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

ISIJ International Vol. 53 (2013), No. 10

  • Enhanced Quality in Electric Melt Grey Cast Irons

    pp. 1683-1695

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    DOI:10.2355/isijinternational.53.1683

    The paper reviews original data obtained by the authors, recently disconnected published, concerning the specific solidification pattern of low S (<0.05%) irons, with very low Al (<0.005%), melted and superheated in acid lined, coreless induction furnaces, and how superheating affects the iron quality with effective metallurgical treatments for use in these conditions. Solidification undercooling increased with increasing superheat, associated with significant changes in chemical composition, such as C, Si, Mn, Al and Zr, involved in the nucleation of graphite. The concept in the present paper sustains a three-stage model for nucleating flake graphite [(Mn,X)S type nuclei]. There are three important groups of elements [deoxidizer/Mn, S/inoculating] and three technology stages in electric melt iron [superheat/pre-conditioning base iron/final inoculation]. Different materials were used for pre-treatment of the iron melt, to control oxidization levels and/or to promote active graphite nucleation sites, including carbon materials and metallurgical silicon carbide. Special attention was paid to maintain Al and Zr recoveries in the melting furnace for their effects on the iron structure. A double treatment utilizing strong oxide forming elements, such as Al and Zr for preconditioning, followed by inoculation decreased eutectic undercooling parameters. This treatment improved graphite characteristics and avoided carbides. For foundry application, it is recommended to ensure (Mn,X)S compound formation, compatible for nucleating graphite with less eutectic undercooling. Attention is drawn to ensuring a control factor (%Mn) × (%S) equals 0.03 – 0.06, accompanied by 0.005–0.010% Al and/or Zr content in inoculated grey irons.
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  • Influence of Basicity and TiO2 Content on the Precipitation Behavior of the Ti-bearing Blast Furnace Slags

    pp. 1696-1703

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    DOI:10.2355/isijinternational.53.1696

    The present paper investigated the influence of basicity and TiO2 content on the crystallization behavior of the Ti-bearing blast furnace slag (Ti–BF slag). Single Hot Thermocouple Technique (SHTT) was applied to construct the Time-Temperature-Transformation (TTT) diagrams. Scanning Electron Microscope equipped with Energy-Dispersive X-ray spectroscope (SEM-EDX) and X-Ray Diffraction (XRD) were employed to observe the morphology and determine the crystalline phase of the Ti-enriched crystals. It was found that rutile was formed as the Ti-enriched phase when the basicity of the sample was lower than 0.6, and perovskite appeared as the Ti-enriched phase with an increasing basicity to 1.0. It was also noticed that the addition of TiO2 could decrease the incubation time in the TTT diagram of the samples. The kinetics of the formation of Ti-enriched crystals, rutile and perovskite, was studied, and the mechanism of crystallization and growth was further discussed. The results indicated that the crystallization of rutile was one-dimensional interface-controlled growth, and the nucleation rate varied with the holding time at different TiO2 content. While the precipitation behavior of perovskite was three-dimensional diffusion-controlled growth, and its nucleation rate decreased with the holding time.
  • Behaviors of the Molten Copper Slags in the Vertical Electric Field

    pp. 1704-1708

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    DOI:10.2355/isijinternational.53.1704

    The behaviors of molten copper slag under the vertical electric field were investigated in this paper. The presence of the electric field could accelerate the migration of copper drops from anode region to the cathode. Electrolysis reaction of molten copper slag was occurred at the interface of electrode and the molten slags. The copper slag cleaning process would be promoted in the electric field due to the electrocapillary and a certain degree of electrolysis. The Physical and chemical processes of copper slag cleaning under the vertical electric field was also summarized in the article.
  • Equilibrium Distribution Ratio of Phosphorus between Solid Iron and Magnesiowustite-saturated Al2O3–CaO–FetO–MgO–SiO2 Slag at 1623 K

    pp. 1709-1714

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    DOI:10.2355/isijinternational.53.1709

