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

Tetsu-to-Hagané Vol. 72 (1986), No. 15

  • Stirring in Steel Making Process

    pp. 1977-1982

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  • The Present Situation and Future Prospects of Metal Processing

    pp. 1983-1990

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  • Present State and Prospects of Smelting Reduction Processes

    pp. 1991-2000

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  • Development and Application of Superplastic Materials

    pp. 2001-2009

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    [in Japanese]
  • Application of Iron-oxidizing Bacteria to Extractive Metallurgy

    pp. 2010-2015

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  • Swelling Behavior of the Iron Ore Pellets with Lime Stone during Reduction

    pp. 2016-2023

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    The swelling of the Brazillian are pellets during reduction is examined. In the sample pellets CaO/SiO2ratio and the amounts of CaO+SiO2 are controlled from 0 to 1.5, 0.3 to 12 wt% respectively.
    (1) The swelling ratio becomes less than 10 vol% at the reduction degree of 30% by using the pellets in which CaO/SiO2 is more than unity and CaO+SiO2 is more than 8 wt%.
    (2) The volume of slag phase in pellets decreases during reduction. The hematite phase swells, due to the producing conditions.
    (3) The higher the reduction temperature rises, the more the metallic iron swells in the beginningand afterwards the more rapidly it shrinks.
    x

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  • Production of Si-Mn Alloy Using Cold Pellets Contained Carbon Material

    pp. 2024-2031

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    The application of cold agglomeration process has been introduced for cheeper treatment of fine oresand dust recovery.
    The cold pellets contained carbon material for Si-Mn alloy was produced by newly developed NKK-CORAC (Continuous Rapid Curing) pilot plant.
    The physical properties of the pellets such as decrepitation, reduction disintegration, reducibility for direct reduction and resistivity at elevated temperatures were improved.
    The test operation for Si-Mn alloy production in 1250 KVA electric furnace using the pellets achieved remarkable decrease of electricity consumption, and nut coke consumption by coke fines in the pellets, and increase of manganese yield in metal.
    Based on the test results, a commercial plant of NKK-CORAC process producing 100 t/day of the cold pellets for Si-Mn alloy production was started up at Niigata Works in November 1983.
    Si-Mn alloy has been efficiently produced in a 25 000 KVA furnace with these cold pellets.
  • Gas Flow Analysis in Blast Furnace by Using Finite Element Method with Quadratic Elements

    pp. 2032-2039

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    A simulation of gas flow in a blast furnace was conducted by using the finite element method with quadratic elements. Vectorial form of the Ergun's equation was used for the equation of motion of gas in the packed bed. According to the variational principle, the discretization equation was derived from the equation of motion together with the equation of continuity. As for the infurnace structures required for numerical calculation, layered structure of are and coke, cohesive layer and raceway zone were taken into account. Simulation computations were carried out for some different configurations of cohesive zone and/or some different distributions of particle size. A numerical computation was performed to obtain the distributions of gas flow and pressure for the case in which the whole are layer consisted of double layers of different particle size.
    The results indicated that the finite element method with quadratic elements gave much higher precision for gas flow computation than the finite element method with the simplex elements which was used previously. This simulation model makes it possible to estimate the changes in the distributions of gas flow and pressure which are caused by change in particle size distribution or bed structure. It enables also to evaluate the effect of the fine-particle-charge on the gas flow distribution.
  • Effect of the Addition of CaO or MgO on the Reduction of Dense Wustite with H2

    pp. 2040-2047

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    Dense wustite plates containing CaO or MgO were reduced with H2 in the temperature range of 670 to 930°C.
    The wustite containing CaO was reduced topo-chemically and far faster than pure wustite. The experimental results were analysed by the unreacted core model. The observation of cross sections of partially reduced samples containing CaO makes the following clear. Reduced iron layers containing pores elongated from surface of specimen to interface and the long contact lines between oxide, metal and gasphase are produced by outward growth accelerated by the presence of CaO. It is therefore considered that the acceleration of reduction due to addition of CaO is caused by the formation of reduced iron layer with above mentioned structure.
    On the other hand, the wustite containing MgO were reduced slower than pure wustite and majorpart of the surface of specimens were covered by the dense iron film in the initial stage where the reduction rate obeys the rectilinear law. After this stage, the reduced iron phase grows up nontopo-chemically from the uncovered surface and the reduction rate of this stage is larger than that of pure wustite when it obeys palabolic law.
  • Effects of Shear Zone and Non-uniform Gas Flow on Heat Exchange in Moving Bed

