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

ISIJ International Vol. 50 (2010), No. 6

  • Production and Technology of Iron and Steel in Japan during 2009

    pp. 777-796

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    DOI:10.2355/isijinternational.50.777

  • Interfacial Phenomena in Metal–Slag–Gas System during AOD Process

    pp. 797-803

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    DOI:10.2355/isijinternational.50.797

    Significance of interfacial phenomena and properties such as surface tension are essential in iron and steelmaking processes due to chemical reactions occurring on the interfaces including elements transfer through the phase boundaries. In this study, the influences of surface tensions of slag and metal and interfacial tension between slag and metal on the behavior of metal–slag–gas system were analysed based on the energy bound to system surfaces. Effects of reactions between slag and steel on the behavior of metal–slag–gas system during AOD process were evaluated by two cases: evaluation of top slag–steel melt system and single bubble rising in the metal bath.
    Simulations for metal–top slag system show that there are no possibilities to form metal film around the gas bubbles when they penetrate through metal–slag interface. Behavior of system is also independent of intensity of reactions between slag and steel. According to the calculations during intensive metal–slag reactions metal droplets are disintegrated more easily into top slag layer. If there are no metal–slag reactions metal droplets are attached into the gas bubbles.
    Calculations prove that, when reactive oxygen gas bubble forming oxides is injected into steel bath, slag film can be formed around the gas bubble if the intensity of reactions between the slag and the metal is high. During effective oxidation reactions at the vicinity of nozzles formed micro slag is attached with the rising gas bubble.
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  • High-temperature Interactions of Alumina–Carbon Refractories with Molten Iron

    pp. 804-812

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    DOI:10.2355/isijinternational.50.804

    The interfacial behaviour of alumina/carbon refractories with liquid iron was investigated at 1550°C, with emphasis on the chemical interactions occurring both in the interfacial region as well as in the bulk of the refractory. The sessile drop technique was used to determine the interfacial wetting behaviour and the phase transformations during the chemical reactions were determined using SEM and EDS. Alumina–carbon refractories were prepared using two types of carbonaceous materials–synthetic graphite and natural graphite. From the experimental results, it was clearly observed that molten iron had penetrated to varying extents into all refractory substrates. The highest penetration was observed for alumina–carbon refractory substrates containing 10% synthetic graphite, while all alumina–natural graphite substrates showed much lower levels of metal penetration. Contact angles for synthetic graphite and natural graphite containing refractories showed an initial drop in the first 5 min of the experiment before increasing and stabilising at different values depending on the composition of the refractories. The initial drop in the contact angles was in direct correspondence with increasing carbon pickup values for these samples. Natural graphite samples generally showed lower carbon pickup as compared to synthetic graphite samples of similar carbon content. The differences in metal penetration and interfacial wetting behaviour were found to depend on the carbon pickup and the ash content of the refractory substrates, with the ash helping in the formation of an interfacial layer which limited reactions with the metal, and in filling the pores within the refractory.
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  • Simulation of Effect of Pore Structure on Coke Strength Using 3-dimensional Discrete Element Method

    pp. 813-821

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    DOI:10.2355/isijinternational.50.813

    The compression and cleavage simulations of cylindrical coke sample using 3-dimensional Discrete Element Method are carried out to investigate failure phenomena of coke, and the results are discussed by comparing with experimental results.
    The following assumptions are applied to model coke. Coke matrix is an aggregation of primary particles which are connected by parallel bonds to be broken when the stress exceeds its corresponding bond strength. The voids between the primary particles are considered as pores and ‘large pore balls’ are inserted intentionally to investigate the effect of large pores on the coke strength by regulating their size and location.
    According to the results, porosity is the most dominant factor for coke strength when it is compared with the strength of coke matrix texture. When large pores are distributed regularly they strengthen the coke compared with the randomly arranged cases. In the cleavage test, critical strength of coke sample is proportional to the exponential of porosity and minimum coke matrix area fraction of crack propagated cross sections.
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  • Distribution of P2O5 between Solid Solution of 2CaO·SiO2–3CaO·P2O5 and Liquid Phase

    pp. 822-829

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    DOI:10.2355/isijinternational.50.822

