Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 75 (1989), No. 2

  • Utilizable and Interesting Technology of the Differential Speed Rolling

    pp. 205-212

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  • Serrated Deformation of Metallic Materials at Very Low Temperatures and Its Computer Simulation

    pp. 213-220

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  • Manufacture and Mechanical Properties of Blended Elemental P/M Titanium Alloys

    pp. 221-227

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  • Structural Analysis of the Void in Iron Ore Sinter Cake

    pp. 228-234

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    Physical properties of sinter cake such as strength and permeability are strongly related to its structure. In this investigation, the three-dimensional structure of voids in sinter cake was quantified using an image analyzer. The physical properties were then compared with the measured structural parameters.
    The results obtained are of a preliminary nature and the interpretations are tentative. However, a possible way to evaluate sinter strength was identified, which utilizes the measured values of void fraction and the size distribution and shape factor of the voids. The work also showed that when a sinter cake is considered to be a packed bed, the apparent diameters of the particles used for estimating heat exchange rates between gas and solid and pressure drop across the bed are different for the two purposes.
    A theoretical analysis of the magnitudes of forces acting on granules was made to identify the causes of the rearrengement of a bed during sintering.
  • Two Dimensional Analysis on the Formation Process of Burden Distribution at Blast Furnace Top

    pp. 235-242

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    The formation process of the burden distribution at blast furnace top was dynamically and quantitatively investigated by the use of a two-dimensional mathematical model, in which the equations of motion on each particle were approximated by a rheological model. In order to increase the estimation accuracy of the model, the dashpot factor, which represents the kinetic energy dissipation during the formation of the burden distribution, was experimentally determined.
    The following knowledge was obtained through the application of the model.
    The slope angle has significant influence on the burden deposit behavior throughout the charging. The size segregation phenomenon on the slope can be quantitatively evaluated by the model. The change of the charging condition of small particles onto the slope results in the change of the small particle distribution on the slope as well as the change of the deposit profile. The decrease of charging rate caused by the increase of charging time reduces the thickness of the flowing layer of particles to result in the enhancement of the sieving of small particles on the slope.
  • Measurement on the Region in and around the Raceway in a Blast Furnace by Use of a Sideways Tuyere Probe

    pp. 243-250

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    A sideways tuyere probe has been developed to measure in and around the raceway and deadman region in the blast furnace in operation. The probe was installed at No.5 blast furnace in Chiba Works. The probe has the advantage that it does not introduce any disturbance in the raceway phenomena because the probe is driven 3m into the furnace with an oblique angle to the tuyere axis through the No.25 tuyere adjacent to No.24 tuyere that is to be observed.
    Measurements were mainly carried out to investigate chemical composition of gas, coke and molten materials, temperature profile and fluid dynamics in the vicinity of the raceway region. Results obtained are as follows:
    (1) The combustion in and around the raceway occurs symmetrically both to the deadman and to the side direction of the raceway.
    (2) Change in raceway depth with the blast condition can be estimated with HATANO'S equation.
    (3) The silicon content of dripping metal is high in the interior of the raceway while outside it is almost the same level as that of tapped metal.
    (4) High (FeO) slag which is oxidized by the blast oxygen exists within the raceway.
  • "In-situ" Analysis of High Temperature Gases by Infrared Spectroscopy and Its Application

    pp. 251-258

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    A technique for the "in-situ" analysis of the high temperature gases containing CO, CO2, H2O and SiO at 800-1 600°C was developed. The gas in the furnace was monitored by a newly developed infrared optical sensor with Fourier Transform Infrared Spectrometer (FTIR). The sensor was of a water cooled probe with various infrared light guide.
    The experimental results could be summarized as follows;
    (1) Partial pressure of CO, CO2 and H2O could be measured at 800-1600°C by the infrared optical sensor. The maximum sensitivity of this technique was as high as 0.0001atm (100ppm) of CO gas with optical depth of 200mm at 1 550°C.
    (2) Infrared absorption spectrum of unstable SiO gas was measured by the infrared optical sensor demonstrating the possibility of measuring the partial pressure of SiO.
    (3) It was demonstrated that those gas species evolved during the reduction of cold-bonded pellet by CO or H2 gas was quantitatively analyzed.
    (4) "In-situ" analysis technique was applied to the pilot plant scale combustion test furnace. Change of gas composition with pulverized coal injection could be accurately monitored in the combustion furnace.
  • An Application of Oxygen Ionic Conductivity of Zirconia to Metal-Zirconia Joining