    pp. 2048-2055

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    A mathematical model is developed to describe heat-exchanging condition in moving bed. The model takes account of the radial distribution of such process variables as descending velocity of solid particle, flow rate of gas, temperature of gas, temperature of solid particle, and pressure of gas.
    The heat exchange characteristics in the counter-current or co-current moving beds and in the moving bed heated internally or externally are clarified by numerical computation of the obtained model.
    Thickness of a shear zone formed near the wall and the temperature distribution in the counter-current moving beds are observed in the experiments.
    The dimensionless radius of the plug flow region, ro/R is independent of the Froud number and is proportional to (dp/D)-0.2.
    The radial distribution of the thermal flow ratio, or the temperature, can be appreciably affected by the preferential gas flow near the cooled wall and by the shear zone established. In case of the counter-current moving bed, the temperature difference between the plug flow region and the shear zone increases with the thickness of the shear zone.
  • Current Efficiency and Mechanisms of Redox Reaction of Iron at the Interface between Solid Iron and Molten Slags

    pp. 2056-2063

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    Current efficiency and current density-overvoltage relation at the electrode of solid Fe/40CaO-40SiO2- 20Al2O3 (mass%) molten slag with 0.55-10 mass% of total iron oxide were measured in Ar at 1 573 K. Pt-air/ZrO2-9 mol%MgO electrode was used as a reference electrode. The current efficiencies of Fe=Fe2++2e were 1.0 for anodic polarization within 200 mV and gradually decreased to 0.67 at 600 mV, but were zero for cathodic polarization. From the current efficiencies, it was concluded that anodic reaction was Fe→Fe2++2e including Fe2+→Fe3++e above 200 mV, and from the analysis of current density-overvoltage relation, it was estimated that cathodic reaction was the reduction of oxygen dissolved inmolten slag.
  • Rate of Nitrogen Desorption from Molten Iron by Argon Injection Together with Blowing onto the Melt

    pp. 2064-2069

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    A study was made on the rate of nitrogen desorption from molten iron by argon gas injection together with blowing onto the melt. The immersion depth of the nozzle was 4.65.2 cm. The injected gas flow rate was 5394 Ncm3/min. The oxygen contents in the melt were varied from 0.007 to 0.040%. During the experiment, the bubble formation time was measured by using a pressure pulse technique.
    The observed rates are compared with the equivalents calculated from a mixed control model. From the comparison between calculation and experiment, the effective free surface area of the melt is obtained. Under the present experimental conditions the effective free surface area of the melt is independent of injected gas flow rate and oxygen contents. It is about 2.1 times as large as the cross sectional area of the crucible. Since the ratio of the area of the gas-metal interface to the volume of the metal was very large in the present experiment, the nitrogen concentration in the melt decreased very fast to less than 0.001%. Nitrogen desorption from molten iron can be explained by the mixed control model over a very wide range of nitrogen concentration.
  • The Effect of Chemical Composition on the Center-line Segregation of Continuous Casting Slabs

    pp. 2070-2077

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    The effect of chemical composition on the center-line segregation of continuous casting slabs have been studied using the simulated cast ingots. The ingots were hot-rolled and were examined mainly by means of EPMA.
    Segregation of alloying elements is mostly determined by the alloy partition between molten steel and δ-ferrite phase as well as the diffusion in δ-ferrite region, and decreases with increasing temperature difference between solidus and that of -γ-phase nucleation, i.e., temperature width in δ-ferrite region. Thus the segregation of P is the largest because of the small partition co-efficient in δ-ferrite, and the increase of C content enhances the segregation due to the reduction of δ-ferrite temperature range. The segregation behaviours of Ni, Mo and Cr are also discussed.
  • Application of Vibration during Solidification of Steel