    In the conventional iron-making process, the oxygen potential in the hearth of the blast furnace is determined only by the temperature because of the carbon-saturated conditions. As a consequence, impurities such as phosphorus are reduced and dissolved in the iron because of the excessively low oxygen partial pressure. The oxygen partial pressure can be controlled by using gas reductants such as hydrogen and carbon monoxide. Under these conditions, solid iron is obtained because of the low carbon content. In this study, the equilibrium distribution of phosphorus between the solid iron and molten slag is investigated at 1623 K as functions of the oxygen partial pressure and the basicity of the slag. The experimental results show that the phosphorus content in the solid iron is sufficiently low under the experimental conditions employed. The phosphate capacity is also evaluated, and a regression equation is obtained by comparing the results with those of previous studies.
  • Influence of Slag Basicity and Temperature on Fe and Mn Distribution between Liquid Fe–Mn–Ca–O–S Matte and Molten Slag

    pp. 1715-1724

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    DOI:10.2355/isijinternational.53.1715

    We have proposed a novel process for recycling Mn wasted in steelmaking slag via sulfurization to separate P from Mn. For clarifying the efficient recovery of Mn from steelmaking slag, the influences of slag basicity and temperature on the distributions of Mn and Fe between the Fe–Mn–Ca–O–S matte and FeO–MnO–MgO–P2O5–SiO2–CaO slag were investigated. The distributions of Fe and Mn between the matte and the slag increased with an increase in the slag basicity. Moreover, when log PS2 (PS2: partial pressure of S) was more than −2, the Mn distribution increased to be more than 10 as the slag basicity increased beyond 1.7. Even though the effects of slag basicity and PS2 on the Mn content in the matte were small, the behavior of Mn in the matte was dependent on temperature. In order to understand the behavior of Mn and Fe in steelmaking slag and matte, the relationship between the activity coefficient ratio of MnS and FeS (γMnS/γFeS) and the mole fraction ratio of MnS and FeS for the matte was investigated. To evaluate γMnS/γFeS for the matte, the activity coefficient ratio of MnO and FeO (γMnO/γFeO) was estimated using an empirical formula and the RS model, and the mole fractions of MnS and FeS in the matte were calculated on the basis of mass balance. The results revealed that the values of γMnS/γFeS for the Fe–Mn–S–O matte were about twice those for the Fe–Mn–Ca–S–O matte. Moreover, γMnS/γFeS for the Fe–Mn–Ca–S–O matte decreased with an increase in temperature.
  • Effects of Valence Control of Iron Ions on Radiative Heat Transfer in Mould Flux

    pp. 1725-1731

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    DOI:10.2355/isijinternational.53.1725

    The present study aims to investigate the possibility of reduction of radiative heat flux in the continuous casting process by valence control of iron ions in mould flux. The compositions of samples were designed on the basis of a practical mould flux, where the basicity defined as CaO/SiO2 was also varied from 0.6 to 1.4 to change the valence of iron ions. Mixtures of oxide and fluoride powders were melted in platinum crucibles in air and then the melts were quenched into brass moulds to obtain glassy samples. In addition, graphite crucibles were also used to melt samples having the basicity of 1 at lower partial pressure of oxygen. Some glassy samples were heat-treated for crystallisation. Glassy and crystallised samples were subjected to chemical analyses and optical measurements of apparent reflectivity and transmissivity. The concentration ratio of Fe3+/Fe2+ increased with increasing basicity but decreased by melting in graphite crucibles. Increasing concentration ratio of Fe3+/Fe2+ leads to an increase of radiative heat flux for the glassy samples but to a decrease for the crystallised samples: the effect of valences of iron ions is more prominent in the glassy samples. In the crystallised samples, on the contrary, the degree of crystallinity affects radiative heat flux more strongly than the valence of iron ions.
  • Quantification of Moisture Contents in Iron and Manganese Ores

    pp. 1732-1738

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    DOI:10.2355/isijinternational.53.1732

