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

Tetsu-to-Hagané Vol. 82 (1996), No. 1

  • A Study on the New Iron Ore Smelting Reduction Processes

    pp. 1-7

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    A study on the DIOS process (Direct Iron Ore Smelting Reduction Process) has been undertaken by the Japan Iron and Steel Federation as an 8-year project which began in April 1988.
    A pilot plant with a production capacity of 500 tons of hot metal per day was constructed at NKK Keihin works.
    The operating tests of pilot plant started in October 1993, and eight campaigns were successfully conducted by August 1995 as planned.
    This report introduces an outline of the pilot plant and some results of the operating tests.
  • Engulfment and Pushing of Foreign Particles Such As Inclusions and Bubbles at Solidifying Interface

    pp. 8-14

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    Previous studies on the behavior of particles at an advancing solid-liquid interface were critically reviewed on the following points : 1) physicochemical feature of the advancing interface-partical system, especially the interface shape in relation to solute concentration in the liquid and the difference in thermal conductivity between particle and liquid, etc., 2) forces of buoyant, viscous drag, Saffman, van der Waals and interfacial tension gradient acting on the particle in the vicinity of the advancing interface, 3) theoretical treatises on the description of critical velocity Vc as a function of various factors of the system, particles are engulfed by the interface advancing at the rate larger than Vc, 4) experimental results on Vc in relation to particle radius, interface shape, viscosity of the liquid, temperature gradient in the liquid, free energy change in the transfer of particle from liquid to the solid phase, heat diffusivities of particle and liquid, solute concentration of the liquid and volume fraction of particle at the interface.
  • A New Approach to Materials Design and Development for Advanced Materials : Interfacial Architecturein Material Systems

    pp. 15-22

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    A new approach to materials design and development for advanced materials is discussed which is defined Interfacial Architecture for material systems. Structure-dependent properties of individual grain or interphase boundaries can be effectively utilized to produce a polycrystal system with high performance by designing and controlling the grain boundary character distribution (GBCD). Recent applications of the concept of Interfacial Architechture through grain boundary design and control for advanced materials are introduced. A prospect of materials design and development by Interfacial Architecture is discussed.
  • Mechanism of the Non-uniform Sintering on Using a Low-Al2O3 Pisolite Ore

    pp. 23-28

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    Increasing a usage of the pisolite ore in a sinter plant often results in a decreased yield and strength of the product. These negative features are anticipated to be caused by the formation of the non-uniform sintered layer at the middle or on the bottom part of the sintered ore bed, where sometimes the low-Al2O3 pisolite ore is richly distributed.
    The low-Al2O3 pisolite ore, the so-called easily "fusible ore", due to its high assimilation rate, produces a large amount of melt with very low viscosities which directly contributes to forming the excessively dense structure and deteriorating the gas permeability, especially in the lower part of the ore bed, and then leads to the decreased production yield.
    In the present study, it was clarified that the "fusibility" control of ore layer and the viscosity control of the formed melt could be the effective countermeasures to prevent the non-uniform sintering. It was also suggested to maintain the ratio of the low-Al2O3 pisolite ore to the infusible ore constant throughout the ore bed in order to attain the proper gas and melt distributions inside the ore bed and therefore to improve the operation performance.
  • Experimental and Numerical Analysis on the Movement and the Accumulation of Powder in the Deadman and the Dripping Zone of Blast Furnace

    pp. 29-34

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    The powder-gas 2 phases flow experiment using parallel packed beds was carried out in order to quantitatively analyze the powder movement and the accumulation in the lower part of blast furnace, and powder penetration to the deadman. The powder mass velocity and powder hold-up are strongly influenced by the gas velocity, the powder diameter and the injection amount. Especially, in the low gas velocity condition, the powder mass velocity decreases and powder hold-up increases.
    Powder accumulation is so much in the coke powder of the larger diameter, rather than the pulverized coal.
    The new equation of motion concerning the powder movement was derived. Which is taken into account of the friction as a interaction force between powder and coke. Furthermore, new numerical equation which can estimate powder hold-up under the blast furnace operating conditions was proposed
  • Estimation of the Formed Position of the Surface Cracks on the Slab in the Continuous Caster

