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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 81 (1995), No. 6

  • Development of "In-situ" Observation System for Oxide Films Formed during Thermal Oxidation Using Raman Spectroscopy

    pp. 607-612

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    In-situ observation system for oxidation films using laser Raman spectroscopy was constructed and the growth processof oxide films during thermal oxidation of Fe-6.5mass%Si alloy at 1073K in O2, CO2 and CO-CO2 (PCO/PCO2=1) atmospheres was investigated. In-situ Raman spectra of the oxide films formed in these atmospheres could be_obtained using the system with an SN-filter and a chopper unit to reduce the effect of Rayleigh scattering and thermal radiation. In a CO, atmosphere strong Raman peaks of Fe3O4and α-Fe2O3 were observed even in the early stage of oxidation of the alloy, which suggested that the oxidation rate in the CO2 atmosphere was higher than that in the O2 or CO-CO2 atmosphere. Since the difference of oxidation behavior in these atmospheres was not detected by thermogravimetry, the usefulness of the system at high temperatures was confirmed.
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    3. Mathematical Modelling of Clearance between Wall of Coke Oven and Coke Cake Tetsu-to-Hagané Vol.81(1995), No.6
  • Estimation of Hydroxyl Capacity of Molten Slags by Cell Model

    pp. 613-618

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    A statistical thermodynamic model, cell model, has been attempted to represent the hydroxyl capacities of some moltensilicates and molten aluminates. The slag systems discussed were CaO-SiO2, CaO-Al2O3 binaries and CaO-SiO2-MgO, CaO-Al2O3-MgO and CaO-SiO2-Al2O3 ternaries. The cell model is based on the description of the liquid in terms of cells composed of an oxygen anion surrounded by two cations (i, j). In addition to binary parameters, Wij and Eij a new parameter, W'Hi was introduced into the cell model for representing the hydroxyl capacity. Here, W'Hi is free energy of formation of dilute H-O-i cell. The hydroxyl capacities calculated by the model agreed with the experimental data over the wide range of slag composition and temperature. A good correlation between WHiand free energy of formation of hydroxide was confirmed. Therefore, the cell model with the new parameter W'Hiis considered to be applicable to predict the hydroxyl capacities of multicomponent slags.
  • Thermo-chemical Activities of Liquid Fe-Mn-C Alloy

    pp. 619-624

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    High carbon ferro-manganese alloys are used to produce high manganese steels for non-magnetic materials. During the decarburization of the high manganese hot metal, oxidation loss of manganese occurs concurrently. To minimize the oxidation loss of manganese and to establish an optimum dacarburization process, it is important to know the thermodynamic properties of the liquid Fe-Mn-C alloys with high Mn concentration and wide concentration range of carbon.
    In the present study, measurements were carried out of the activity of Mn in liquid Fe-C-Mn alloys. Distribution equilibrium of Mn between Fe-Mn-C alloys of different C concentration via a liquid Ag-Mn alloy bath was employed to determine the activity of Mn.
    The experimental concentration range of Mn was from 0 to 45 mol% and that of C was 0 to saturation and the experimental temperatures were 1736, 1773 and 1823K. The activity coefficient on the base of lattice ratio of manganese was found to be expressed properly with up to the second order terms by the use of lattice fraction as the concentration of solute elements. The interaction of Mn and C of liquid Fe-C-Mn ternary alloys were given as the functions of temperature and composition of the alloy.
    The activity coefficient of C was also derived from the obtained parameters.
  • Mathematical Modelling of Clearance between Wall of Coke Oven and Coke Cake

    pp. 625-630

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    The mathematical model was developed for estimating the clearance between the wall of coke oven and the coke cake.The prediction model is based on the balance between the contraction force and the coking pressure. The clearance begins to generate when the contraction force exceeds the coking pressure in this model. Contraction force is calculated in consideration of the visco-elastic behaviour of the thermal shrinkage of the coke. Coking pressure is calculated considering the generation and the dispersion of the gas in the melting layer. The relaxation time of coke used in this model was obtained by load test applied dilatometer. The clearance was measured by laser sensor and internal gas pressure was measured at 1/4 width away from wall, in 40kg test oven. The clearance calculated during the coking process were in good agreement with the experimental results, which supports the validity of the mathematical model. The model enables us to quantitatively understand the effects of coal properties, such as mean reflectance and maximum fluidity on the clearance formation.
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    Readers Who Read This Article Also Read