    pp. 259-266

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    A new joining method has been developed which is applicable to metal-zirconia systems.
    This method has the following advantages;
    1. Ability to make joining without load,
    2. Ability to make joining in a short time,
    3. Ability to make joining to any surface area,
    4. No oxidation of the metal surface,
    5. Ability to control the thickness of the reaction layer,
    6. No special equipment is required,
    7. Ability to be used even with complex shapes,
    8. Ability to be used with zirconia sprayed materials.
    In the present work, chiefly, an Fe-zirconia system was investigated and it was confirmed that this method was applicable to other metal-zirconia systems.
  • Behavior of Components in the Molten Iron from the Trough Type Continuous Steelmaking Furnace

    pp. 267-274

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    In the operation of continuous steelmaking plant (CSM process) manufacturing low carbon steel (0.18% C), temperature and analyses of various components, in addition to carbon, of molten iron have been obtained at the cupola outlet and at the steelmaking furnace outlet every 30 min. succesively for more than 24 h. Behavior of the components in the molten iron at the steelmaking furnace outlet was investigated concerning to the mean value and the variation of the data taken at that occasion. Principal results are as follows:
    (1) 88-94% of oxygen supplied were consumed for decarburization. Mean value of Mn and P in molten iron were close to their equilibrium concentration with slag, while Cr content in molten iron was less than that deduced from slag composition.
    (2) Variation at outlet was composed of 3 factors; contribution of inlet variation, effect of oxygen flow rate and variation brought about in the furnace. Influence of inlet variation on outlet variation was neglegible for C and temperature, considerable for Cr, Mn and P, and predominant for Ni and Cu. An increase of oxygen flow rate decreased C. but raised Cr. Mn. P contents as well as metal temperature at outlet.
  • Automatic Casting Method of Twin Belt Type Thin Slab Caster

    pp. 275-281

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    For the stabilization of operation and improvement of quality in twin belt type continuous casting process adopting overflow type pouring method, an automatic casting start method and a pool level control method have been developed on the following procedure.
    (1) In the casting start stage, the flow rate of molten steel poured from large tundish into small tundish is estimated based on the measured change of small tundish weight. Required opening degree of sliding gate, casting speed and change timing of casting speed are calculated by using the above mentioned molten steel flow rate. Casting start is operated automatically by this method.
    (2) After the automatic casting start, pool level in the caster is controlled by the change of casting speed, and at the same time the deviation of casting speed is reduced by the operation of opening degree of sliding gate of large tundish. Pool level control is operated automatically by this method.
    The automatic casting method is being put into practice, and brings the smooth casting start and improvement of control accuracy of pool level.
  • Characteristics and Outline of the New Continuous Furnace with Low Thermal Inertia in the Kimitsu Plate Mill

    pp. 282-289

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    We newly developed and established the high efficiency continuous reheating furnace with low thermal inertia in the Kimitsu plate mill, in order to adopt to the needs for perfect HCR (Hot Charged Rolling), TMCP (Thermo Mechanical Control Process), and energy conservation.
    Through the adoption of ceramic fiber as lining material for the furnace body, skids, partition walls and heat cover plates over the hearth opening, this furnace realizes low thermal inertia and reinforcement of thermal insulation, and also makes heating schedule free.
    In adition, by adopting high turn down burners, cyclic combustion control and a, high precision temperature calculation model, this furnace is superior in relation to slab temperature with the high precision uniformity.
  • Influence of Microstructure of Coating on Corrosion Resistance of Zn-Al Alloy Coated Steel Wire Manufactured by Double Hot-Dip Process

