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

Tetsu-to-Hagané Vol. 68 (1982), No. 13

  • Energy-use Changes of Japan's Steel Industry

    pp. 1675-1685

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  • On Ferrous Scrap Recycling

    pp. 1686-1693

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  • Diffusivities in Molten Slag, Molten Iron, Steel and Refractories

    pp. 1694-1705

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  • Recent Trends of Steelmaking Refractories

    pp. 1706-1712

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  • Structure of Steel Studied by the Mössbauer Effect

    pp. 1713-1718

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  • Condensing Phenomenon of Moisture in Sintering Bed and Its Effect on Bed Permeability

    pp. 1719-1727

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    Condensing phenomenon of moisture in sintering bed and its effect on sintering process were quantitatively studied through a mathematical model and experiments with sintering pot. The results obtained are as follows:
    (1) Remarkable reduction of bed permeability after ignition is mainly due to formation of moisture condensation zone in bed. Resistance to gas permeation in moisture condensation zone is higher than that in initial raw mixture zone.
    (2) The amount of condensed moisture is determined by the difference between wet-bulb temperature of gas passing through the bed and temperature of raw mixture. The less the difference is, the less the amount of condensed moisture is.
    (3) As the amount of condensed moisture reaches a critical level at which sticking force of fine grains in quasi-particles starts to decrease, quasi-particles begin to agglomerate. Thus voidage of bed decreases and resistance to gas permeation increases sharply.
    (4) It is proposed that effective means for suppressing moisture condensation after ignition are increase of raw mixture temperature, reduction of humidity in gas passing through bed, addition of moisture-absorber to bed and granulation of raw mixture at lower moisture content, etc.
    x

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  • Activities of Sulphur and Oxygen in Liquid Iron

    pp. 1728-1736

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    The equilibria of reactions between liquid iron and H2S-H2O-H2-Ar gas mixture were examined using a resistance furnace in order to make clear the interaction between sulphur and oxygen in liquid iron. The gas mixture was sufficiently preheated by adjusting its total flow rate, and hence thermal diffusion was avoided. Soundly solidified specimens were obtained when the gas mixture was diluted with argon. How-ever, adding too much of argon and water vapor decreased the values of PH2S/PH2 thermodynamically calculated. Therefore, experiments were performed on the basis of the condition, under which H2S-H2-Ar gas mixture was in thermal equilibrium.
    As a fundamental study, measurements were carried out for liquid iron equilibrated with H2S-H2 and H2O-H2 gas mixtures using the same resistance furnace.
    The interaction parameters eO(S) and eS(O) at 1 500, 1 550 and 1 600°C were obtained by combining the results for Fe-O-S system with those obtained in the present study for both Fe-O and Fe-S systems.
  • Characteristics of Dephosphorization in a Bottom Blown Converter and Its Application to the Preliminary Treatment of Hot Metal

    pp. 1737-1743

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    Dephosphorization during blowing in a 5 ton bottom blown converter has been studied. The effects of lime size and injection pattern on dephosphorization have also been investigated in a 230 ton Q-BOP. The phosphorus partition suitable for the bottom blown converter has been obtained by the regression analysis of experimental data.
    Injection of lime and premelt powder mixtures into the 5 t test Q-BOP has revealed that dephosphorization proceeds largely in the early stage of blowing. This characteristic has been utilized to develop a new and effective dephosphorization pretreatment of hot metal in Q-BOP. This new technique has enabled us to dephosphorize hot metal from ca. 0.14% to 0.010%P with a consumption of 20 kg CaO/tpig and 3 kg CaF2/t-pig within 2 to 4 minutes of oxygen blowing. The ultra-low phosphorus and sulfur steels have been successfully produced by the newly developed technique.
  • Mechanism of Hot Metal Dephosphorization by Injecting Lime Base Fluxes into Bottom Blown Converter

    pp. 1744-1753

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    Hot metal dephosphorization in Q-BOP was shown in the previous work to be very quick and efficient. Experiments have been made to determine the contribution to the dephosphorization of top slag (permanent reactor reaction) and of lime powders injected from bottom tuyeres with O2 gas and ascending in the bath(transitory reaction).
    The ratio of dephosphorization, 100 {[P]initial-[P]final}/[P]initialreached 90-95% when fluorspar is added either to injected lime or to resulting top slag, whereas it decreased to 50-70% without the fluorspar addition. Detailed analysis has shown that 50-70% of the above ratio of dephosphorization is shared by the transitory reaction, the rest of 0% (without fluorspar) to 25-40% (with fluorspar) by the permanent reactor reaction. Slag particles ascending in the bath have been sampled and found to contain 10- 30%P2O5, confirming the considerable contribution of the transitory reaction.
    With the aid of additional laboratory experiments, the following sequence is found operative for the dephosphorization: Lime particle injected with O2 gas is transformed to calcium ferrite. During ascending in the bath, calcium ferrite oxidizes [P] to P2O5, itself being reduced to CaO which combines with P2O5 to form 3CaO -P2O5 particles.
  • Formation of Silica Inclusions during the Cooling and Solidification of Fe-Si-O Alloys