    The moisture contents of several synthetic and natural goethite-bearing samples were determined by the loss-of-mass method and by the Karl-Fischer titration. It was found that drying at 105°C did not remove all the water from these samples, and that temperatures above 200°C would be required to completely remove the adsorbed water. The multiple peaks observed in the TGA and DSC measurements are not due to the dehydroxylation of goethite, but are due to the release of adsorbed water. The decomposition of goethite into hematite occurs with the release of adsorbed water from room temperature up to the onset of the main dehydroxylation peak. The dehydroxylation occurs in a broad range of temperatures due to the existence of a particle-size distribution, surface hydroxyls and formation of a hematite coating. The determination of all adsorbed water is best performed by adding the powdered sample into the Karl-Fischer reaction vessel.
  • Quantitative Evaluation for Relationship between Development of Pore Structure and Swelling of Coal in Carbonization of Single Coal Particle

    pp. 1739-1748

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    DOI:10.2355/isijinternational.53.1739

    The objective of this paper are to study the formation process of coke pore structure in relation to the swelling of coke during the thermoplastic stage and the pore structure at the initial carbonization. The swelling ratio, changes in pore structure and growth behavior of pore which originally present in the coal were evaluated. Two kinds of caking coals were carbonized in nitrogen-atmosphere with an infrared furnace. The swelling ratios were measured, and the cross-sectional images of coal particles at different heating temperatures were observed with an optical microscope. Before carbonization, all pores in both coals were a diameter of less than 100 μm. When the temperature increased up to the level at which the swelling started, the pores with greater than 100 μm-diameters were formed, and they had also simultaneously coalesced. However, each coal had a different temperature for starting swelling and observing the generation and coalescence of pores with a diameter of more than 100 μm. At this point, the formation of pores were expressed with Laplace equations. The results showed the volatile matter inflow affected the change of pore structure. Furthermore, the pore structures within coal particles before and after carbonization were compared by micro-X-ray Computed Tomography. Carbonization up to the temperature for the softening stage increased pore diameters, which provided evidence that the proportion of pores existing within post-carbonized coal had grown based on the pores already existing in pre-carbonized coal.
  • Reduction of Iron Ore/Empty Fruit Bunch Char Briquette Composite

    pp. 1749-1755

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    DOI:10.2355/isijinternational.53.1749

    Utilization of Malaysian low grade iron ore is an attractive option of domestic iron resource; however, extra energy consumption is required and thus contributes to greenhouse gases. In this study, incorporation of low grade iron ore deposits with oil palm waste as substitution of coke was studied. Briquette composites of iron ore and char derived from oil palm empty fruit bunch (EFB) pyrolysis were produced with minute amount of distilled water. Reduction processes were carried out at 873 K to 1173 K under argon atmosphere in an electric furnace for briquette composites with different mass ratio of ore/char. For kinetic analysis, briquette with 8:2 ore/char ratio was used and reduction was carried out by varying the residence time. The percentage of reduction was estimated by oxygen removal and considering the weight loss. The structural and chemical changes of raw materials and briquettes were characterized using XRD, TG/DTA, and XRF. The results indicate that increasing in temperature, time and EFB char content in the briquette will increase the percentage of reduction. XRD and XRF results show that the original iron oxide hydrate has been transformed into partial wustite by several stages and the iron content increased up to 62.7 wt% for 6:4 ore/char ratio briquette. Kinetic results suggest that reduction of iron is controlled by gasification of carbon and the activation energy is 43.21 kJ. EFB char appears to be a promising energy source for replacing part of coal consumption in iron making, and reducing CO2 emission.
  • Flow Patterns of Iron and Slag in the Blast Furnace Taphole

    pp. 1756-1762

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    DOI:10.2355/isijinternational.53.1756

    The drainage of molten iron and slag is of considerable significance for the ironmaking blast furnace (BF). The draining process is in principle driven by the in-furnace overpressure that balances the pressure drops induced by liquid flows through the dead man and taphole. The two-liquid flow in the taphole has not received much attention, even though some investigators have mentioned the key role of taphole operation in BF drainage. In this paper, the taphole flow pattern, i.e., separated or dispersed flow, is predicted by utilizing a model of zero real characteristic which is based on the stability analysis of two immiscible liquids flowing through an upwards inclined tube. The model is firstly validated by comparison with a set of physical modeling results from the open literature and the experimental system is believed to represent that of an industrial BF taphole, according to similarity laws. Simulations with the model are applied to demonstrate how different factors affect the taphole flow pattern. In a more detailed application short-term tapping data from the commercial BF is evaluated by the model. The calculated results show that separated flow of iron and slag is more likely to occur in the taphole of the studied BF.
  • Quantitative Analysis on Contribution of Direct Reduction of Iron Oxide in Carbon Composite

    pp. 1763-1769

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    DOI:10.2355/isijinternational.53.1763