    pp. 35-40

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    When surface cracks on continuously cast slab were observed by a microscope, internal oxidation layers were sometimes present along the cracks. Attention was paid to these layers which are called subscales for the estimation of the formed position of the surface cracks in the continuous caster.
    First, the subscale was formed on the test sample in the laboratory under the cooling condition of the continuously cast slab. Second, some kinds of cracks on the continuously cast slabs were collected, observed by a microscope and compared with the subscale of the former samples.
    The results are summarized as follows.
    (1) The thickness of the subscale for the formed position in the continuous caster was calculated by the combination of the internal oxidation theories and the cooling curve of the slab.
    (2) The formed position of five kinds of cracks were considered as follows.
    (i) The small longitudinal crack was formed in the mold and enlarged in secondary cooling zone.
    (ii) The horizontal crack had the initiation point of crack existing in the secondary cooling zone and was enlarged at the unbending point.
    (iii) The star crack and C-crack were formed in the mold or just under the mold.
    (iv) The edge crack was formed at the unbending point.
  • Slurry Wear Test Using Galvanic Cells

    pp. 41-46

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    Several kinds of steels were subjected to slurry wear tests using a electrochemically instrumented apparatus which consisted of a rotating cylindrical disc attaching four samples with various Galvanic couples. Each sample were rotated in a slurry of quartz sand (50%) and water. Abrasion behavior was determined by weight loss and observed by scanning electron micrography as functions of hardness and chemistry. The effect of electrochemical behavior on slurry wear could be evaluated by means of various Galvanic couples. Its abrasion depended not only on hardness of steels but also on potential difference between them, so that slurry wear was suppressed by cathodic protection. Abrasion resistance was improved by increasing hardness HRC and chromium content and decreasing carbon content and potential difference E, and the regression equation describing these effects on erosion loss EL was obtained as follows;EL=-1.58HRC+4.65%C-4.82%Cr+0.073E(mV)
    x

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  • Determination of Nitrogen in Steel by Spark Emission Spectrometry

    pp. 47-52

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    A co-laboratory research was carried out in order to apply the spark emission spectrometry to the determination of nitrogen in steel. The atomic emission line of nitrogen at 149.263 nm is used as the analytical line. It is found that the conventional types of spark emission spectrometer is considerably useful to determine nitrogen concentration in steel down to 20 ppm level with rather high precision the sensitivity represented as BEC value is 350 ppm, and the analytical precision is 2ppm (1σ) at 20 ppm level. Spectral interferences originated from Fe(II) 149.258 nm and Si based continuous emission are found, but there is no interference from the possible metallic elements such as Cr, Ni, Mo, and Mn. Those ieterferences can be easily corrected by the co-existing elements correction method, in which the correction factor of Fe is 0.00013 × [Fe] % and that of Si is 0.007 x [Si] %. There is no effect of co-existing Ti on the sensitivity and the analytical precision of nitrogen determination, because the TiN may not grow enough to disturb the normal sparks in these heating pretreatment conditions. Grain size of sample has no effect on nitrogen determination. This point is of great advantage to its application to the ladle analysis. It is because the microstructure is strongly affected by sample heating and quenching patterns and is quite different from sample to sample at the production site.
  • Development of On-line Analysis Method for Determination of Chromium in Molten Stainless Steel in LD Converter

