zone and is a more reasonable method to obtain a clearer boundary of the impinging zone. The impinging zone is formed when the Pem reaches a critical value, been dependent on the casting speed and SDAS.
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  • Effect of Spray Pressure and Height on Interfacial Heat Transfer of H13 Steel during Spray Cooling

    pp. 149-156

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    DOI:10.2355/isijinternational.ISIJINT-2021-248

    To accurately calculate mold temperature field during spray process of die casting process, the interfacial heat transfer coefficient (IHTC) between the mold and the spray medium is an extremely important thermo-physical parameter. In this paper, a spray experiment was conducted with different spray pressures and heights, in which the temperature history throughout the spray cooling process of H13 steel plate was recorded. The IHTC under the different spray parameters were calculated by utilizing the nonlinear estimation method. The interface morphology and heat transfer characteristics within the spray cooling process were studied, and the influence of spray pressures and heights on the IHTC was discussed. The results show that the interface can be divided into wet and dry regions, where the former significantly affects the heat transfer behavior on the interface. It is found that high spray pressure has a positive effect on improving peak IHTC whereas it impedes the expansion of wet region and delays the peak of IHTC; reducing spray height leads to the expansion of wet region and the rise of peak IHTC.
  • An Operator Behavior Model for Thermal Control of Blast Furnace

    pp. 157-164

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    DOI:10.2355/isijinternational.ISIJINT-2021-073

    To realize precise thermal control of a blast furnace, an operator model that imitates the behavior of skilled operators was developed using a convolutional neural network (CNN). Conventional thermal control systems suffer from large control errors when large disturbances occur, e.g., when low-quality materials are used. Despite these adverse conditions, capable operators are still able to take appropriate control actions by making the best use of sensor information. Such operators’ control actions were simulated by the CNN, and the validation results showed that the accuracy of the developed operator model was 71%. The operator model was then incorporated in the operation guidance system at actual furnaces. It was found that the operator model can cope with the severe situations where the material characteristics change or abnormal descent of the burden materials occurs.
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    1. Behavior of Carbon Adhesion on Aged Coking-chamber Walls to Pushing Load ISIJ International Vol.62(2022), No.1
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  • Development of New Inspection Method for LSAW Pipes Using Matrix Phased Array UT

    pp. 165-172

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    DOI:10.2355/isijinternational.ISIJINT-2021-293

    A new method was developed for inspection of welds in LSAW (Longitudinal Submerged Arc Welded) steel pipes using ultrasonic testing. Defects called I.P. (Incomplete Penetration) may occur in the central part of the wall thickness in welds of LSAW steel pipes, and these defects have a flat shape in the thickness direction. In order to detect these defects with high sensitivity without influence of the welded part shape, transmission of the ultrasonic wave perpendicular to the defect at a high refraction angle is effective. On the other hand, there were also problems in use of the angle beam method with a high refraction angle, including a decrease the sensitivity of ultrasonic testing and the need to maintain the angle accurately. In the new method proposed here, a sector scan with a line focus beam using matrix phased array UT was adopted, securing high sensitivity and stability in inspections. It’s characterized by using a matrix array probe in which the small vibrators are arranged so that the width of small vibrators gradually decreases from the center of the matrix probe toward the outside. In the verification test using the actual steel pipes, good result was obtained with a S/N ratio of 24 dB or more and good repeatability for a flat bottom hole with 3 mm diameter that is simulated I.P.. The operability of probe setting is also better than tandem method because only one probe is used and the incident angle can be adjusted by the phased array technology.
  • Characterization of Deformation by Cold Rolling in Ferritic Steel Containing Cu Particles Using Neutron Transmission Analysis

    pp. 173-178

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    DOI:10.2355/isijinternational.ISIJINT-2021-144

    Neutron transmission spectra of Fe-2 mass% Cu alloy (Cu steel) were measured to characterize the changes of crystallographic texture of ferrite grains and nanostructure of dispersed Cu particles with cold rolling. Bragg edges appearing in the neutron attenuation coefficient of as-aged Cu steel show a sawteeth pattern corresponding to random texture. With increasing equivalent strain, the 110 Bragg edge changes to a peak and the 200 Bragg edge becomes sharp. These changes indicate the rotation of {110} planes toward a tilt angle of 32° to the rolling plane and the increase in the fraction of the {100} planes in the rolling plane. This can be explained by the evolution of <111>//ND, <322>//ND, and <100>//ND preferred orientations with the cold rolling, where ND denotes the normal direction. In the wavelength range longer than 0.4 nm, the neutron attenuation coefficient increases due to a small-angle neutron scattering (SANS) contribution from dispersed Cu particles in the matrix. Comparing the experimental results with simulation, the change in the SANS contribution indicates that the dispersed Cu particles are elongated with the cold rolling. These results demonstrate that the neutron transmission analysis is useful for microstructural characterization of steels and the sequential change of the microstructures.
  • Vertical Vibration Characteristics of Strip Rolling Mill under Compound Roll Bearing Failure

    pp. 179-190

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    DOI:10.2355/isijinternational.ISIJINT-2021-193