    Many reactions such as the reduction of iron oxide, gasification of carbon, and so on occur simultaneously during heating of the iron oxide–carbon composites which attract attention as “microreactors”. Solid carbon and CO gas react with iron oxide via direct and indirect reductions, respectively. The rate of indirect reduction has been studied extensively. On the other hand, there are very few reports on the quantitative analysis on the direct reduction due to analytical difficulties, although it is important to understand the total reduction mechanism in detail. In this study, the contribution of the direct reduction by solid carbon in the composite while heating at a constant rate under inert gas flow was quantitatively evaluated.
    The direct reduction from Fe2O3 to Fe3O4 proceeds at a low temperature during heating of the Fe2O3–graphite composite. When the reduction from Fe2O3 to Fe3O4 completes below 1000°C, the contribution ratio of the direct reduction in the total reduction is approximately 45%. However, there is no effect of the particle size of the raw materials on the contribution ratio. Further, the contribution ratio of the direct reduction for the reduction from Fe3O4 to FeO is small.
  • Effect of High Reactivity Coke for Mixed Charge in Ore Layer on Reaction Behavior of Each Particle in Blast Furnace

    pp. 1770-1778

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    DOI:10.2355/isijinternational.53.1770

    A low coke rate operation in blast furnace is desired to decrease the carbon input and mitigate global warming problem. However, low coke rate operation tends to cause the gas permeability to deteriorate. The mixing of small-size coke (nut coke) including high reactivity coke in ore layer is considered to be a promising way to improve permeability and increase reaction efficiency in a blast furnace. Although adding a nut coke mixing to an ore layer is predicted to be empirically effective in low coke rate operation, there is little actual data on microscopic phenomena of each particle in the packed bed. In the present study, an Euler–Lagrange approach was introduced to precisely understand the influence of the packed bed structure on the reaction behavior of each particle in the three-dimensional particle arrangement.
    It was observed that the heterogeneity on the reaction rate and temperature distribution was influenced by the particle arrangement. When high-reactivity coke was used at approximately 1273 K, although CO gas fraction increased, the gaseous phase temperature decreased due to the active solution loss reaction rate of the nut coke in the mixed layer. As a result, the ore reduction rate decreased. The contribution of high-reactivity coke to the ore reduction rate depends on the particle arrangement through the heat transfer and reaction heat. Accordingly, in the case of the mixed charge of the high reactivity nut coke in the ore layer, the design of the packed bed structure is important.
  • Feasibility of BF Hearth Protection Using Spinel Formation by Slag Composition Control

    pp. 1779-1785

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    DOI:10.2355/isijinternational.53.1779

    The formation of titanium carbonitride has been used as a conventional method to protect the refractory wear in the hearth. Because titanium carbonitride is formed only in the molten iron, the area that can form a protective layer in the hearth is limited. There is another possibility to protect the refractory wear by introducing the compounds with high melting point in the slags. If the compounds with high melting point are simultaneously formed in the molten iron and slag by adding TiO2, it might be more effective to form the protective layer and to prevent the refractory wear of hearth. However, the change of slag compositions and the formation of slag compounds can affect the slag viscosity and critical temperature, which might cause serious problems with blast furnace operation.
    In this study, to find the slag compositions for the effective compounds formation with maintaining the slag fluidity, the viscosity measurements, in-situ observation of compound formation by a confocal laser scanning microscopy and thermodynamical evaluation by FactSage has been carried out. Based on these results, the suitable slag compositions were suggested to form a protective layer in the hearth.
  • Development of High Efficiency Dephosphorization System in Decarburization Converter Utilizing FetO Dynamic Control

    pp. 1786-1793

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    DOI:10.2355/isijinternational.53.1786