    pp. 53-57

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    An on-line analytical method based on the hotspot radiation spectrometry was applied to the determination of chromium in molten stainless steel in a converter. In this study, the following points were discussed in order to develop an on line and real-time monitoring method for chromium concentration in molten stainless steel. The first is that the atomic emission intensity of chromium at the hotspot is expected to be weak because its atomic vapor pressure is rather low. The second is the severe self absorption effects on the chromium determination, because its concentration in the stainless steel is about 10 to 20%. The third is the possibility of the spectral interferences because there are strong emission lines of iron very close to the analytical line of chromium. Finally, the formation of the very hard slag with Cr2O3 may interfere to form the hotspot properly. Consequently, the modification of the spectral measurement system and the development of data analytical procedure make it possible to determine chromium concentration in molten stainless steel with the analytical precision of CV=7%.
  • Improvement of Seam-defects on Strip Edge of Stainless Steel

    pp. 58-62

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    On the hot strip rolling, a sizing press is installed to change slab-width in stead of the vertical edgier mill. Operation of the sizing press has enabled the number of mold width changes to minimized. This has resulted in the potential monthly throughput of the caster increasing. Moreover, especially for stainless steel grades, the side seam defect can be much reduced by applying the convex die and thus trimming loss is much improved.
    On the hot strip rolling of stainless steel grades, the side seam-defects tend to grow at the slab corner because of the temperature fall. Thus the new technique reducing the width of the side seam-defect by forming the slab edge into concave shape with the sizing press before rolling and preventing the sidthspread on rolling were investigated. The slab deformation in sizing with convex dies was analyzed by FEM simulation and the most suitable profile of the die was decided for the improvement of trimming loss because of the side seam defect.
    In this report, above simulation results of slab-deformation by sizing press are presented.
  • Effect of Small Amount of Ni on Hydranlic-descaling-ability in Si-added Hot-rolled Steel Sheets

    pp. 63-68

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    Poor descaling ability in Si-added hot-rolled steel sheets can be explained in term of anchor effect of FeO/Fe2SiO4 eutectic-compound cutting into both steel and upper FeO sides, which is formed during slab soaking. Although the uneven interface of eutectic-compound/steel can result from penetrating of liquid FeO/Fe2SiO4 eutectic-compound into γ grain boudaries, the details have not been clear so far. Thus, in this work, we have studied the behavior with particular emphasis on the small amount of Ni, which is unavoidably included in the steel making process. Reproduction tests of red scale by a laboratory 3-stand tandem-mill with descaling apparatus suggests that the uneven interface is closely related to the small amount of Ni. That is, in 1.5wt% Si-added steel which includes only 0.0034wt% Ni, eutectic compound/steel interface in primary scale is flat and no red-scale forms. Whereas, in 0.02wt% Ni steel, the interface of eutectic-compound/steel in the primary scale was quite uneven even in the case of lower Si content of 0.5%, and typical red scale was observed, resulting in poor descaling ability. Increase of Si, Mn accelerates uneveness of eutectic-compound/steel interface through the growth of internal oxides.
  • Change in Microstructure of Zn-Co-Cr-Al2O3 Composite Coating by Cyclic Corrosion Test

    pp. 69-74

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    The microstructure and chemical state of Zn-Co-Cr-Al2O3 composite coating before and after the cyclic corrosion test (CCT) were investigated by electron microscope, X-ray photoelectron spectrometer, and electron probe micro analyzer. The coating layer consisted of a Zn matrix containing super-saturated Co and dispersed particles of cohesive Al2O3, Cr2O3, Cr(OH)3 coordinating SO4. The dispersed particles existed uniformly in a regular matrix in coatings formed in electrolytes with lower concentrations of dispersed Al2O3 particles and Cr-ions, while the matrix was dendritic and the dispersed particles concentrated along the dendrite arms in coatings formed in electrolytes with higher concentrations of Al2O3 particles and Cr-ions. The main corrosion products of the composite coating after the CCT were ZnCl2·4Zn(OH)2 and ZnO, which is similar to that with conventional Zn coatings, but the amount of the Zn rust is less than that with conventional Zn coatings. Fine networks of ZnCl2·4Zn(OH)2 grew in the coating in the vicinity of the steel substrate during the CCT. A region of highly-condensed dispersed particles existed between the ZnO layer and the residual coating layer. It is considered that ZnCl2·4Zn(OH)2 formed uniformly by the local cathodic reaction of Co, and the existence of the protective region of dispersed particles gave high corrosion resistance to the composite coating.
  • Reaction Diffusion between Iron and Pb-Zn Melt at 733 to 818K