    pp. 2078-2084

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    In order to clarify the influence of vibration applied during solidification and the effect of mold wallconditions on ingots, rolled steel and weld zone, some experiments were conducted on steel specimens(SM41, SM50, and Fe-3.5%Ni). The following items were revealed through these experiments:
    (1) Content of equi-axial crystalline grains increase and their grainsize arerefined by vibration(horizontal circular vibration, 0.3 mmp-p, 60 Hz).
    (2) These effects are enhanced when the mold wall is replaced by silicon nitride.
    (3) The change in crystalline structures caused by application of vibration disappears when the ingots are rolled. (4) Steel sheets rolled from the ingots solidified under application of vibration are inferior intoughness. (5) Application of vibration during solidification has no effect on the properties of the heat affected zone of welded areas (6) In most cases, vibration during welding does not affect the properties ofthe welded metal.
  • A Study of Crack Initiation of Refractories by Cold Model Test

    pp. 2085-2090

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    A cold model test was made to simulate a crack behavior of cylindrical refractory structure. In the test, high-alumina (Al203 90%) rectangular prism bricks were used. Strain was induced by mechanical loading. Srain state was simulated to that of bricks in a cylindrical furnace in which thermal expansion of refractories are constrained by shell.
    Y-directional strain state which was given to the bricks partially and varied linearly (maximum value;ε>yo)corresponded to circumferential strain state of bricks of the furnace, and y-directional partial loading resulted in the tensile strain in x-direction (maximum value; εxm) which corresponded to radial strainof bricks of the furnace.
    Also, three point bending test of square section bar and compressive test of cylinder were carried outto get tensile critical strain (εbt) and compressive one (εbc).
    Results are summarized as follows:
    1. Cracks may be caused by εyo and εxm.
    2. Critical strain to cause cracks in cold model test, has good correlation with E εbt or εbc
  • Effects of Impurity Elements on Creep Embrittlement of Low Alloy Steels

    pp. 2093-2100

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    The influences of impurity elements on the creep embrittlement were investigated for synthetic heat affected zone (HAZ) of l 1/4 Cr-1/2 Mo and C-1/2 Mo steels.
    The creep embrittlement, the decrease in creep rupture elongation was greater with larger CEF (Creep Embrittlement Factor), which was proposed by Gooch and his coworkers for the effect of impurity elements on the propagation rate creep cracking.
    CEF=P+2.4As+3.6Sn+8.2Sb (wt%)
    Addition of a small amount of rare earth metals or Ca to l1/4 1/2 Mo steel decreased remarkably the creep embrittlement of the synthetic HAZ due to decrease of impurity elements segregation to the grain boundaries.
    Commercial 1 1/4 Cr- 1/2 Mo steel added with 0.004% Ca indicated an excellent resistance to the creep embrittlement in the synthetic HAZ. While it maintained the mechanical properties of the original material. Furthermore, the influence of hydrogen atomosphere on the creep embrittlement was investigated for the synthetic HAZ of C- 1/2 Mo steel. It was found that hydrogen decreased markedly the notch creep rupture strength, another indicator of the creep embrittlement, unless it was subjected to a post weld heat treatment. The decrease was more remarkable increase in hydrogen pressure.
  • Strength and Ductility of Ferrite-Bainite-Martensite Steels

    pp. 2101-2108

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    The influence of the bainite structure and the ratio of the volume fraction of bainite fB to that of total second phase f on the tensile properties was investigated in the ferrite-bainite-martensite steels with f=0.11-0.33.
    (1) Continuous yielding, low yield ratio of around 0.4 and the best combination of tensile strength and total elongation were achieved in the ferrite-upper bainite-martensite steel with fB/f=0.2-0.7. This steel will have much superior stretch formability to that of ferrite-martensite steels.
    (2) Ferrite-bainitic ferrite steel excluding martensite islands (fB/f=1.0) had high yield ratio of about 0.7 and relatively good combination of tensile strength and total elongation compared with other ferrite-bainite steels.
    (3) Deformation model for the ferrite-bainite-martensite steels, which was composed of the stages of preferential yielding of the ferrite, successive yielding of the bainites and yielding of the martensite, was proposed to explain the interesting tensile properties.
  • Influence of Solution Treatment under Unrecrystallized Austenite (Unrecrystallized Solution Treatment) on Strength and Toughness of 18%Ni Maraging Steel

