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

Tetsu-to-Hagané Vol. 100 (2014), No. 11

  • Effect of Large Quantity of Ferrocoke Charging on Reduction of Reducing Agent Rate of Blast Furnace

    pp. 1347-1354

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    DOI:10.2355/tetsutohagane.100.1347

    The mathematical model which describes the behavior of ferrocoke in blast furnace was developed and incorporated into the mathematical blast furnace model. The effect of ferrocoke on the reduction of reducing agent rate and carbon rate of blast furnace was investigated with the mathematical blast furnace model.
    The effect of ferrocoke on the reduction of reducing agent rate and carbon rate depends on the ore/coke distribution of burden and operational conditions of blast furnace. High reducible sinter is required for the reduction of reducing agent rate of blast furnace by charging a large quantity of ferrocoke into blast furnaces. The gasification degree of ferrocoke calculated by the mathematical blast furnace model agreed well with the experimental results.
  • Development of Removal Technology of Attached Iron Ore Fine

    pp. 1355-1360

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    DOI:10.2355/tetsutohagane.100.1355

    Improvement of gas permeability in the blast furnace is strongly needed to realize lower coke rate blast furnace operation which can reduce CO2 exhaust dramatically. In the upper part of the blast furnace, it is known that removal of fine particles is very effective to improve gas permeability. Especially wet raw iron ore brings a lot of fine iron ore into blast furnace because the wettability of iron ore is quite higher than sinter ore, coke, and other raw materials. Then removal of attached ore fines from wet raw iron ore was tried using conventional screen. At first screening condition was changed, then it was shown that the extension of screening time was effective to remove fine ore. Next, screening of wet iron ore with additional reagent which can reduce the adhesion force by water was tested. Water absorbent polymers and surface acting agents were prepared and added to wet iron ore. Addition of these reagents was very effective to remove ore fines from wet iron ore.
  • Effect of Additives (Alumina, Magnesia or Calcium Fluoride) on Dissolution Rate of Solid CaO into Calcium Silicate Based Slags

    pp. 1361-1370

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    DOI:10.2355/tetsutohagane.100.1361

    A study was undertaken to understand dissolution behavior of solid CaO particles into molten slags. Experiments were carried out to determine the effects of the basicity (CaO (mass%) / SiO2 (mass%)) and the kinds of additives (Al2O3, MgO or CaF2) on the dissolution rate of the rotating cylindrical CaO sinter into the ternary calcium silicate based slags at 1823 K. (Contact materials: graphite, Atmosphere: Ar)
    The dissolution rate increased with increasing rotation velocity of the cylindrical CaO sinter. It was found that the dissolution rate was highest with the CaO-SiO2-CaF2 slag so that CaF2 was proved as a good flux material. The dissolution rate of CaO increased with lowering slag basicity for the all slag system. However, this tendency was found to be weaker with the CaO-SiO2-Al2O3 system than the others due to the significant viscosity increase in the lower basicity region.
    The observation of the interface between CaO and each slag indicated that the dicalcium silicate (Ca2SiO4) phase was formed for all the slag systems. Further, the additive elements of Al and Mg were condensed in the interlayer between the Ca2SiO4 and the CaO phases as the calcium aluminates and the magnesia. On the other hand, in the case of fluorine containing system, solid phase precipitation was not observed in the interlayer. The results of CaO dissolution experiments indicated these interlayers also affected the dissolution rates. The CaO dissolution was retarded with the CaO-SiO2-MgO system, compared to the other two kinds of systems. It could be explained by the magnesia precipitation in the interlayer.
  • Fracture Mechanics Investigation of MgO-C Bricks for Steelmaking by Bending and Fatigue Failure Tests Along with X-Ray CT Scan Observation

    pp. 1371-1379

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    DOI:10.2355/tetsutohagane.100.1371

    Fatigue failure tests were firstly carried out. The material constant derived from S-N curve was evaluated and compared with previous study. The compliance method was subsequently used to evaluate the fracture toughness of MgO-C brick and the relationship between the stress factor and crack growth rate. In order to use this method, the effects of brick carbon content on the crack growth rate and crack growth rate in high temperature were investigated.
    As a result, it was found that the crack growth rate increased when the carbon content in brick decreased. This result was confirmed by X-ray CT scans, which revealed large cracks in bricks with a lower carbon content, even in the middle of fatigue failure tests.
    Furthermore, the material constants obtained from fatigue failure test and K-V diagram were compared. A material constant was derived by evaluating the relationship between the crack growth rate and stress intensity factor, and the result was found to agree with the value derived from fatigue failure tests. This result confirms that that material constant derived from fatigue failure tests is the inherent property of the material and corresponds to the variation of crack growth rate with changes in stress factor. The effects of carbon content in MgO-C brick on the crack growth behaviour and fatigue failure mechanism were also investigated.
  • Development of Concave and Convex Defects Inspection on Steel Sheets by Magnetic Flux Leakage Testing Method

    pp. 1380-1385

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    DOI:10.2355/tetsutohagane.100.1380