    A vertical vibration model of a 3-DOF strip rolling mill with a compound roll bearing failure on the outer raceway and inner raceway is established. Through MATLAB simulation, the vertical vibration characteristics of the strip mill work roll are compared and analyzed under the condition that the outer raceway failure of the roller bearing remains unchanged, the inner raceway failure changes and the inner and outer raceway failures change simultaneously. It provides a certain theoretical basis for further clarifying the non-linear vibration mechanism of the rolling mill caused by the compound bearing failure. At the same time, when the internal and external raceways of the roller bearing have a compound failure, the effects of different roller numbers and contact angles on the vibration displacement fluctuations of the work roll are analyzed, which has certain theoretical guidance for the optimization design of the roll bearing.
  • Material Modeling of Hot-Rolled Steel Sheet Considering Differential Hardening and Hole Expansion Simulation

    pp. 191-199

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    DOI:10.2355/isijinternational.ISIJINT-2021-365

    The elastoplastic deformation behavior of a 440-MPa hot-rolled steel sheet subjected to many linear stress paths is precisely measured using biaxial tensile tests with cruciform specimens (ISO 16842: 2014) and multiaxial tube expansion tests to determine appropriate material models for finite element analysis (FEA). It is found that the Yld2000-2d yield function correctly reproduces the contours of plastic work and the directions of the plastic strain rates. Differential hardening (DH) models are determined by varying the values of the exponent and material parameters for the Yld2000-2d yield function as functions of the reference plastic strain. Moreover, a finite element analysis of hole expansion in the test material is performed. The DH model correctly predicts the minimum thickness position, which matches the fracture position of the specimen in the experiment.
  • Comparison of Laser Power and Scan Speed in SLM

    pp. 200-208

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    DOI:10.2355/isijinternational.ISIJINT-2020-674

    With the rapid development of selective laser melting technology, the effect of different process parameters on the quality of the printed parts was studied by many researchers in recent years. In this work, a comparison on the effect of laser power and scan speed which was considered as two main factors to affect laser power density, was studied. An inner structure part with overhanging surface was designed and printed to better study the influence on the surface quality caused by these two factors. The testing results revealed that with the same energy density, different performance can be observed on the overhanging and side surface quality caused by laser power and scan speed. With the increasing of the laser power, side surface roughness value showed an increasing trend due to the increasing of the temperature gradient of the molten pool while the overhanging surface quality had a descending trend. It was mainly due to the fact that to keep the same laser power density, the scan speed decreased which resulted to the increasing time for solidification of the molten pool. This phenomenon lead to the increasing of the sinking distance and the overhanging surface quality showed a decline trend.
  • Hardening Behavior in Diffusion Zone of Fe–Mn and Fe–Cr Binary Alloys Nitrocarburized after Cold Working

    pp. 209-217

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    DOI:10.2355/isijinternational.ISIJINT-2021-217

    To clarify the effect of dislocation on the precipitation behavior of nitrides, Fe–Mn and Fe–Cr binary alloys were deformed, nitrocarburized, and examined their hardening behavior. We measured the content of N in a diffusion layer and estimated the amount of alloy nitrides based on the measured N content. With the Fe–Cr alloy, the deforming have little effect on the hardness and CrN precipitation behavior. With the Fe–Mn alloy, the deforming contributes to increase in hardness with denser and finer Mn3N2 precipitation. Transmission electron microscopy observation shows CrN precipitates mainly by homogeneous nucleation but Mn3N2 precipitates mainly on dislocation. The thermodynamic calculation shows that substitutional alloy element (M) and N can form M–N clusters in Fe–Mn–N and Fe–Cr–N systems through phase separation of bcc lattice. Because Cr–N clusters have a higher nucleation driving force than Mn–N clusters, they can be formed by homogeneous nucleation. We evaluated the degree of the precipitation hardening and revealed that CrN has a larger hardening ability per unit precipitation amount than Mn3N2.
  • Wear and Corrosion Resistance of CrN Films on Oxynitriding-treated Vanadis 8 Tool Steel via the DC Magnetron Sputtering Process

    pp. 218-226

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    DOI:10.2355/isijinternational.ISIJINT-2021-318