    It is desirable to decrease the phosphorous content of steel and the amount of slag in steel refining. For satisfying this requirement recently, the importance of multiphase slag in steel refining has been given considerable attention. Normally, hot metal dephosphorization slag consists of the CaO–SiO2–FeO–P2O5 system, and the industrial operation is mainly carried out in the dicalcium silicate (C2S) saturated region. It is well known that C2S forms a solid solution with the main product of dephosphorization—tricalcium phosphate (C3P)—at the treatment temperature over a wide composition range, and a high distribution ratio of P2O5 between the solid solution and the liquid phase has been reported. In order to determine the ruling factors on the distribution ratio, the influences of MgO, MnO, and Al2O3 were investigated for various slag compositions in the case of FeO or Fe2O3 as the iron oxide. First, a mixture of a standard regent was heated to the melting temperature in order to produce homogenous liquid slag. Next, it was cooled down to a semisolid state: during cooling, the solid solution of C3P–C2S was precipitated under the equilibrium condition. For clarifying the influence of slag composition on the distribution ratio, the ruling factors on the activity coefficient of P2O5 in the solid solution and liquid slag phase were evaluated. It is the contention of this research that the activity coefficient of P2O5 in the solid solution was largely influenced by P2O5 and the total solved oxide content of the solid solution. (log γP2O5SS)cal was obtained empirically in order to represent the activity coefficient in the solid solution. On the other hand, the activity coefficient of P2O5 in the liquid phase was strongly influenced by the CaO content of the liquid phase. On the basic of these correlations, it was shown that the CaO content of the liquid phase and (log γP2O5SS)cal are the ruling factors on distribution ratio.
  • Shell Thinning Phenomena Affected by Heat Transfer, Nozzle Design and Flux Chemistry in Billets Moulds

    pp. 830-838

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    DOI:10.2355/isijinternational.50.830

    Shell thinning affected by nozzle design, flux chemistry, heat transfer and steel flow was simulated through a mathematical model. Two nozzles were studied, the first, S60 with outer and inner diameters of 60 mm and 36 mm and the second, S73, with outer and inner diameters of 73 mm and 36 mm, respectively. Casting conditions include a casting speed of 1.3 m/min, use of a basic flux and a superheat of 36 K. Simulations included hypothetical isothermal casting conditions compared with casting conditions under thermal gradients. Simulation results indicated that the buoyancy forces, generated by thermal fields, exert a braking effect on the discharging jet whose magnitude was approximately 1/4 of the inertial forces. Shell growth along the curved mould walls suffers considerably thinning effects through the transport of sensible heat by convective mechanisms. Both nozzles induce shell thinning although, predictions of this mathematical model, using nozzle S73, indicate severe shell thinning effects in a region located in the inner radius side, down the second half of the mould length. This final shell thickness is very small making possible the existence of a strand breakout. Steel solidification along the flat mould walls leads to thick and uniform shells using either of these nozzles. The present numerical results indicate that in the field of flux design steel chemistry must be taken into account together with nozzle design.
  • Effect of Thermal Cycle and Nitrogen Content on the Hot Ductility of Boron-bearing Steel

    pp. 839-846

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    DOI:10.2355/isijinternational.50.839

    Hot ductility of Boron (B)-bearing steel has been examined in view of slab corner cracking problem. Addition of B to the low carbon steel reduced its hot ductility under a thermal cycle in which samples were cooled directly to the test temperature before straining. The change in hot ductility of B-bearing steel with deformation temperature showed one trough in the temperature range of 800–1000°C, which covered the lower temperature region of austenite single phase (region (I)), and near the austenite/ferrite transformation temperature (Ae3) (region (II)). An abrupt temperature decrease and reheating before straining heavily deteriorated the hot ductility of B-bearing steel in the region (I). In all steels, the strain concentration in the film-like ferrite primarily reduced hot ductility in region (II) regardless of the addition of B and the thermal cycles before straining. The ductility reduction of B-bearing steel is caused by the distribution and amount of BN precipitation, which is determined by the thermal cycles and the N content. Increase in the N content remarkably reduced hot ductility of B-bearing steel in region (I), where the behavior of BN precipitates controlled hot ductility. The results shows that the improvement of hot ductility in B-bearing steel can be attained by decreasing the N content and by avoiding an abrupt temperature decrease in the secondary cooling stage of the slab after solidification.
  • Solidification of Thin Wall Ductile Iron Castings with Hypereutectic Composition

    pp. 847-853

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    DOI:10.2355/isijinternational.50.847

    Numerical calculations are presented describing the solidification of a thin wall ductile iron castings with a hypereutectic composition. Numerical model was implemented in Matlab–Simulink environment. The model takes into account the presence of off-eutectic austenite as well as primary graphite. Experimental verification was made using casting with the shape of Archimedes spiral. Thermal analysis showed that there is high temperature drop of liquid metal due to intensive heat transfer between the flowing metal stream—the mould material. Thermal analysis along with microstructure observations were made and show reasonable agreement of numerical calculations with experimental measurements.
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  • A Web Tension Control Strategy for Multi-span Web Transport Systems in Annealing Furnace

    pp. 854-863

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    DOI:10.2355/isijinternational.50.854