    pp. 290-297

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    In order to clarify the relation between the microstructure and the corrosion resistance of coating for the Zn-Al alloy coated steel wire manufactured by the double hot-dip process, the corrosion behavior of the alloy coated steel wires in the salt spray test has been investigated by varying the aluminum content of coating, the cooling conditions after coating, the reduction of area by drawing, and the bluing temperature after drawing.
    (1) The eutectoid phase, which contains approximately 22 mass per cent aluminum and consists of the fine complex mixture of α-Al phase and β-Zn phase, has the dominant effects on the corrosion behavior of the Zn-Al alloy coating.
    (2) The preferential corrosion occurs along the boundaries such as β-Zn primary crystals/eutectic phase, β-Zn matrix/eutectoid phase, and eutectic colony boundaries.
    (3) The corrosion of the β-Zn phase is preceded by that of the eutectoid phase.
    (4) The corrosion rate of coating increases with the increase in the cooling rate after coating.
    (5) Either the eutectic structure or the primary dendrite structure grows along the direction of solidification of coating as the cooling rate increases. These structures of the uniform direction from the surface to the base metal are considerd to accelarate the corrosion along the preferential corrosion paths resulting in the deterioration of the corrosion resistance of the Zn-Al alloy coating.
  • Microstructure and Corrosion Behavior of Intermetallic Layer of Coating in Zn-Al Alloy Coated Steel Wire Manufactured by Double Hot-Dip Process

    pp. 298-305

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    A study has been made on the microstructure and the corrosion behavior of the intermetallic layer of the Zn-Al alloy coating by immersing the conventionally galvanized steel wire in a Zn-Al alloy bath containing 3 to 10 mass% aluminum.
    (1) The Zn-Al alloy coating by the double hot-dip process has duplex coating layers. The outer coating layer has the same chemical composition as the alloy bath and the intermetallic layer, which is formed by the diffusion of aluminum from the alloy bath into the Zn-Fe intermetallic layers of the galvanized wire, has a higher content, i. e., approximately 30 mass%, of aluminum than the alloy bath.
    (2) The microstructure of the intermetallic layer of the Zn-Al alloy coating consists of the Zn-Al alloy matrix of the quasi-eutectoid phase and the fine, plate-like precipitates of Fe4Al13 containing some amount of zinc.
    (3) The intermetallic layer of the Zn-Al alloy coating exhibits such good drawability that the total reduction in area by drawing can be increased to over 80.9% without any crack occurrence.
    (4) The first rusting time of Zn-Al alloy coated steel wire in the salt spray test is over four times longer than that of galvanized wire, and the high corrosion resistance is unchanged after drawing.
  • Effect of Alloying Elements on the Corrosion Resistance of Austenitic Stainless Steels in Nitric Acid Containing Highly Oxidizing Ions

    pp. 306-313

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    Stainless steel has good corrosion resistance in nitric acid. When the corrosion potential is in transpassive region, however, the resistance tends to be decreased according to the oxidizing environment. In this study, the effects of alloying elements such as Mo, Nb, Ti, Zr, Si, Cr and P were investigated on the corrosion resistance of the austenitic stainless steel in the transpassive region, i. e. 40%HNO3 + 0.2 g/1Cr6+. The corrosion of welded joint was also examined. The results are as follows.
    (1) Si was the most effective element for corrosion resistance improvement in highly oxidizing nitric acid, while Mo, Nb, Ti and Zr were not effective. (2) Si improved the corrosion resistance in highly oxidizing nitric acid solutions containing Cr6+ ions by suppressing cathodic reaction and by mitigating the detrimental effect of P segregated intergranularly. (3) The corrosion resistance of high Si steel was inferior to that of low Si steel in pure nitric acid, where the steel is in the passive region. On the other hand, Cr showed reverse effects, i. e., improvement of the corrosion resistance in passive potential region, and little effect in transpassive region. (4) Weld metal of Si-bearing austenitic stainless steel corroded severely due to the formation of the intermetallic compounds and segregation of Ni, Si and Nb.
  • HIP Sinterbility of Silicon Nitride α→β Phase Transformation