    Laboratory experiments were carried out with the aim of adapting a (FetO) dynamic control technique, in which (FetO) is estimated by calculating the oxygen balance during blowing, to the hot metal decarburization process. The rephosphorization condition in the higher decarburization rate period was then clarified based on those experiments. Next, (FetO) control experiments were carried out in a commercial-scale plant converter. (FetO) generation was promoted by increasing the oxygen flow rate and raising the lance height in the early stage of blowing, and the amount of dephosphorization during blowing was increased. Finally, a dephosphorization model was constructed by combining the coupled reaction model and the (FetO) estimation model. This model suggested an increase of the amount of dephosphorization during blowing, and the effect was confirmed by an experiment with a commercial 240 ton converter.
  • Numerical Optimization of Nozzle Ports to Improve the Fluidynamics by Controlling Backflow in a Continuous Casting Slab Mold

    pp. 1794-1802

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    DOI:10.2355/isijinternational.53.1794

    In order to improve the fluid flow patterns inside the mold, a better understanding of the backflow phenomenon and its controlling parameters is necessary; then a mathematical simulation of the fluidynamics in the mold and the submerge entry nozzle (SEN) are carried out considering two typical nozzle designs and different modifications applied to the outlet ports. The numerical model considers isothermal three dimensional continuity and the Navier-Stokes equations in Cartesian co-ordinates, which are solved together with the k-ε standard turbulence and the Volume of Fluid (VOF) models through the volume finite method. The results show that the backflow phenomenon emerges from an inadequate SEN port design, when a boundary layer separation is generated before the steel is delivered to the mold. This separation occurs at the upper internal side of the port inducing a low pressure zone with high levels of kinetic energy dissipation, producing the backflow phenomenon. From the analysis, it is concluded that the implementation of a radius at the internal upper side of the port avoids the separation of the boundary layer, eliminating the backflow phenomenon which allows the use of the complete effective exit area of the port; this is reflected in a velocity decrease of the jets and consequently a velocity decrement of the bulk flow. Furthermore, the size of the radius controls the penetration angle of the jets, the impact point position and the meniscus deformation; which avoids the need of the inclination angle of the port.
  • Castability and Microstructural Development of Iron-based Alloys under Conditions Pertinent to Strip Casting – Specialty Fe–Cr–Al Alloys

    pp. 1803-1811

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    DOI:10.2355/isijinternational.53.1803

    A strip casting simulation of the iron-based specialty alloy known as Fecral (or Kanthal) has been carried out. The alloys tested were found to be easily castable and show good surface quality. Increasing the melt superheat increased the nucleation density and heat flux, leading to a refined ferrite grain size. Although changing the gas atmosphere during casting was observed to modify the measured heat flux, this did not correlate to any change in the nucleation density. The cast strips were able to be rolled without cracking, and showed mechanical properties similar to those found in comparable alloys after conventional thermo-mechanical processing.
  • Analysis of Crack Susceptibility of Regular Carbon Steel Slabs Using Volume-Based Shrinkage Index

    pp. 1812-1817

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    DOI:10.2355/isijinternational.53.1812

    The degree of peritectic solidification is a strong indicator of the cracking tendency of steel during continuous casting. To predict the crack susceptibility of regular carbon steel slabs, the characteristic index of solidification shrinkage (RV), which is determined by the volume shrinkage of the peritectic solidification and the remaining liquid phase after the peritectic solidification, is proposed as a means of evaluating the cracking tendency. In this study, RV was calculated for different steel grades under equilibrium condition. Then the segregation of the elements and the zone of the peritectic solidification under non–equilibrium condition were discussed with respect to the cooling rate. The results show that the calculated RV was in good agreement with experimental observations made on steel slabs, based on the zone of peritectic solidification under non–equilibrium condition. RV can therefore be used to predict the crack susceptibility of regular carbon steel slabs.
  • Thermo-mechanical Behavior of Peritectic Steel Solidifying in Slab Continuous Casting Mold and A New Mold Taper Design

    pp. 1818-1827

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    DOI:10.2355/isijinternational.53.1818