    This paper presents a web tension control strategy for multi-span web transport in a continuous annealing process (CAP) used in steel manufacture. In the CAP, the temperature of the steel web is varied over a wide range, and this generates a thermal strain in the web. In addition, in order to save workspace, vertical type web transport systems are usually used, and the weight of the web causes a gravity strain in the web. These strains in the web induce the variation of the web tension. To control the web tension in the CAP, a feed-forward tension control scheme is suggested, which is based on a mathematical model considering the additional strains due to thermal and gravity effects. The performance of the proposed feed-forward tension control scheme is experimentally evaluated in an actual CAP. In addition, to respond to the variations of many system parameters, a feedback tension control scheme based on the tension observer is proposed. The performance of the feedback tension control system is evaluated by computer simulation.
  • Observation of Atomic Emission Image from Spark Discharge Plasma by Using Two-dimensional Spectrograph

    pp. 864-867

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    DOI:10.2355/isijinternational.50.864

    In order to obtain detailed information on the excitation process which takes place in a spark discharge (SD) plasma, a two dimensional image of atomic emission was observed by using an imaging spectrograph equipped with a charge-couple device (CCD) detector. The emission image of copper emission (Cu I 324.75 nm) emitted from a SD plasma region induced in argon at a low pressure has been successfully observed. It indicates that the copper emission is the most intense at plasma zones being 1.5–2.0-mm apart from the sample surface and becomes weaker at larger distance from the central zone of the SD plasma region, and that the emission image changes with time; where the optimal condition of the emission image is obtained at a delay time of 40 μs. These results could be valuable information in order to have better understanding about the complicated spectrochemical phenomena occurring in the SD plasma.
  • Simplification of Hot Rolling Schedule in Ti-Microalloyed Steels with Optimised Ti/N Ratio

    pp. 868-874

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    DOI:10.2355/isijinternational.50.868

    Thermomechanical simulations have been carried out on two Ti-microalloyed steels and one reference steel without Ti. The pinning forces exerted by TiN particles in the Ti-steels have been determined and compared with the driving forces for austenite grain growth and static recrystallisation between hot rolling passes. The driving forces for recrystallisation were found to be approximately two orders of magnitude higher than the pinning forces, which explains why the austenite in these steels barely experiences hardening during rolling and why the accumulated stress prior to the austenite→ferrite transformation is insufficient to refine the ferritic grain. On the other hand, austenite grain size hardly varies during hot rolling, as the TiN precipitates exert a strong control from the reheating temperature to the last pass. A Ti/N ratio close to 2 is able to control austenite grain growth at high austenitisation temperatures. So, both aspects-high driving forces for static recrystallisation and control on austenite grain size-allow reducing the number of passes applied. In this case, ferrite grain refinement should be reached by austenite strengthening and accelerated cooling during the transformation to ferrite.
  • Comparison of the Dislocation Density in Martensitic Steels Evaluated by Some X-ray Diffraction Methods

    pp. 875-882

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    DOI:10.2355/isijinternational.50.875

    X-ray diffraction (XRD)-based modified Warren–Averbach (MWA) analysis, in comparison with the Williamson–Hall (WH) analysis, was applied to 0.3 mass% carbon martensitic steels, as-quenched and subsequently tempered at various temperatures, to give their dislocation densities. For the as-quenched martensite, the WH method gives a value of around 2.0×1016 m−2, which could be overestimated. Meanwhile, the MWA method gives a value of around 6.3×1015 m−2, which is below the possible upper limit of dislocation density, 1016 m−2. The MWA-derived value for the as-quenched steel seems to be 1.6–4.8 times higher than those expected from the precedent results derived by transmission electron microscope (TEM) observations. However, considering that the TEM-derived value gives the microscopically local average while the XRD-derived value gives the macroscopic average, such discrepancy between the TEM-derived value and MWA-derived value is tolerable. For the steels tempered at 723 K and 923 K, the MWA and WH methods give comparable values ranging in 1014 m−2, where the rearrangement of dislocation structure is observed by TEM. However, in these steels where the XRD peaks are narrower and the instrumental width of the present XRD system could be significant, care should be taken over the peak width correction.
  • Analytical Investigation on Ultimate Behaviors for Steel Heavy Clip-angle Connections Using FE Analysis

    pp. 883-892

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    DOI:10.2355/isijinternational.50.883