    pp. 75-80

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    Pure Fe specimens were annealed in pure Zn and binary Pb-Zn melts at temperatures between 733 and 818K for various times. The kinetics of the reaction diffusion between the specimen and the melt was examined. In the case of the pure Zn melt, the Γ, Γ1, compact δ1 and palisade δ1 phases were formed between the Fe specimen and the melt at temperatures higher than 778K, and the ζ phase as well as these four intermetallic phases was observed at temperatures lower than 768K. In the case of the binary Pb-Zn melt, however, the formation of the intermetallic phases with high zinc concentrations was inhibited with decreasing zinc content of the melt. At temperatures between 778 and 808K, fragmentation of the palisade δ1 phase occurred during the annealing in the Pb-Zn melt with zinc content higher than 40 mass%.
  • The Rules of Mixture on Physical Properties of Composite Materials with Network Structure

    pp. 81-86

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    Functionally Gradient Material (FGM) is, especially, focused as a new heat-resistant material because of its thermal stress relaxation ability. In the design of FGM, estimation methods of physical property distributions, i.e. rules of mixture on physical properties, are required, because FGM has different composition in each region.
    In this paper, thermal conductivity, Young's modulus and thermal expansion coefficient of composite materials with dispersive and/or network structure are calculated by finite element method (FEM) analyses. The results of the analyses were formulated with the volume fraction and a newly proposed geometric parameter which is correlated with the connectivity between perticles in the network structure. Thermal conductivity predicted by this formula had a good agreement with experimental value of SiO2/Fe composite materials.
  • Effect of Ni Content on High Temperature Properties of 9Cr-7Mo Steel Strengthened by Precipitation of Intermetallics

    pp. 87-91

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    Since ferritic steels strengthened by intermetallic precipitates exhibited excellent creep strength compared with any other commercial steels, they are promising core materials for advanced fast breeder reactors. It is, however, worried that their ductile-brittle transition temperature (DBTT) increases markedly during service. Therefore, in order to improve the room temperature ductility of 9Cr-7Mo steels after aging with keeping high creep strength, influence of Ni addition on them were investigated.
    The tensile properties of the specimens aged for 100h at 823K and 923K were markedly improved by Ni addition. And creep rupture strength at 923K was also improved with increasing amount of Ni addition. The α to γ transformation was partially observed in the specimens containing more than 6mass%Ni after creep testing. The formation of austenite would be effective to improve the long term creep strength, but it increases void swelling. The optimum Ni content in 9Cr-7Mo steel was approximately 3mass% for application of the fast breeder reactor core materials, considering the DBTT and the resistance to swelling.
  • Influence of Interparticle-spacing on Creep Rate in a 2.25Cr-1Mo Steel

    pp. 92-97

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    Base material and heat-affected zone (HAZ) material of 2.25Cr-1Mo steels, which had been treated to control the interparticle spacing between carbides, λ, were subjected to creep tests under a stress of 108 MPa at 923 K to clarify the correlation between interparticle spacing between carbides and secondary creep rate. On the basis of the test results, the influence of interparticle spacing on secondary creep rate was evaluated. The results of this study are as follows:
    (1) The correlation between the interparticle spacing, λ/m and Larson-Miller parameter, LMP is expressed by the following equation:
    In λ=1.0 × 10-3 LMP -37
    (2) The correlation between the interparticle spacing, λ/m and the minimum creep rate, εm/s-1 is expressed by the following equation:
    Inεm=1.8In λ+b
    where b is 15 for base material and is 12 for HAZ material.
    (3) Using the creep strain curve obtained by the calculation on the basis of change of interparticle spacing during creep deformation, the creep life of the steel is estimated with an error of about 15%.

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