    Based on the descriptions of the thermal and mechanical behaviors of one peritectic steel solidifying in slab continuous casting mold, including shell shrinkage and deformation, air gap formation and mold flux film distribution in shell/mold gap, and shell temperature profile under the conventional mold taper by a two dimensional transient thermo-mechanical coupled finite element model, a new slab mold taper with non-linear slope narrow face and wedge-shape structures both for the wide and narrow faces corners was presented. The thermo-mechanical behaviors of solidifying shell and the applied effectiveness of improving shell subsurface cracks and reducing the wear of mold copper plate with the new mold taper were discussed. The results show that the mold walls of both wide and narrow faces match the shell shrinkage well under the new mold taper, and both the thicknesses and the distributions of air gap and mold flux film in the gap around shell corner and off-corners are greatly reduced. The shell grows uniformly in the mold. Moreover, the subsurface cracks both in the off-corners of slab wide and narrow faces, as well as the wear of the mold copper plate are also reduced significantly. The working life of the mold is greatly prolonged.
  • Direct Determination of Standard Gibbs Energies of the Formation of 4CaO·P2O5 and 3CaO·P2O5 by Transpiration Method

    pp. 1828-1835

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    DOI:10.2355/isijinternational.53.1828

    The standard Gibbs energy changes of the following reactions have been measured by using transpiration method;
    [ This part of text is omitted ]
    [ This part of text is omitted ]
    The standard Gibbs energies of the formation of 4CaO·P2O5 (ΔG°f,(4CaO·P2O5)) and 3CaO·P2O5 (ΔG°f,(3CaO·P2O5)) have been derived as follows;
    [ This part of text is omitted ]
    [ This part of text is omitted ]
    The reasons for discrepancies from reported values were discussed from the view point of whether the activity of phosphorus is measured directly or not.
  • A New Control Volume-based 2D Method for Calculating the Temperature Distribution of Rod during Multi-pass Hot Rolling

    pp. 1836-1840

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    DOI:10.2355/isijinternational.53.1836

    A simplified numerical model which can evaluate the 2D temperature distribution of a cross-section in multi-pass hot rod rolling process has been established. The grid of cross-section of workpiece under rolling was remeshed based on the energy rate balance of corresponding control volume. This method gives a quick way for the solution of heat-transfer during hot forming process, and can be applied to the on-line calculation. The validity of this method has been examined by FEM simulation and industrial measurement. The cross-sectional areas (elongations) and temperatures of workpiece calculated by the new method were in agreement with those obtained by the comparison methods.
  • Machinability Improvement and Its Mechanism in SUS304 Austenitic Stainless Steel by Precipitated Hexagonal Boron Nitride

    pp. 1841-1849

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    DOI:10.2355/isijinternational.53.1841

    To improve the machinability of SUS304 (Type 304) austenitic stainless steels, specimens were prepared containing 0.016 mass% boron and 0.2 mass% nitrogen, and hexagonal boron nitride (h-BN) particles with a diameter of 1 to 5 μm were precipitated. Precipitation of h-BN reduced the cutting force and tool wear during lathe turning with a cemented carbide tool insert, especially at cutting speeds of 40 m/min and higher. The reduction in cutting force appeared attributable to internal lubrication by h-BN in the chip shear region and the deformation flow layer, as well as to lubrication between the chip and carbide tool. Improved chip disposability and tool wear suppression were also achieved by h-BN precipitation. SUS304 steel with precipitated h-BN was found to exhibit good machinability in drilling and sawing operations with high-speed steel tools.
  • Experiments on and Finite Element Analyses of the Tilting of Fine Steel Wire in Roller Die Drawing

    pp. 1850-1857

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    DOI:10.2355/isijinternational.53.1850

    Roller die drawing is required for manufacturing low-formability materials such as high-carbon steels into fine wires with a diameter of 500 μm or less because of its characteristic lower friction than conventional die drawing. However, tilting, which is the inclination of the wire under the roll bite, often occurs in fine wires, which degrades their dimensional accuracy. Excessive tilting may generate wrinkling and overfill of the wire; thus, the design of the drawing setup of roller dies for reducing tilting is important from an industrial viewpoint. With the aim of designing a new setup for roller die drawing that can eliminate tilting; we carried out systematic experimental and analytical investigations. We first experimentally focused on the distance between adjacent rollers, and then theoretically focused on the area reduction ratio and roll-to-wire diameter ratio using the finite element method (FEM), taking the twisting moment as a representative parameter to evaluate the effect of different manufacturing conditions. It was found experimentally that there is a maximum threshold distance between adjacent rollers for preventing tilting. To draw a 200-μm-diameter wire without tilting, the roller distance should be set at no more than 8 mm, which leads to a more compact setup than the conventional one. Theoretical analysis revealed that a smaller area reduction ratio and a smaller roll-to-wire diameter ratio are required to reduce the tilting of the wire in roller die drawing.
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  • Electrodeposition Behavior of Zn–Co Alloys from an Alkaline Zincate Solution Containing Triethanolamine

