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

Tetsu-to-Hagané Vol. 84 (1998), No. 1

  • Wetting Phenomena in Materials Processing

    pp. 1-6

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    It is well known the wettabilities of liquids by solids play an important role in materials manufacturing including iron and steel making. Non-wetting systems are required in some cases such as deoxidation process in steel making and wetting ones are sometimes desired to fabricate high quality metal matrix composites. In this meaning it is necessary to control the wettability to produce high quality materials. In this paper, factors affecting the wettability are described and how the wetting phenomena affect in materials manufacturing process, especially in deoxidation process and solidification process of steel are reviewed.
  • Estimation of Hamaker Constants of Al2O3/Al2O3, Al2O3/Bubble in Molten Iron Using Fowkes's Method

    pp. 7-12

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    The Hamaker constants of molten iron and Al2O3/Al2O3 and Al2O3/bubble in molten iron at 1600°C (AFe, AAFA, AAFB) were estimated using Fowkes's method from the wettabilities and the Hamaker constant of Al2O3 at room temperature and the values obtained were as follows respectively :
    AFe=10.5×10-19J
    AAFA=3.98×10-19J
    AAFB=6.47×10-19J
    Then, coagulation coefficient of Al2O3 inclusions in turbulent molten steel and the separation rate of inclusions caused by the interaction with bubbles were estimated through using the Hamaker constants obtained to the theories reported by other researchers.
  • Separation Mechanism of Inclusion from Molten Steel during RH Treatment

    pp. 13-18

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    Behavior of Al2O3 inclusion particles in molten steel was researched after deoxidation in RH degasser and ladle refining furnace (NK-AP).
    Diameter distribution of inclusion particles was measured by photo scattering method. In result, it was observed that inclusion particles were almost Al2O3 spheres and logarithm of number of inclusion particles were directly proportional to diameter of inclusion particles in Al-killed molten steel.
    It was observed that removal rate of bigger inclusion particles were faster than that of smaller inclusion particles, and particles under 3μm were hard to be removed.
    Because it was cleared that inclusion particles weren't removed by floating of mono-particles, model considered turbulent coagulation of inclusion particles in stirring molten steel was constructed by Saffman-Turner model and mass balance of inclusion particles.
    In result, behavior of inclusion particles in molten steel was explained in both of RH degasser and NK-AP by this model.
  • Nonequilibrium Wetting in Si/Al-Si and Ni/Al-Ni Systems

    pp. 19-24

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    Wetting phenomena have been investigated for a long time. The investigation of the wetting phenomena originated from the field of adhesion and waterproof treatment, but the chemical reaction or the mass transfer between liquid and solid have not been considered. In this paper, the influence of the reaction and the mass transfer on wetting were studied.
    During the contact angle measurement of metal/metal and ceramics/metal systems at high temperature, we have to take care with interfacial reactions and mass transfer at the interface. The influence of the interfacial reactions and the mass transfer is microscopically inspected on the interface between solid and liquid after the contact angle measurement.
  • The Wettabilities of Graphite by Liquid Carbon-saturated Fe-Cu, Fe-Sn and Fe-S Alloys

    pp. 25-30

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    The wettabilities of carbon-saturated Fe-Cu, Fe-Sn and Fe-S melts to graphite were measured by the sessile drop method. The works of adhesion of those alloys with graphite are dependent upon the solubility of carbon in those alloys. With an increase in the content of the above alloying elements in liquid alloys, the solubility of carbon and the work of adhesion decrease. This is why the surface-active elements, Cu, Sn and S, are considered to segregate at the interface between the liquid alloys and the graphite as well as at the surface of the liquid alloys. Those segregation phenomena may interfere the wettability of the liquid alloys to the graphite.
  • Relationship between Region of Preferential Vaporization and Bath Convection in Ar Arc Plasma Melting