    1. Development of "In-situ" Observation System for Oxide Films Formed during Thermal Oxidation Using Raman Spectroscopy Tetsu-to-Hagané Vol.81(1995), No.6
    2. Sintering Process Usiug Pisolite Lumpy Ore as Hearth Layer Tetsu-to-Hagané Vol.80(1994), No.4
    3. Rist Operating Diagram(I) Tetsu-to-Hagané Vol.79(1993), No.9
  • Solidification of Middle Carbon Steel on the Smooth or Rough Mold Surface

    pp. 631-636

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    In order to investigate the nucleation phenomena on the surface of mold wall, two types of surface condition of chill blocks have been immersed in the molten steel. When the mold A, of which surface is flat, was immersed, irregular shell was obtained and very-fine-solidified structure which locates in the thicker region was observed on the chill block side of the shell. On the other hand, when the mold B, of which surface is rough, was immersed, uniform shell was obtained and regular columnar dendritic structure was observed.
    The shape of very-fine-solidified structure (mold A) is hemisphere. The degree of recalescense for nucleation close to the flat chill block measured by fine thermocouple was 20K, which is larger than that close to the rough chill block.
    These results may come from the difference of nucleation phenomena on the mold surface. The details are followings.:
    When the flat chill block is immersed, nucleation on the surface is difficult to occur, therefore undercooling becomes large. In the same time the undercooled region becomes large. The dendrites, growing rapidly in the largely undercooled, are very fine and they correspond to the thicker part of shell. Finally shell with irregular thickness is obtained. When the rough chill block is immersed, nucleation is easy to perform, therefore undercooling for nucleation is small and uniform columnar dendritic structure is observed.
  • Relation between Surface Quality of Cast Strips and Meniscus Profile of Molten Pool in the Twin Roll Strip Casting Process

    pp. 637-642

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    Experiments of laboratory scale twin roll casting to observe strip surface quality and to detect contact point between molten metal and roll by immersing a refractory bar into the molten metal pool have been done using stainless and carbon steels and copper alloy to elucidate the relation between surface quality and meniscus behavior of molten metal. Furthermore, dynamic meniscus profile near the roll surface and critical casting speed controlling surface wrinkles have been theoretically analyzed.
    With increasing casting speed, the depth of surface wrinkles became shallow and the flat surface was obtained. The observed critical speed for the wrinkle-free surface was roughly 0.45 to 0.6m/s for the cast metals. By the immersion of refractory bar over a depth, the solidification of columnar dendrite zone was delayed and the surface wrinkle was resultantly taken place. With increasing casting speed, the depth of bar to result in surface wrinkles increases and the contact point between molten metal and roll moves downward.
    It has been theoretically found that the descent of meniscus increases with increasing casting speed and surface tension of molten metal and with decreasing the density. The surface wrinkle does not appear when the descent of meniscus is deeper than a critical value, because vibration of the molten pool surface due to the teeming flow becomes less influential for the contact point. A theoretical equation of the critical speed for preventing surface wrinkles has been presented to show that it increases with increasing the critical descent of meniscus and the density and with decreasing the surface tension.
  • Gas Wiping Mechanism in Hot-Dip Coating Process

    pp. 643-648

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    The liquid film flow on a strip steadily moving upward from a coating liquid bath in the gas wiping process for continuous hot-dip coating was analytically investigated assuming that the flow was time-independent and laminar and the surface tension was negligible. The coating thickness profile of the liquid film can be estimated by solving the equation of motion under the boundary conditions that both the impinging pressure and the shear stress of the gas wiping jet act on the liquid film surface. The analytical results of the coating thickness profiles agree well with the experimental results measured by the needle electrode method using glycerine-water solution. The analytical results were also compared with data obtained in a commercial hot-dip galvanizing line. It is confirmed that the effects of the line speed, the nozzle pressure, the nozzle-to-strip distance and the nozzle slit gap on the zinc coating weight can be explained well by the analysis and that the coating weight can be estimated within ±20% accuracy.
  • Prediction of Volume Fraction and Grain Size of Ferrite under Intercritical Rolling of Low Carbon Steels