    pp. 1858-1863

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    DOI:10.2355/isijinternational.53.1858

    Electrodeposition behavior of Zn–Co alloys was investigated at current densities of 2–500 A·m−2 and a charge of 5 × 104 C·m−2 at 308 K in an unagitated zincate solution containing triethanolamine, which forms a stable complex with Co2+ ions. At current densities lower than 5 A·m−2, the Zn–Co alloys exhibited normal co-deposition behavior, with the electrochemically more noble Co being preferentially deposited. By contrast, at current densities higher than 6 A·m−2, they exhibited anomalous co-deposition behavior, with the electrochemically less noble Zn being preferentially deposited. The current efficiency for Zn–Co alloy deposition was low (about 20%) in the normal co-deposition region, while it was 95% in the anomalous co-deposition region. Also, in the anomalous co-deposition region, the partial polarization curves for Co deposition and H2 evolution were significantly shifted to the less noble direction by the coexistence of Zn2+ ions, suggesting the formation of an inhibitor species that results from the presence of Zn2+ ions in the cathode layer. On the other hand, in the normal co-deposition region, the underpotential deposition of Zn apparently occured simultaneously with Co deposition. Zn–Co alloys are composed of stable intermetallic compounds CoZn13 and Co5Zn21; therefore, the activity coefficient of Zn in the deposits appears to decrease remarkably.
  • Electrodeposition Behavior of Zn–Ni Alloys from an Alkaline Zincate Solution Containing Ethylenediamine

    pp. 1864-1870

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    DOI:10.2355/isijinternational.53.1864

    Electrodeposition behavior of Zn–Ni alloys was investigated at current densities of 5–500 A·m–2 and a charge of 5 × 104 C·m–2 at 308 K in an unagitated zincate solution containing ethylenediamine (EDA), which forms a stable complex with Ni2+ ions. In the case of the TEA solution, the Zn–Ni alloy exhibited normal codeposition at low current densities, wherein electrochemically more noble Ni deposited preferentially, while it exhibited anomalous codeposition at high current densities, wherein less noble Zn deposited preferentially. In the EDA solution, the alloy exhibited anomalous codeposition at high current densities; on the other hand, even at low current densities, the Ni content in the deposit was almost identical with the composition reference line, showing a behavior similar to anomalous codeposition. In the EDA solution, Ni deposition and H2 evolution were significantly suppressed over a larger region of current densities, showing the formation of an inhibitor for deposition, which results from Zn2+ ions in the cathode layer. The dependence of the current efficiency for alloy deposition on the current density was smaller in the EDA solution than in that containing TEA. In the TEA solution, the underpotential deposition of Zn apparently occurred with Ni, while in the EDA solution, the underpotential deposition of Zn never occurred, because Ni deposition was suppressed by the coexistence of Zn2+ ions even at low current densities. The throwing power of Zn–Ni alloys in the EDA solution was better than that in the TEA solution.
  • Effect of Intercritical Heat Treatment on the Microstructure and Mechanical Properties of Medium Mn Steels

    pp. 1871-1880

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    DOI:10.2355/isijinternational.53.1871