    Concave and convex defects on steel sheets cause problems in the steel production line. These defects are usually invisible since their height or depth is as small as the normal surface roughness of steel sheets. Therefore, they can only be detected by human inspection after grinding the steel surface with a grindstone.
    We found that Magnetic Flux Leakage Testing (MFLT) is effective for detecting these kinds of defects. The MFLT method can detect not only magnetic flux caused by the shape of defects, but also that caused by the strain of defects. This paper describes the results of experiments to verify the principle of the detection method and in-line experiments. As a result of the in-line experiments, it was found that some defects cause MFLT signals which are too small to detect automatically. To solve this problem, we proposed a new periodical method to improve detectability. Based on these results, we developed an in-line concave and convex defect inspection technique.
  • Quantitative Analysis of Free-lime in Slag by X-ray Diffraction Method

    pp. 1386-1390

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    DOI:10.2355/tetsutohagane.100.1386

    [in Japanese]
  • Effect of Annealing on the Structure and Hardness of Electrodeposited Ni-W Alloys

    pp. 1391-1397

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    DOI:10.2355/tetsutohagane.100.1391

    Electrodeposition of Ni-W alloys was conducted from an unagitated sulfate solution containing citric acid at pH 5 and 60 ºC under coulostatic (3.44×105–6.22×105 C/m2) and galvanostatic (30-5000 A/m2) conditions. Before annealing, the lattice constant of Ni increased linearly with an increase in the W content up to 40.7 mass% in accordance with Vegard’s law, showing the W supersaturated solid solution into Ni. At W contents of < 37.1 mass%, the deposits showed a morphology of field oriented texture, which a preferred orientation of specific plane occurs toward the electric field in deposition, and the edges of platelet crystals were exposed at surface. At W contents of > 40.7 mass% of solid solubility limit, the cross section of deposits showed a layered morphology, while the surface became smooth with small granular crystals. After annealing, Ni4W precipitated in deposits of W contents of 32.6 and 37.1 mass%, while both Ni4W and NiW precipitated entire surface finely in deposits of W contents of 40.7 to 45.3 mass%. Before annealing, the hardness of deposits increased with W content, and the increase was particularly large at W content of 40.7 mass%. The hardness was almost constant regardless of current density at W contents of > 40.7 mass%. The alloy composition to change the hardness of deposits significantly corresponded with that to change the structure of deposits. The hardness of deposits increased at all W contents by annealing, and the degree of increase was particularly large at W contents of > 40.7 mass%.
  • Development of Aluminide Coated Steels with Gradually Changed Compositions by Lamination Cladding and 2step Heat Treatment

    pp. 1398-1407

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    DOI:10.2355/tetsutohagane.100.1398

    Aluminide coating layers with gradually changed compositions and microstructures on pure Fe plate substrates were developed by the process combining lamination cladding with 2step heat Treatment. The first heat treatment at 933 K for 1.8 ks was applied to initially form the coating layer consisting of Fe2Al5 by the reaction diffusion between the Fe substrate and the melted Al. The second heat treatments at temperatures ranging from 1173 K to 1473 K were subsequently applied to promote the gradual changes in the aluminum compositions and the microstructures, leading the diffusion reaction between the Fe substrate and the initial layer of Fe2Al5. By heating at 1173 K and 1273 K, the initial coating layers of Fe2Al5 exhibited gradual changes in microstructures, leading the formation of layers consisting of Fe2Al5, FeAl2, FeAl, α-Fe with Al. On the contrary, by heating at 1373 K for 180 s, the constituent phases of the graded coating layer changed into Fe2Al5, FeAl2, ε phase, FeAl, α-Fe with Al. ε phase existing at elevated temperatures more than about 1373 K changed into the FeAl2+FeAl lamellar structure by the eutectoid reaction during cooling, resulting in the formation of different microstructural morphology compared with those formed at 1173 K and 1273 K. By heating at 1373 K for 300 s, the constituent phases of the graded coating layer changed into ε phase, FeAl, α-Fe with Al, exhibiting the decomposition of Fe2Al5 and FeAl2. By heating at 1373 K for 3.6 ks, the dominant phases of the coating layer were found to be FeAl and α-Fe with Al, indicating low aluminum compositions below 50at%.
  • Influence of Intergranular Bainite and Intragranular Bainite on Hardness of High Chromium Cast Steel

    pp. 1408-1412

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    DOI:10.2355/tetsutohagane.100.1408