    pp. 1754-1763

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    Fe-Si-O alloy melt kept at 1 600°C or 1 645°C in silica crucible for 20 min was cooled to 1 555°C, and then heated again to the initial temperatures and kept for 20 min. Such cooling and heating cycle was repeated several times. Specimens were taken from the melt at 1 600°C and 1 555°C during each cooling period. Silica inclusions in the specimens generally consisted of three groups of different sizes; the smaller particles of 0.5 μ diam. delineated the cellular structure of the specimen, the medium ones of roughly 4 μ appeared inside of the cell, and the larger ones of 620 μ were randomly distributed. The number, size and form of particles of each size changed significantly with the silicon content of the melt, the sampler used and the repeated number of the cycle. It was concluded that the larger particles were formed during cooling of the melt and the medium and smaller ones precipitated during solidification of the specimen. The numbers of the larger sized particles in the specimens taken at 1 600°C and 1 555°C during each cooling period from 1 645°C agreed well with each other.
  • The Metallographical Characteristics and the Formation Mechanism of Longitudinal Surface Cracks in CC Slabs

    pp. 1764-1772

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    A plant experiment was carried out the copper mould of a continuous slab caster was artificially grooved and thus longitudinal mid-face cracks were formed. The obtained cast samples were metallographically examined. Local segregation of C, Mn, P and S existed in front of longitudinal cracks in both directions of thickness and length and the cracks propagated along these segregated regions. This feature was common in cracks appeared differently.
    The very vicinity to the crack entry showed the deformation of ferrite and pearlite structure. This means that the opening of cracks to the surface occurred when the surface temperature decreased below Ar3 point, possibly in the secondary cooling zone.
    A formation mechanism of longitudinal surface cracks was proposed based on these findings.
  • Effect of Irregularity in Solidified Shell Thickness on Longitudinal Surface Cracks in CC Slabs

    pp. 1773-1781

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    The source of longitudinal mid-face cracks was investigated and found to be the local retardation o solidification at the early stages.
    The crack occurrence tendency was very sensitive to the size of surface groove at the meniscus of mould, the property of mould flux and steel composition. This local retardation of solidification did not diminish during travelling in the mould.
    It was possible to evaluate casting conditions by estimating the uniformity of solidified shell thickness and surface temperature by the temperature measurement of copper mould.
    x

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  • Mathematical Model Analysis on the Formation Mechanism of Longitudinal, Surface Cracks in Continuously Cast Slabs

    pp. 1782-1791

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    Stress and strain in freely shrinking shell within a CC mould were calculated. The maximum tensile strain was resulted in a 0.14%C steel in the brittle temperature range near the melting point when the peritectic reaction below a quasi-solidus temperature (Ta) was considered as well as the Ar4 transformation above Ta-30°C. Stress and strain localization to a thinner shell in the mould was analyzed. Stress and strain in the shell at the beginning of a secondary cooling zone were also calculated. Finally, formation of the thinner shell was mathematically modeled from the view point of thermally induced shell deflection.
    By the use of the results above, effects of carbon contents, flaw size in mould surface, and secondary cooling on longitudinal surface cracking and crack depth in continuously cast slabs were discussed, and then the experimental result and experience in the continuous casting operation were explained.
  • ロボットの出荷割合比率/我が国製鉄所の分布/製造業の省エネルギー設備投資比率/ハンプティー・ダンプティー/世界の鉄鉱石生産高/鉄鋼業における研究開発費の推移

    pp. 1791-1791,1829

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  • Improvement of Longitudinal Surface Cracks in CC Slabs by Air-water Mist Cooling Method

    pp. 1792-1798

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    In order to prevent longitudinal surface cracks, a new type of air atomizing nozzle has been developed and applied to continuous casting machines as a secondary cooling system.
    1) Air atomizing nozzle is superior to conventional spray nozzle in uniformity of slab surface temperature, in performance reliability and in wider applicability of cooling density.
    2) Longitudinal surface cracks are remarkably reduced by this mist cooling method.
  • Ununiform Deformation of 18% and 25% Chromium Steel on Hot Extrusion

    pp. 1799-1807

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    Mechanism of stringy defect formation on hot extrusion of high chromium steels and its prevention methods were investigated.
    It was estimated that stringy defect resulted from the strain in circumferential direction relatively larger than in extrusion direction.
    Stringy defect can be prevented by refining the structure, i.e. promoting the precipitation of austenite or adding a carbide/nitride former element.
  • Growth Kinetics of Intermediate Phases in Hot Dip Galvanizing