    In the present work, the effects of intercritical annealing parameters on the microstructure and cold rollability (deformation rate and ratio) of “3rd Generation Advanced High Strength Steels (AHSS)” were studied. Hence, this paper discusses the formation of microstructures with different volume fractions of ferrite, martensite, bainite and retained austenite (RA). Two novel microstructures have been created, based on two levels of manganese (Mn): (i) ferrite plus martensite nucleated in austenite microstructure (FMNA structures), using Mn levels of 5 to 7 wt% and (ii) ferrite plus retained austenite duplex structure (FADP steels) for a Mn level of 10 wt%. In general, the ductility is a function of the amount of retained austenite and the strength is highly dependent on the martensite level.
  • Effects of Temperature and Strain Rate on TRIP Effect in SUS301L Metastable Austenitic Stainless Steel

    pp. 1881-1887

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    DOI:10.2355/isijinternational.53.1881

    Effects of temperature and strain rate on tensile properties in metastable austenitic stainless steel SUS301L were studied in order to clarify the conditions of stress-induced martensitic transformation behavior for the maximum uniform elongation through the TRIP effect. The experimental results of the previously studied SUS304 steel were used to compare the conditions of metastable austenitic steels with different austenite stability. In the static tensile tests for the SUS301L steel at temperatures between 123 K and 373 K, the tensile strength increased with decreasing temperature, and uniform elongation reached a maximum at 323 K. The volume fraction of stress-induced martensite (Vα) at the same true strain increased with a decrease in temperature. For the strain-rate dependence on transformation kinetics, Vα decreased at strain rates higher than about 10–2 s–1 due to the temperature rise caused by adiabatic deformation. The equation for stress-induced transformation behavior proposed by Matsumura et al. was modified to consider the saturation value of stress-induced martensite, and the modified equation could describe the transformation kinetics precisely. The conditions of stress-induced transformation for the maximum uniform elongation through the TRIP effect were coincident between the SUS301L and the SUS304 with different austenite stability: the volume fraction of martensite at a true strain of 0.3 is approximately 5% and the maximum transformation rate is almost 2 at a higher true strain near uniform elongation.
  • Determination Method for Maximum Calcium Releasing Potential from Steel Slags, Marine Sands Alternatives in Seawater

    pp. 1888-1893

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    DOI:10.2355/isijinternational.53.1888

    Sea grass beds and tidal flats are facing imminent dangers of extinction. Steel slags are one of the promising alternative materials for marine sands to restore sea grass beds and tidal flats. On the other hand, significant pH increase and solidification attributed to dissolving calcium released from the slags are sometimes negative impact on ecosystems. To quantify the dissolved calcium, Japan Cement Association Standard method is conventionally used. However, our study leveled the method underestimate the dissolved calcium from the steel slags. The purpose of this study is to optimize the determination method for maximum calcium releasing potential from steel slags. Powdered sample (0.1 g) was stirred in 40 mL of 99.5% ethyleneglycol-100 mM tris buffer solution for 6 h at 80±5°C. Thereafter, the solution filter through 0.45 μm filter and the dissolved calcium was determined by ICP-AES. The optimized condition proposed in this study recovered the dissolved calcium from the slag in seawater perfectly.
  • Decrease of Sulfide in Enclosed Coastal Sea by Using Steelmaking Slag

    pp. 1894-1901

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    DOI:10.2355/isijinternational.53.1894

    Currently in Japan, 15 million tons of steelmaking slag as a by-product of the steelmaking process is produced annually. More than 60% of the steelmaking slag is used in civil construction. steelmaking slag has special properties which are presently under-exploited. Therefore, research into the greater utilization of the special characteristics of steelmaking slag in coastal environments has been undertaken over the last 20 years. It is known that steelmaking slag can reduce hydrogen sulfide in seawater. Hydrogen sulfide is highly toxic and fatal to benthic organisms. It also depletes oxygen and generates blue tide.
    The purpose of this study is to evaluate and demonstrate the effects of removal of hydrogen sulfide in seawater by steelmaking slag. Both the laboratory and the field experiments showed that steelmaking slag removed the hydrogen sulfide from seawater and reduced the concentration of hydrogen sulfide in sediment. The field experiments also indicated that steelmaking slag changed the anaerobic condition of sediment into an aerobic condition. The results imply that effective utilization of steelmaking slag in coastal area restoration can significantly improve the surrounding marine environment.
  • Predictive Model for Austenite Grain Growth during Reheating of Alloy Steels

    pp. 1902-1904

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    DOI:10.2355/isijinternational.53.1902

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