    This paper describes an analytical investigation on the strength, stiffness, and mechanical behavior of heavy clip-angle connections subjected to static loading. The work is based on the results of a large experimental investigation into the cyclic behavior of connection components incorporating with thick clip-angles. The results of these tests are described first, and then methodologies to generate the response of connection components, utilizing nonlinear finite element (FE) models with the advanced modeling methods such as the pretension force in the bolts and the interaction between two contact surfaces, are presented in this study. Numerical test results obtained from FE analyses are compared with experimental test results in an effort to verify that 3D FE models can simulate the overall and detailed behavior of a various type of clip-angle connections accurately. These FE models provide useful instrumentation, which is difficult to obtain during an experiment, such as the distribution of the plastic strain, prying forces induced by the initial bolt pretension, and friction forces on the interface between a clip-angle and a steel beam. These valuable results can support the basic knowledge for developing strength models consistent with the AISC-LRFD component method of the clip-angle design. They are also utilized to better understand the parametric effect of connection components and achieve a comprehensive study of their behavior.
  • High-strength Fe–20Mn–Al–C-based Alloys with Low Density

    pp. 893-899

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    DOI:10.2355/isijinternational.50.893

    Mechanical properties of Fe–20Mn–(10–14)Al–(0–1.8)C (mass%) quaternary and Fe–20Mn–(10–14)Al–(0.75–1.8)C–5Cr (mass%) quinary alloys were investigated by hardness, cold-workability and tensile tests at room temperature. The γ(fcc) alloys in both quaternary and quinary systems with a low density of less than 7.0 g/cm3 showed an excellent ductility and their hardness and tensile strength increased with increasing Al and C contents. The γ+α(bcc) duplex alloys also exhibited a high tensile strength by controlling the α volume fraction. TEM observation confirmed that high hardness and tensile strength of the alloys with high Al and C contents are caused by the precipitation of nano-size κ-carbide with perovskite structure during cooling from the annealing temperature. Fe–20Mn–11Al–1.8C–5Cr alloy with a density of 6.51 g/cm3 showed a high specific strength of more than 180 MPa·cm3/g with a good tensile elongation of 40%. The present Fe–20Mn–Al–C(–5Cr) alloys showed a higher specific strength than conventional steels.
  • Comparative Studies on Friction and Wear Performance between Glass-fiber Reinforced Polyamide 66 Composite and Ductile Irons on Ceramic Al2O3 Counterface in Sucker Rod Centralizer Application

    pp. 900-905

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    DOI:10.2355/isijinternational.50.900

    The tribological behaviors of three materials for sucker rod centralizer application including glass-fiber reinforced polyamide 66 composite, ductile iron and quenched ductile iron were investigated on the pin-on-disc type wear testing machine against ceramic Al2O3 under both dry sliding and oil field water lubricated conditions. Laser optical microscopy, scanning electron microscopy, Fourier transform infrared spectrometer, digital temperature measurement system and X-ray photoelectron spectroscope were used to investigate the microstructure, wear mechanism and chemical nature change of the studied materials. The results revealed that the coefficients of friction under oil field water lubricated condition were slightly lower than those under dry sliding condition for the studied materials, in which glass-fiber reinforced polyamide 66 composite exhibited the lowest coefficient of friction. The quenched ductile iron showed the lowest wear volume among the studied materials under both dry and lubricating sliding conditions. The wear loss of glass-fiber/polyamide 66 composite was much higher under lubricating condition than that under dry sliding condition, and much higher than those of as-cast and quenched ductile iron, which was attributed to the combination of thermal deformation, degradation and micro-ploughing.
  • Quality Control by Means of Ultrasonic in the Production of Ductile Iron

    pp. 906-912

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    DOI:10.2355/isijinternational.50.906

    The paper presents several concepts of physical substantiation for the rationale of building the relationships between mechanical properties and ultrasonic inspection indicators. Special emphasis is put on assessing the influence of graphite shape number SS and the number of graphite precipitations NA on the tensile strength and longitudinal ultrasound wave velocity of ductile iron manufactured under production conditions. Tests were conducted on wedge casts which were used as samples for tensile tests and a map of the structure and longitudinal ultrasound wave velocity was determined for the cast wedges. The tensile tests were conducted and values of graphite shape number, average number of graphite precipitations and longitudinal wave velocity were determined in the place where the sample was broken. Relations between the mechanical properties, graphite shape number, number of graphite precipitations and the velocity of longitudinal ultrasonic wave were determined.

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