    pp. 649-654

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    Static recovery and recrystallization behavior of α grains of low carbon steels have been studied by means of hot working simulator. Static recovery rate increases as carbon content increases up to 0.02mass% and is nearly constant above 0.02mass%. The critical strain for recrystallization, εm, decreases with decreasing initial grain size and strain rate and with increasing deformation temperature. Recrystallized grains are developed within an interval of 50 ms after straining over εm. Recrystallized α grain sizes decrease with decreasing initial grain size and deformation temperature, and with increasing strain. Recrystallized fraction increases with decreasing initial grain size and with increasing strain and deformation temperature. 2-step hot working tests at various temperatures above and below Ae3 have been carried out to examine the strain induced transformation from hot worked austenite to ferrite.
    On the basis of these results, a prediction model of α volume fraction and grain size is developed and its availability in the case of intercritical rolling was certified.
  • Influence of Cr and Al on the Properties of Nitrided Cases of Steels

    pp. 655-660

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    Influence of Al and Cr on the properties of nitrided cases was studied for JIS-SACM645, SCM440 and SKD61 steels under as-nitrided (793K-216ks) and reheated (773 to 973K-3.6ks) conditions, using hardness measurement and X-ray diffraction analysis.
    Hardness and residual stress distribusion in the nitrided case did not change under as-nitrided condition and reheated condioion at 873K for 3.6ks after nitriding for any of the three steels. SCM440 and SKD61 steels, containing Cr, showed good correlation between hardness of nitrided case and lattice strain induced by nitrogen atoms, while SACM645 steel, containing Al, showed no correlation. The hardening mechanism of nitrided case therefore differ between Cr containing steel and Al containing steel.
  • Effect of Testing Atmosphere on Low Cycle Fatigue of Hot Work Tool Steel at Elevated Temperature

    pp. 661-666

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    Effects of atmosphere and strain amplitude on low cycle fatigue behavior of SKD6 hot work tool steel were investigated. The fatigue life in vacuum was twice as long as that in air. It became clear from the results obtained from the experiment conducted in vacuum that slip bands on the specimen surface were formed during fatigue and grew up with increasing number of cycles. The initial fatigue cracks were generated at the intersections of slip bands and were vertical to loading direction. The fatigue cracks mainly initiated at internal inclusions when tested in vacuum, whereas superficial cracks were observed on the same fracture surface when applied higher strain amplitude. In contrast, nucleation sites of fatigue crack when tested in air were specimen surface irrespective of the magnitude of strain amplitude. The improvement of low cycle fatigue properties in vacuum was mainly due to the decreasing of growth rate of superficial and internal cracks to the critical crack length.
  • Effect of Stress on Morphology of γ'-phase and Creep Strength Properties of Inconel 713C

    pp. 667-672

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    Creep rupture strength and morphology of γ' phase of. Inconel 713C. especially the effects of both long-term creep deformation and applied stress on γ-γ' microstructure, have been investigated mainly at 1000°C. The scatter band of creep rupture strength has increased with decrease in stress. Rafted γ' structure has not been formed during creep deformation at 47MPa, but formed under the stresses higher than about 100MPa. Morphology of γ' phase was assessed by both the distribution of γ' phase with respect to angle with stress axis and the aspect ratio of γ'-phase. It has been concluded that higher stresses are needed for polycrystalline Ni based superalloy to form a rafted γ' structure and the stress dependence of γ-γ' microstructure developed should be considered for a long-term service at elevated temperature.
  • Plastic Stability of Retained Austenite in the Cold-rolled TRIP Sheet Steel

    pp. 673-678

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    Mechanical properties of cold-rolled and continuously annealed TRIP steel with 0.14%C-1.9%Si-1.7%Mn have been discussed especially from the aspect of the plastic stability of retained austenite which was varied by changing austemper time at 400°C. The results obtained are as follows ; The plastic stability of retained austenite and the strength-ductility balance at room temperature are improved with the increase in C content in retained austenite after optimizing the austemper time in the continuous annealing process. Martensitic tranformation is considered to occur from the plastically unstable retained austenite with low C content. The kinetics model for deformation-induced martensitic transformation explains the experimentally obtained change in volume% of retained austenite with plastic strain in terms of the C content in retained austenite.
  • The Best Suitability of Damping Properties on Vibration Damping Steel Sheet Having Three Layered Structure