    pp. 314-320

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    The effects of β phase transformation on HIP sinterbility of silicon nitride were studied using three different powder sizes. The influence of pressure, temperature and holding time on the sinterbility of silicon nitride powders were also investigated.
    In order to examine the sintering process, HIP sintering experiments were also conducted under conditions to produce low densities of the sintered bodies. The HIPping conditions were 1 723-1 973 K, 60-200 MPa, holding time 0-3 h, and alumina as well as yttria were used as additives up to 6 mol%.
    Within the range of the present work the following was revealed:
    (1) The relative density changes linearly with the phase transformation at the initial stage of HIP sintering. At the final stage of HIPping, the phase transformation to β advances drastically faster than the densification does.
    (2) Phase transformation to β is mostly affected by the HIPping temperature, and next by the holding time.
    (3) The HIPping pressure has little influence on the β phase transformation, and sometimes reduces the phase transformation.
    (4) Fracture toughness improves with the increase of the β phase content. Micro hardness is highest around 40-50% of the β phase fraction.
  • Effects of C and Mn Contents and Heating Rate on Recrystallization Texture of Al-killed Sheet Steels

    pp. 321-328

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    Al-killed steels containing various amounts of C (6 to 580 ppm) with two levels of Mn, and extra-low C, high Al and N steels containing various amounts of Mn (0.15 to 0.78%) were cold rolled and annealed at a heating rate between 20°C/h and 50°C/s for the investigation of recrystallization textures. The following conclusions were obtained:
    (1) When steels were annealed at a slow heating rate, there existed an optimum C content which resulted in a large elongated grain structure and weak {110} and {100} and strong {111} texture components after recrystallization. The optimum C content shifted to a lower level with increasing heating rate, and was thought to be related to the optimum heating rate.
    (2) The optimum heating rate for obtaining large elongated grains became higher with decreasing C content. Two new empirical formulas, dependent on the Mn content, relating the optimum heating rate with the chemical compositions of C, Mn, Al and N were proposed. These formulas can also be applicable to the case of rapid heating, such as for continuous annealing.
    (3) Under the optimum heating condition, the large elongated recrystallized grain structure was always accompanied by weak {100} texture component but that was not always accompanied by weak {110} and strong {111} texture components. Therefore the essential role of AlN precipitates during heating at the optimum rate is to inhibit the recrystallization of {100} deformed matrices.
  • Properties and Carbide Morphology of Austenitic Stainless Steel Processed by Controlled Rolling and Accelerated Cooling

    pp. 329-336

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    This paper surveys the application of controlled rolling and accelerated cooling process-(thermomechanical control process=TMCP)-to austenitic stainless steels (AISI304, 304L, 316, 316L). The TMCP makes it possible to produce high-strength stainless steels while retarding carbide precipitation at grain-boundaries. The high strength is achieved by refining microstructures, and the ausforming effect which increases dislocation density. The 10% oxalic acid test reveals that, a sensitized TMCP type 304L does not easily form a ditch structure. The ferric sulfate-sulfuric acid test shows that the corrosion rate relating to chromium depleted zones of the TMCP type 304L is equal to that of the solutionized one. In a sensitized TMCP type 304L, sheet-like M23C6 carbide precipitates dispersively at grain-boundaries and subgrain-boundaries of the un-recrystallized grain. This is very different from the continuous precipitation at grain-boundaries in solutionized stainless steel. It is presumed that the dispersed precipitation leads to a discontinuous chromium-depleted zone and as a result, the sensitized TMCP type 304L does not form a ditch structure.
  • Effects of Cold Rolling and Annealing on the Anisotropies and Texture Formations in an 18 % Ni (350) Maraging Steel

    pp. 337-344

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    The effects of cold rolling on anisotropies in tensile properties and the second formability have been investigated on an 18%Ni (350) maraging steel. The following results were obtained.
    (1) The rate of strain hardening was different among the rolling directions. That is, the plot of the tensile strengths against the longitudinal, 45 degree-declined, and transverse directions, showed a V-shape. This shape almost remained unchanged after aging treatment.
    (2) The origin of the anisotropies was considerd to be the increase in the density of {113} <110> orientation.
    (3) Recrystallization texture was formed by solution annealing after cold rolling. This recrystallization texture was similar to that of α-iron, in spite that the maraging steel had experienced the martensite to austenite reverse, and austenite to martensite transformation. This phenomenon suggested that the specified variants were preferred in the transformations.
    (4) The second formability measured by Erichsen test was increased by the development of {111} <112> texture.
  • Effects of Vanadium on Hot Ductility of High Carbon Steels