    pp. 31-36

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    In Ar arc plasma melting of metal button, metal vapor mainly generates at outer region of anode spot. To make clear the relationship between the vaporization and the convection flow in bath, spectroscopic measurements were performed for determining the space distribution of vapor pressure of metal. Then the convection flow in bath was determined by motion of Y2O3 particles added to bath surface and EPMA analysis of cross sectional area.
    There were two flows with different direction of motion in bath. They collided at about 7mm from central axis that is at the same position of maximum vapor pressure. Y2O3 particles were observed in the periphery owing to the outward flow. In the center of bath, it is considered that the inward flow is driven by electro-magnetic force. This flow carried the melt with high Ar content to the vaporization spot, and then an enhanced vaporization was operated due to transition of the Ar in melt to gas phase.
  • Development of Injection Lance with High Combustibility for High Rate Coal Injection

    pp. 37-42

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    To attain a high rate injection of pulverized coal into a blast furnace, it is required to increase a combustion efficiency of pulverized coal in the raceway. Therefore, it is important to design the injection lance with high combustibility based on the essential understanding of combustion behavior of pulverized coal.
    Previous to the start up of the high rate injection operation at Fukuyama No.4 BF, a 2-dimensional mathematical model of pulverized coal combustion taking the lance arrangements and the dispersion of coal particles into account had been newly developed. As a result of the analysis using this model, it was found that the eccentric double lance, two lances arranged asymmetrically to avoid the interactions of the pulverized coal flows, had superior characteristics to increase the combustibility in the blowpipe and the raceway due to the intensified particle dispersion. Since the experiment using hot model also showed the same effectiveness, the eccentric double lance was adopted to all tuyeres of Fukuyama No.4 BF.
    During the high rate injection operation in October 1994, pulverized coal rate was raised to 230 kg/t and little unburnt char was detected in the top waste dusts and the combustion efficiency of pulverized coal estimated by the sampled char from deadman during scheduled shut down just after the operation reached over 70%. These results suggests that the high combustion efficiency had been successfully achieved by using the eccentric double lance.
  • The Formation Mechanism of Center-line Cracking on the Continuous Cast Slab

    pp. 43-48

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    Continuously cast slab may contain linear cracks in the middle of the slab thickness.This crack is called the centerline cracking.In many cases, the cavity cannot be closed through the rolling process and presents itself as a defect.
    In this paper, the formation mechanism of center-line cracking has been discussed on the bases on investigation of center-line cracking and analysis of relevant operating conditions.
    The results are summarized as follows,
    (1) Center-line cracking is a shrinkage cavity created through the solidification of molten steel closed off in the vicinityof final stage of liquid core.
    (2) The enclosed liquid thickness calculated from the cavity data is about 6mm.
    (3) The defect intervals of slabs coincide with the circumference of the roll in the neighborhoodof the unbending point.
    (4) Center-line cracking is apt to occur when the slab is cast in the crack-sensitive range.
  • Estimation of Primary Dendrite Arm Spacing and Solidified Interface Morphology in Low Carbon Steel by Introducing Quasi Fe-C Binary Alloy

    pp. 49-54

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    In order to characterize the solidified structure of low carbon steel, uni-directional solidification experiments have been performed using various commercial grade low carbon steels. Conditions of uni-directional solidification experiment carried out in this study are followings : Temperature gradient : 3.4·103K/m, Growth velocity : 1.67·10-5m/s and 8.33·10-5m/s.
    The solid/liquid interfacial morphologies (cellular or dendritic) have been observed on longitudinal and horizontal cross section of the specimens. The primary dendrite arm spacing ( or inter cellular spacing), λ1, has been measured on the horizontal cross section. These experimental data have been compared with theoretical model, which is based on the marginal stability criteria.
    It has been found that it is impossible to describe the solid/liquid interfacial morphology and λ1 using carbon content in steel when carbon content is low (e.g. C0 < 0.1mass%). Equivalent carbon content (C0') for description of solidified structure is newly defined as follows:
    C0'=1.066(%C)-0.202(%C)2+0.019(%Si)+0.0043(%Mn)+1.1775(%P)+1.6740(%S)
    The solidification range in quasi Fe-C binary system at C0' equates with that in real steel. Using C0' it is possible to characterize solid/liquid interfacial morphology and size in solidification of commercial grade steel when carbon content is less than 0.1mass%.
  • The Measurement of Ar Solubility in Water by Using Spectrometer