    Effects of quenching rate from austenite temperature on microstructures in the high chromium cast steel containing 1.6%C, 0.6%Si, 0.7%Mn, 0.5%Ni, 12%Cr and 1.5%Mo were investigated. The specimens were destabilized at 1000 ºC for 7.2 ks and then cooled to room temperature at quenching rates ranging from 50 to 0.05 ºC/s. Detailed analysis of temperature-dilatation diagrams with referring to microstructural observations on the specimens etched using LePera etchant lead to define a very narrow bainite region in a CCT diagram. Bainite was formed along grain boundaries when the specimen was quenched at 0.2 to 1.0 ºC/s. The temperature range for bainite transformation was about from 230 ºC to 260 ºC. Grain boundary bainite showed little effect on hardness of the specimen.
    Hardness and microstructures were also investigated on the specimens quenched at 0.2 ºC/s to 400 ºC followed by quenching at various cooling rates to room temperature and tempering at 550 ºC for 1.8 ks, in order to optimize heat treatment conditions for large practical products. Hardness of the specimen quenched at 0.006 ºC/s in the second stage quenching was increased with tempering. The increase in hardness was interpreted as a result of enrichment of carbon content in austenite due to formation of grain boundary bainite, that is, retained austenite containing high carbon content transformed into martensite with tempering.
  • Precipitation Behavior and Inhibition Effect of MnS, MnSe and AlN in 3% Si Steel

    pp. 1413-1420

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    DOI:10.2355/tetsutohagane.100.1413

    The precipitation behavior of MnS, MnSe and AlN in 3% Si steel was investigated for understanding inhibition of grain growth under isothermal annealing. It became clear that the precipitation of AlN was greatly influenced by that of MnSe. The precipitates became fine when hot-rolled at low temperature, and therefore the grain size after the recrystallization annealing became small. Similarly, the grain size after the isothermal annealing became small when the precipitates became fine. When MnS or MnSe precipitates formed complex with AlN, Ostwald ripening was suppressed, as a result, grain growth was inhibited.
  • Effect of Manganese Content on Burring in 0.2%C-TRIP Sheet Steels with Polygonal Ferrite Matrix

    pp. 1421-1425

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    DOI:10.2355/tetsutohagane.100.1421

    Effect of manganese content on burring and tapping in 0.2C-1.5Si-(1.0-2.0)Mn (mass%) high strength TRIP-aided sheet steels with polygonal ferrite matrix (TDP steels) was investigated for automotive applications. Burring test was performed on a machining center with rotational speed of 3500 rpm and cutting feed rate of 10 mm/min, using disc specimen of 50 mm in diameter. Moreover, tapping test was performed on a machining center with rotational speed of 20 rpm and cutting feed rate of 20 mm/min after burring. The hardness of flange after burring was evaluated by hardness increment (ΔHV) expressed by ΔHV=HVmaxHV0, where HVmax and HV0 are a maximum hardness after deformation and a base material hardness (an initial Vickers hardness).
    The hardness increment (ΔHV) increased with increasing of manganese content. The lower the initial carbon concentration in retained austenite (Cγ0), the higher the hardness increment (ΔHV). Strain induced transformation and work hardening contributed to the toughness of flange after burring with TDP steel having a tensile strength of 980 MPa grade.
  • A Field Experiment of Sulfide Reduction in Silty Sediment using Steelmaking Slag

    pp. 1426-1432

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    DOI:10.2355/tetsutohagane.100.1426

    Hydrogen sulfide is generated through sulfate reduction under anaerobic condition in enclosed coastal seas. It is highly toxic, depletes oxygen and generates blue tide. To evaluate the sulfide reduction effect of steelmaking slag, we carried out field experiments in Fukuyama inner harbor, where the people there have suffered from odor caused by gasses including hydrogen sulfide generated from the sediments. We placed the steelmaking slag on the sediments, and monitored the water quality of interstitial water in the sediments and the overlying water of the sediments as well. Hydrogen sulfide gas was also collected and measured.
    The results showed that dissolved sulfide concentrations in interstitial water in the control plots ranged from 100 to 350 mgS/L, on the other hand, those in the steelmaking slag construction area were suppressed, being below 5 mgS/L. The reduction effect of dissolved sulfide by steelmaking slag has lasted for about two years. It was supposed that Fe ions eluted from steelmaking slag may have reacted with sulfide. Species number and individual numbers of macro benthos increased in the experimental area.
    The results imply that capping the deteriorated sediments with steelmaking slag can effectively improve the water and sediment quality of coastal areas.

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