    pp. 679-684

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    The characteristics of vibration damping steel sheet, which has three layered structure of steel/viscoelastic resin/steel, were examined. They were affected theoretically by material conditions, such as viscoelastic properties of resin and configuration of each layer, and also by mechanical vibration conditions, such as vibration mode and supporting condition. The influences of material conditions on the loss factors were examined experimentally under several constant conditions of mechanical vibration conditions. It is concluded from the present results that loss factors of vibration damping steel sheet are determined by not only a loss factor of resin itself but also rigidity and thickness of resin as well as steel sheet. These results give a guide for the best suitability for a loss factor of vibration damping steel sheet.
  • Damping Behavior of Pre-strained High Mn Steels

    pp. 685-689

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    Effects of prestrain on internal friction (δ) at room temperature were investigated using a 28Mn-6Si-5Cr steel, in comparison with a 16Mn-5Ni steel which had been reported as a new type of damping material. A transversal vibration method with a frequency of 500 Hz and a strain amplitude of about 2×10-5 was employed. Shape memory effect of the same 28Mn-6Si-5Cr steel was also examined to estimate the variation of deformation mode (γ→ε transformation or slip) with prestrain.
    With an increase in prestrain, δ changes almost parallel with the change in amount of ε phase in both steels. In the 28Mn-6Si-5Cr steel, moreover, nearly complete shape memory effect is observed up to 1% prestrain, while the amount of shape recovery strain exhibits a maximum at the prestrain of 5 or 6%. Considering the well known effects of ε phase on shape memory in high Mn-Si steels, the above results show that the increase in δ with increasing amount of prestrain up to 5 or 6% is attributed mainly to the ε phase which has been induced by prestraining. This suggests that the existence of ε phase is a major factor controlling the internal friction in high Mn steels.
  • The Effects of Vacuum Heat Treatments on Bonding Strength of Anodically Oxidized Titanium and a Titanium Alloy

    pp. 690-695

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    The studies on surface morphology of an anodically oxidized pure titanium and a titanium alloy (Ti-15V-3Cr-3Sn-3Al). as well as its changes during vacuum heat treatments, were carried out in order to obtain an improved bonding ability of the surfaces of these materials. The anodically oxidized titanium and the titanium alloy showed oxide films accompanied by the numerous holes and grooves, respectively. These oxide films included phosphorus which is a constituent of the solution used for the anodic oxidation. During the vacuum heat treatment at higher temperatures, such as 1173K, the oxide films disappeared by diffusion of oxygen atom into the titanium bulk which has a large oxygen solubility. At the same time, Ti3P particles were preferentially precipitated in the holes or grooves. It is worth to note that, these specimens showed appreciably higher bonding strength than the original materials polished by #150 polishing paper. Such an improvement of these specimens in bonding strength presumes to be the results of anchoring effects of the glue in the holes and grooves of the surfaces.
  • Effects of Magnetic Field on the Growth of α-Fe Particles in a Single Crystal Cu Matrix

    pp. 696-701

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    The effects of magnetic field on the growth of ferromagnetic α-Fe precipitate particles in Cu-1.53mass% Fe alloy single crystals have been examined by the magnetic anisotropy measurement. Specimens aged at 973K for 24h were deformed in tension along the [419] direction to induce the γ→α martensitic transformation in dispersed small Fe precipitate particles. After deformation and successive annealing at 973K under the magnetic field of 1.25MA/m parallel to [110] and [116] for 30min8h, the magnetic anisotropy was examined by measuring magnetic torque around (331). The torque curves were analyzed theoretically by considering the crystal and shape magnetic anisotropies of the α-Fe particles. It is found that the elongation of α-Fe particles to the [110] direction by annealing is accelerated under the magnetic field parallel to [110] and restrained under the magnetic field parallel to [116]. These results can be understood by considering the magnetostatic stability of the a-Fe particles.
  • Introduction to Reaction Kinetics for Material Processing (III)

    pp. N277-N282

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  • The Half Century of the Refractory Industry

    pp. N283-N290

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