    pp. 2109-2116

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    An addition of small amount of boron, at most several tens ppm, to 18%Ni maraging steel raised remarkably the recrystallization temperature of reversely transformed austenite up to about 1 200 K. This effect of boron addition was utilized to solution treatment of 18%Ni maraging steel under unrecrystallized austenite. It was shown that martensites transformed from unrecrystallized austenites, which contain a numerous number of dislocations, have a marked quality for their high strength and toughness. In consequence, solution treatment under unrecrystallized austenite was found to be a promising heat treatment to improve the mechanical properties of 18%Ni maraging steel.
  • Effect of Sulphur and Phosphorus on the Toughness of Carburized Steel

    pp. 2117-2124

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    The effect of sulphur and phosphorus content on the toughness of carburized SCM420 steel was studied. At first, charpy impact test was conducted using 0.8%C-1%Cr-0.2%Mo steels which simulate the case of carburized SCM420 steel to evaluate the crack initiation resistance.
    With increasing phosphorus content, charpy impact energy decreases, which is associated with the increase in intergranular fracture ratio. Auger electron analysis showed that phosphorus segregated to prior austenite grain boundaries in phosphorus doped steels. Furthermore, sulphur forms manganese sulphides elongated in the forging direction and deteriorates the toughness in the transverse direction.
    Next, charpy impact tests for hardened and tempered SCM420 steel were carried out to estimate the crack propagation resistance of core. It was revealed that only sulphur reduces charpy impact energy. It was further shown through charpy impact test for carburized SCM420 steel that phosphorus deteriorates the toughness of the case whereas sulphur reduces that of the core.
  • Three-dimensional Image Analysis of Corrosion Fatigue Fracture Surface

    pp. 2125-2132

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    Computer image processing technology has been applied to fracture surface analysis, and the generalized software for 3-dimensional fractography -image analysis has been developed. By this software, it became possible to obtain 3-dimensional fracture surface topography from a stereo-pair of SEM fractographs with sufficient precision. As for the identical position search algorithm to calculate the fracture surface height, the SSDA method was fitted to fatigue fracture surfaces in air and in vacuum. Whilst the correlation method must be applied to the corrosion fatigue fracture surface being adhered corrosion products or calcareous deposits on it, as well as to the inter- and transgranular mixed one. The crack closing simulation by means of the 3-dimensional fracture surface topography accounted for the wedge effects induced by the corrosion products or deposits as a first approximation. And the results was corresponded to the shape of load-strain hysteresis loops well. On the contrary, fracture surface roughness deduced from the 3-dimensional topography was not necessarily corresponded to the crack closing behavior.
  • On Accuracy of Measurement of Dynamic Elastic-Plastic Fracture Toughness by Instrumented Charpy Test

    pp. 2133-2140

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    It had been developed in the previous study that dynamic elastic-plastic fracture toughness parameters Jd and Tmat could be evaluated from Instrumented Charpy impact test. However, to popularize this method, strict neasuring method and judging standard on validity of obtained values must be established. One old and important problem to be clarified is a relationship between an instrumented energy (Et) obtained from area under a load-deflection curve and a dial reading energy (Er) calculated from a potential energy of hammer.
    The purpose of this study is, therefore, to solve this problem at first and also to clarify the dynamic phenomena accompanying with the measurement of load-deflection curve. It is concluded that the energy condition necessary for test without changing the load-deflection relationship is E0(applied energy)≥ 3E(total absorbed energy). This is the necessary condition to evaluate meaningful values of Jd and tearing modulus (Tmat). Moreover, it is shown how the vibrational wave superimposes the load-deflection curve analyzing the vibrational mode shape of the hammer.
  • Al2O3-SiO2系焼結体のCaO-Al2O3-SiO2系溶融スラグによる侵食

    pp. 2141-2143

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    [in Japanese]
  • コンピューターは神様です?

    pp. 2146-2146

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  • 抄録

    pp. 2149-2150

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