    pp. 55-60

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    To measure the solubility of Ar in liquid, a modified gas probe has been developed, which consists of the injection of He gas into liquid through a nozzle, the collection of assembling bubbles of He-Ar gas mixture and the determination of concentration of Ar in the He-Ar gas mixture using a high sensitive mass spectrometer. To examine the reliability of this method, the measurement of Ar solubility in water was carried out and the effects of experimental conditions with solubility were examined.
    Under the established experimental condition, the obtained solubility has a reasonable agreement with previously reported values and it was represented by ln[Ar]=-8.98+1645.5/T
  • Relative Sensitivity Factors for Cu, Al, and Ti-based Metals in Glow Discharge Mass Spectrometry

    pp. 61-66

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    Relative sensitivity factors ( RSFs ) in the analysis of glow discharge mass spectrometry were determined for Cu, Al and Ti-based metals. Pin-shaped and disk-shaped samples for the respective matrices were prepared from the same blocks. A systematic deviation has been recognized between the values of RSFs for pin-shaped samples and disk-shaped samples in all the matrices. The manner of the deviation is quite similar to that in Fe and Ni-based metals as has already been reported and the deviation in each matrix is expressed by a linear relation. RSFs for disk-shaped samples are obtainable from those for pin-shaped samples by the linear relation and vice versa.
  • Graphite Nucleation on Boron Nitride in 0.53% C Steel

    pp. 67-72

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    The effects of boron, aluminium, and rare earth metals (REM) on the graphitization at 700°C in 0.53% C steel were investigated in order to clarify a mechanism of graphite nucleation on the precipitates using a field emission transmission electron microscopy.
    The graphitization is promoted by the addition of boron, aluminium, and REM, since the precipitates such as BN, AlN, and REM-sulfide play the role as nucleation sites of graphite.BN increases the number of graphite particles and shortens the time required for the completion of graphitization more effectively than AlN and REM-sulfides.
    BN in steel consists of several single crystals whose [000 2] axes radiate from the center of particles to the surface.Therefore, BN particle exposes its basal plane of (0001).The (0001) planes of a graphite particle epitaxially nucleate on each (0001) plane of BN, and each [0001] axis of graphite also radially grows to the surface.
    BN and graphite have a similar crystal structure to each other, and the morphologies are also very similar.It seems that the graphite particles easily nucleate and grow epitaxially on the surface of BN.
  • Microstructure at Interface of Steel/Aluminum Bonding Sheet and Formation of Intermetallic Compound

    pp. 73-78

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    This paper deals with the relation between the microstructure and the formation of intermetallic compound (IMC) at the interfaces of the bonding sheets. The bonding sheets, steel/aluminum alloy (CS/As) and stainless steel/pure aluminum (SS/A1), were produced by hot rolling. From the results of TEM observation, it was found that aluminum or chromium oxide films were existed and the IMC were formed locally at the interfaces of the bonding sheets. Two or three types of the IMC composed of columnar structure were formed at the interfaces of the bonding sheets after heating. The oxide films remained at the IMC/aluminum interfaces of the CS/A5 bonding sheets. The specific crystallographic orientation relationship was recognized at the SS/IMC interfaces of the SS/A1 bonding sheets. It was considered that the formation of the IMC were greatly effected by the oxide films existed at the interfaces of the bonding sheets.
  • Effect of Primary Carbide on Fatigue Life in Die Steel for Cold Working

    pp. 79-84

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    The life of dies for cold working was markedly decreased by increasing stress applied to the edge of die; because the strength of materials for works was increased. It was found from an investigation of fractured waste dies which were used at high stress that fracture of dies originated at coarse primary rod-like carbides. It was confirmed that fatigue life of dies used at high stress could be evaluated with tension-compression fatigue test whose frequency was equivalent to that of practical dies. The effect of primary carbide on the fatigue life of JIS SKD11 die steels was studied on the basis of tension-compression fatigue test results. The fatigue life, N, at stress of 1.65GPa which is similar to stress applied to the edge of die decreased with an increase in the maximum width, W, of primary carbide following the equation : N=103.12-0.08W. Voids already initiated at interfaces between coarse primary carbides and matrix at extream low stress (plastic strain) of 0.3GPa (0.001%) in tensile tests.
    Voids were generated at all of coarse carbides more than 8μm of width and seldom at carbides less than 2μm. Thus, it is important that coarse primary carbides corresponding to latent crack are reduced to life of dies for cold working.

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