    pp. 345-352

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    Effects of V on hot ductility of a high C steel have been investigated by means of hot tensile testing in relation to hot cracking on the continuously cast slab surface. The ductility of the specimens initially solution-treated at high temperatures is largely reduced in slow strain rate deformation at temperatures ranging from γ/α duplex to low temperature γ region. The ductility trough with the minimum value at temperatures just below the Ae3 points, which are significantly lower than those in low C steels, is deepened and widened into high temperature region of 950°C by small amount of V addition. The embrittlement in γ region can be explained in terms of V(C, N) precipitation during the slow strain rate deformation ; strain concentration within soft precipitation-free zones along γ grain boundaries induces microvoids by decohesion of densely line-uped precipitates at the boundaries from the matrix, and leads to the final fracture by their coalescence. The intergranular ductile fracture in γ/α duplex phase region can be caused by the strain concentration in soft ferrite layers along γ grain boundaries in addition to the effect of the dynamic precipitation of V(C, N). Ductility improvement with an increase in the strain rate can be explained from V(C, N) precipitation and/or ferrite formation during deformation.
  • Change in Mechanical Properties with Stress Relief Annealing in Pressure Vessel Steels

    pp. 353-360

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    Prolonging annealing treatment below the critical temperature is carried in order to relieve residual stress due to welding and to improve toughness of weld heat affected zone in the fabrication of pressure vessels. It has been known that this treatment named stress relief (SR) annealing decreases strength and toughness of base metals. Thus, the effects of microstructure and alloying elements on this decrease in mechanical properties were investigated in carbon-manganese, manganese-molybdenum and chromium-molybdenum steels for pressure vessels.
    The decreasing amount of strength and toughness due to SR annealing was the largest in martensite structure and next in bainite structure. These was little change in strength and toughness in ferrite-pear-lite structure. Good toughness was obtained by SR treatment at high temperature and for short time in comparison with that of low temperature and long time at a certain strength. The start of decreasing toughness was delayed by an increase in {1/5 (Mn(%)+ Cr(%))+Mo(%)} content.
    Applied stress equivalent to residual stress level in SR treatment did not affect mechanical properties. The amount of temper embrittlement due to slow cooling in SR treatment decreased with prolonging SR treatment.
  • Relationships between Stress Relief Embrittlement, Microstructures and Fracture Appearances in Pressure Vessel Steels

    pp. 361-368

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    It has been known that degradation of toughness in steels accompanying with a decrease in strength occurs in prolonging stress relief (SR) annealing during the fabrication of pressure vessels. This degradation of toughness was named SR embrittlement. The relationship between SR embrittlement and microstructure and fracture appearance was investigated in 1.5Mn, 1.5Mn-0.5Mo, 0.5Mn-1Cr-0.5Mo and 0.5Mn-2.15Cr-1Mo steels heat-treated to martensite structure. SR annealings were carried out at 600 to 725°C.
    Carbide size, inter-carbide distance and subgrain size were increased with the progress of SR annealing. Increases in manganese, chromium and/or molybdenum suppressed the growth of carbide and subgrain and caused to retard SR embrittlement.
    SR annealing did not change cleavage facet size of Charpy impact fracture surface except for Mn-Mo steel, but increased the distance of tear ridge within cleavage facets in all the steels. The amount of plastic deformation, measured by X-ray line broadening, in cleavage surfaces was decreased by SR annealing.
    It is considered that SR embrittlement is mainly caused by a decrease in cleavage fracture strength due to decrease in plastic work done for crack extension. The decrease in plastic work was induced by an increase in distance of a substructure boundaries related to the formation of tear ridge. Since cracking of carbides themselves or cracking between carbides and matrix occur in a steel containing carbides of more than 1 μm in diameter, that also decreased cleavage fracture strength and then caused SR embrittlement.
  • アメリカの知的所有権主張の科学技術的背景

    pp. 378-378

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