    This research coated CrN films on oxynitriding-treated Vanadis 8 tool steel using the DC magnetron sputtering process of the PVD technique. The experimental parameters include different gas flow rates (Ar/N2 was 20/20, 24/16, 28/12, and 32/8, respectively), with a bias of −50 V, power of 100 W, deposition temperature of 300°C, and deposition time of 180 min, respectively. The experimental results show that Vanadis 8 tool steel can form an effective oxynitriding layer with a depth of about 50 µm after the oxynitriding treatment, and the surface hardness increased to about 1400 HV0.05. Furthermore, the duplex coating layers exhibited optimal properties when the CrN films treated at an appropriate gas flow rate of Ar/N2 was 24/16. Meanwhile, according to XRD analysis, the coating layer has a relatively high content of CrN composition, as well as the best wear resistance (the lowest specific wear rate when the loads of 2 N and 4 N were 2.05 × 10−5 and 1.56 × 10−5 mm3·m−1·N−1) and good corrosion resistance (in a 3.5 wt% NaCl environment, Icorr = 3.05 × 10−4 A·cm−2, Rp = 362.52 Ω·cm2). Overall, this study reveals that the CrN/oxynitriding duplex surface treatment could effectively improve the wear and corrosion properties of Vanadis 8 tool steel.
  • Effect of Cold-rolling and Heating Rate on Austenite Formation in a Low–Carbon Steel

    pp. 227-236

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    DOI:10.2355/isijinternational.ISIJINT-2021-294

    The austenite formation kinetics of a low–carbon steel under two initial conditions—annealed and cold–rolled (0.08C–1.22Mn–0.73Si) were determined by dilatometric analysis during continuous heating. In both conditions, the austenite formation occurred in two stages. The critical transformation temperatures are a function of the heating rate but not of the initial microstructure (annealed or cold–rolled) that is, for a given heating rate (0.06, 0.36, or 0.66 K s−1), the critical transformation temperatures are similar for both conditions, despite in the cold–rolled condition, the cementite is spheroidized prior the austenite formation. The volume fraction of austenite was fitted based on the Johnson–Mehl–Avrami–Kolmogorov model to calculate the kinetics parameters k and n. The parameter k is proportional to the heating rate, and n changes between stages and heating rates for both conditions suggesting variations in the nucleation mode. The austenite–formation rate was calculated as a function of the microstructural evolution and transformation time. The austenite formation rate in the first stage is lower in the cold–rolled steel, during a specific range of temperatures, than in annealed steel which presented a formation rate maximum at a peak temperature. In the second stage, the behavior was similar for both conditions with a peak at the rate maximum.
  • Modeling Dissolution of Vanadium Carbide and Carbonitride in Fe–C–V(–N) Austenite

    pp. 237-246

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    DOI:10.2355/isijinternational.ISIJINT-2021-340

    A computer model is constructed to simulate the dissolution of V carbide and carbonitride with size distribution in steels. Assuming local equilibrium of carbon, nitrogen, and V at the particle/matrix interface, the dissolution rate is calculated using the mean-field and invariant field approximations. The fraction of particles and size distribution (PSD) of V carbide are in good agreement with those in an Fe–C–V alloy reported in the literature. The V mass fraction and PSD of carbonitride, measured by extraction replica in this study, were also reproduced well by simulation in an Fe–C–V–N alloy (N~20 ppm). Moreover, simulation with an equilibrium tie-line passing through the bulk alloy composition, as often done in the calculation of precipitate dissolution rate, yielded a large error.
  • V-Bendability of Ultrahigh-Strength Low Alloy TRIP-Aided Steel Sheets with Bainitic Ferrite Matrix

    pp. 247-256

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    DOI:10.2355/isijinternational.ISIJINT-2021-092

    Effect of retained austenite characteristics on V-bending in ultrahigh-strength TRIP-aided steel sheets with bainitic ferrite matrix (TBF steel) was investigated for automotive applications. V-bending tests were performed on a servohydraulic testing machine at a processing speed of 1 mm/min using a 88-degree V-punch (2.0 mm in punch radius), 88-degree V-die (12 mm in die gap, 0.8 mm in die shoulder radius), and a rectangular specimen (50 mm in length, 5 mm in width, 1.2 mm in thickness). The results are summarized as follows.(1) The 0.2C-1.5Si-1.5Mn (mass%) TBF steel sheets were able to perform V-bending by strain-induced martensitic transformation of TRIP effect. On the other hand, ferrite-martensite dual-phase (MDP0) steel sheet of 900 MPa grade was not able to perform 90-degree V-bending because of initiation of crack in tension area.(2) The TBF375 steel sheet that produced by heat treatment of annealing at 1173 K (900°C) for 1200 s followed by austempering at 648 K (375°C) for 200 s, of 1100 MPa grade was able to enable the 90-degree V-bending that considered an amount of springback (Δθ=θ1θ2), in which the θ1 and the θ2 were a bending angle on loading and a bending angle after unloading respectively, of more than 2-degree by controlling a displacement of punch bottom dead center.
  • Feasibility Study of Visualizing Strain Distributions Using Opal Film

    pp. 257-262

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    DOI:10.2355/isijinternational.ISIJINT-2021-383