    pp. 1808-1812

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    The previous experimental results on the formation and growth kinetics of intermediate phases in reaction between solid iron and solid or liquid zinc at various temperatures have been investigated in more details. In a function of temperature T(K) and time t(min) A(T, t) = T (logt +16.7), beginning times of characteristic formation and growth processes of the intermediate phases are constant irrespective of reaction temperature and whether zinc is solid or liquid. Irrespective of temperature and zinc state, phase growth curves using A (T, t) instead of t represent the almost similar shapes which change with occurences of the above characteristic processes. The relation W = ktn shown in many previous papers has roughly been obtained in this study, where W is thickness of intermediate phases and t is reaction time in hot dip galvanizing. Difference in values of the exponent n among investigators seems to be due to differences in their experimental temperatures and times. Since the phase growth curves do not correctly obey the relation W = ktn using a single n value, rate determining process in hot dip galvanizing reaction should be discussed from another standpoints.
  • Effect of the Nature of Grain Boundaries on the Creep Rupture Properties of a Nickel-base Superalloy in Hot Corrosive Environment

    pp. 1813-1822

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    The creep rupture tests of a nickel-base superalloy Inconel 751 were carried out at 800°C in static air for the specimens which were variously heat-treated and coated with synthetic ash mixture composed of 90% Na2SO4 plus 10% NaCl and the effect of the nature of grain boundaries on the creep rupture properties was investigated. In directly aged (DA) specimens which had zigzag boundaries with coarse titanium-rich carbides, a drop in the rupture strength due to hot corrosion was less pronounced than that in simply aged (SA) and triple heat treated (THT) specimens which had straight boundaries with chromium-rich carbides. The rupture ductility, however, lowered remarkably as a result of brittle fracture mode due to hot corrosion regardless of the nature of grain boundaries.
    From the metallographic examination, it was clarified that the rupture life of Inconel 751 subjected to hot corrosion was chiefly determined by the behavior of aggressive intergranular penetration of sulfides, which depended strongly upon the grain boundary configuration and the boundary carbide constituents. It was also suggested that the zigzag boundaries and the existence of coarse titanium-rich boundary carbides would control the intergranular penetrations to obey a given kinetics by virtue of their beneficial effect on preventing both stress activation and chromium-depletion at grain boundaries, and therefore a decrease in the rupture life of DA specimen should be restrained appreciably as compared with SA and THT specimens.
  • High Toughness Steel Heavy Plate with Minimum Proof Stress of 900 MPa for Deep Submergible Vehicles

    pp. 1823-1829

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    A steel intended for use as the hull materials of deep submergible vehicles has been developed. The aimed properties of the steel were minimum proof stress of 900 MPa and high toughness.
    The primary research was conducted on several steels containing nickel of a range from 2.5 to 5 percent with the emphasis on mechanical properties, heat treating characteristics and weldability. The optimum chemical composition of steel having the above-mentioned properties has been determined as 0.09C-5Ni-0.5Cr-0.5Mo-0.05 V with minimal impurities, especially, low sulfur content. Production heats of this steel were made. Electroslag remelting process was applied to make slabs of ultra low impurities and super cleanliness. Quenched and tempered steel plates of 65 mm thick exhibited proof stresses ranging from 931 to 960 MPa, and V-notch charpy shelf energy ranging from 172 to 209 J.
    This steel plate was applied for the hull material of deep submergible vehicle ("Shinkai 2 000") operating in seas of 2 000 meters depth.
  • Evaluation of Brittle Fracture Strength of Surface Notched Round Bar

    pp. 1830-1838

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    The brittle fracture strength of surface notched round bar (SNRB) has been investigated theoretically and experimentally. Firstly, the stress intensity factors for SNRB subjected to axial load and bending, KA and KB, respectively, have been analyzed with the aid of the finite element method. Secondly, the brittle fracture test under axial load has been conducted on SMn443 and SCM440 specified in, JIS. The curve showing the relationship between net section stress at fracture, σn, F, and testing temperature. T, covers two regions macroscopically. One is called Region I where σn, F, diminishes with decreasing T, and the other is Region II, where σn, F, is nearly constant irrespectively of T. The effect of diameter, D, and notch depth, α, on σn, F in Region I can be evaluated on the basis of linear elastic fracture mechanics technology. σn, F in Region II shows little change with D, and diminishes with an increase in relative notch depth, α/D. σn, F in Region II can be approximately estimated on the basis of semi-experimental equation derived from general yielding stress level of SNRB. Lastly, the fracture test under combined load of tension and bending has been conducted on PMMA. The fracture stress under combined load can be estimated from the following criterion, KA+KB=KC where KC. is fracture toughness.
  • Measurement of Dynamic Fracture Toughness, JId, by Instrumented Charpy Test

    pp. 1839-1841

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  • 最近の欧米鉄鋼業の研究所をめぐりて

    pp. 1848-1849

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  • 抄録

    pp. 1861-1864

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