    This paper presents a feasibility study of visualizing the strain distribution of structural elements using opal film. Opal film with an initial peak wavelength of 510 nm was employed in tensile and four-point bending tests to evaluate the feasibility of visualizing the strain distribution using this type of film. The experimental results of the tensile and four-point bending tests show that the peak wavelength has a linear relationship with the first invariant of the strain. The slope of the experimentally obtained relationship between these variables showed good agreement with the theoretically predicted slope. In the four-point bending test, visualization of the first invariant of the strain using opal film was successfully demonstrated, thereby confirming the feasibility of strain visualization using opal film.
  • Kinetics of Calcium Leaching from Particulate Steelmaking Slag in Acetic Acid Solution

    pp. 263-274

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    DOI:10.2355/isijinternational.ISIJINT-2021-121

    In order to reduce CO2 emission, the CO2 sequestration using particulate steelmaking slag in water is world widely being studied through a Ca-carbonation method. As consequence, the improved efficiency of Ca leaching from the steelmaking-slag particles contributes significantly to increasing the amount of fixed CO2. Therefore, in this study, for the purpose of understanding the Ca leaching from steelmaking slag particles, the rate of Ca leaching in week acidic solution was analyzed by several leaching kinetics models such as the shrinking core model and the logarithmic rate law. In addition to Ca, the leaching rate of Fe which is one of the major elements was also investigated. The Ca and Fe leaching process with stirring could be fitted well by logarithmic rate law. Moreover, by the observation using SEM-EDX, it was observed that the residue after acetic acid leaching was porous material with the pores blocked. From these results, it was revealed that the mass transfer in the products blocking the pore surface of slag particles was very likely to be the rate-controlling step of Ca leaching. In fact, promoting mass transfer by ultrasonic irradiation could enhance the rate of Ca leaching remarkably. While the Ca leaching ratio reaches 56.6% at 300 min without ultrasonic irradiation, the leaching ratio reaches 57.3% just for 30 min leaching with ultrasonic irradiation. This study reveals that promoting the mass transfer in the products blocking the pore surface of slag particles is important for increasing the rate of Ca leaching.
  • Thermal Diffusivity and Conductivity of Fe3O4 Scale Provided by Oxidation of Iron

    pp. 275-277

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    DOI:10.2355/isijinternational.ISIJINT-2021-326

    The thermal diffusivity and conductivity of Fe3O4 scale have been determined with the laser flash method. Fe3O4 scale was provided by oxidation of iron plates at 823 K in Ar containing 0.84%H2 and 15.6%H2O. The scale was characterized by scanning electron microscopy and X-ray diffraction analysis for high temperature use to identify the phase of the scale. The thermal diffusivity and conductivity derived for the Fe3O4 scale decrease from 1.1 × 10−6 m2s−1 to 4.1 × 10−7 m2s−1 and from 3.5 Wm−1K−1 to 1.7 Wm−1K−1, respectively, with increasing temperature from room temperature to 676 K. The effective thermal conductivity of iron oxide scale with Fe3O4 has been evaluated assuming that Fe3O4 occupies 30% of the total scale thickness, suggesting the impact of the presence of Fe3O4 is about ten percent.
  • Verification of Thermodynamic Models for Predicting Grain Boundary Segregation of Carbon and Nitrogen in Ferritic Steels

    pp. 278-280

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    DOI:10.2355/isijinternational.ISIJINT-2021-386

    The concentrations of C and N segregated at the grain boundaries (GB) in Fe–C, Fe–N binary alloys, and Fe–C–N ternary alloys were calculated using the McLean and the Hillert-Ohtani models. Comparison of the calculated data with experimental values obtained by three-dimensional atom probe tomography (3DAP) revealed that the experimental values were roughly explained by the Hillert-Ohtani model for the binary alloys. The McLean model also can predict similar results when the fraction of available sites in the GB layer is assumed to be saturated at 0.1. On the other hand, the Hall-Petch coefficient (ky) of Fe–C–N, determined from tensile tests, was linearly related to the predicted concentrations of segregated C and N. Proposedly, ky can be predicted from the chemical composition and heat treatment temperature via thermodynamic calculations.
  • Contents and Publication Data

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