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

Tetsu-to-Hagané Vol. 70 (1984), No. 2

  • Latest Bonding Processes of Heat Resisting Alloys

    pp. 151-157

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  • Application of Modern Electron Microscopy to Ferrous Materials

    pp. 158-165

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  • ブルーム連鋳々片の断面扁平比の推移

    pp. 165-165

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  • Vibration-damping Materials

    pp. 166-170

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  • Recent Progress of Bonding Technology

    pp. 171-177

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  • Analysis of Permeability and Characteristic Suction Gas Volume in Sintering Process

    pp. 178-185

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    Permeability experiments have been performed for each characteristic zones (moisture condensation, drying, reaction, melting and cake zone).
    The analysis of reaction zone is satisfactorily made by combination of static experimental test and mathematical dynamic model in sintering process.
    By this model including pressure drop equation of each zones, calculations are made simultaneously for the variation of heat transfer, moisture transfer, reactions of coke and limestone, melt of solid and suction gas volume rate.
    It is concluded that the total gas volume is determined by the ratio of the specific heat of material to that of suction gas, independing on suction pressure or bed height.
  • Phosphorus Distribution between MgO-saturated CaO-FetO-SiO2-P2O5-MnO Slags and Liquid Iron

    pp. 186-193

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    The phosphorus distribution ratios between CaO-MgOsat.-FetO-SiO2-P2O5(≤3 wt%)-MnO (25 wt%) or CaO-MgOsat.-FetO-SiO2-P2O5 (45 wt%) slags and liquid iron have been obtained in the temperature range from 1 550 to 1 650°C, The dephosphorization quotients can be expressed by the following three different equations.
    i) log (P2O5)/([P]2(FetO)5)=0.145[(%CaO)+0.3(%MgO)-0.5(%P2O5)+0.6(%MnO)]+22 810/T-20.506
    ii) log (P2O5)/([P]2(FetO)5)=7.87 log [(%CaO)+0.3 (%MgO)-0.05(%FetO)-0.5(%P2O5)+0.6(%MnO)]+22 240/T-27.124
    iii) log (P)/([P](T.Fe)5/2)=0.0720[(%CaO)+0.3(%MgO)+0.6(%P2O5)+0.6(%MnO)]+11 570/T-10.520
    The activity coefficient of P2O5 by TURKDOGAN and PEARSON'S treatment can be expressed as follows :
    logγP2O5=-1.02(23NCaO+17NMgO+8NFetO-26NP2O5+13NMnO)-22 990/T+9.490
    In the plot of logarithms of activity coefficient of FetO against mole fraction of SiO2, the values for log γFetO tend to increase with increasing the P2O5 content.
  • Effect of Electromagnetic Stirring at the Final Stage of Solidification of Continuously Cast Strand

    pp. 194-200

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    It is commonly observed that severe V-channel segregates are associated with the equiaxed zone in the central region of a strand. This type of segregation may deteriorate the product qualities especially for sour gas service. The modification of V-segregates is found to be attained by electromagnetic stirring at the final stage of solidification. The laboratory scale stirring experiments have been carried out in order to eliminate V-segregation and the following results have been obtained.
    1) V-segregation streaks can be eliminated by linear or rotary type stirrer at the final stage of solidification.
    2) The upward flow of molten steel at the solidification front which may prevent the inter-dendritic liquid flow toward the bottom is effective.
    3) In the case of stirring by rotary type stirrer, adequate amount of fine equiaxed crystals is necessary. Alternating stirring at the final stage of solidification may prevent coagulation of equiaxed crystals and modify the packing of them.
    4) It was found that only weak stirring is enough.
    5) It is important to time the stirring to the progress of solidification. Optimum stirring period should be aimed at right after the precipitation of crystals, fraction of solid equals to 0.1 at the center of a strand.
  • Measurements of Roller Forces in Straightening Zones of a Continuous Casting Machine of a Vertical Bending Type

    pp. 201-207

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    Roller forces were measured for the straightening zones (a vertical bending zone and an unbending zone) of a continuous casting machine of a vertical bending type, and the obtained data were analyzed. Further, some numerical calculations were carried out and the measured values of the roller forces were analyzed theoretically.
    The following facts were elucidated :
    (1) Very large roller forces appear when a slab head or a slab tail goes through the unbending zone.
    (2) The roller forces are larger at the exit of the unbending zone than those at the entrance.
    (3) The correlation between roller forces and slab width is not distinct and contrary to usual anticipation, the roller forces are not proportional to slab width.
    (4) The characteristics of the straightening forces in the vertical bending zone are the same as those in the unbending zone.
  • Stress Analysis of Cylindrical Refractory Structures under Restraint of Thermal Expansion

    pp. 208-215

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    An approximate analytical equations were derived to calculate the stress state of cylindrical structure that is constructed by fire-bricks, stamp, joint-mortar and shell.
    In the analysis gradual heating process was assumed, and non elastic behavior was neglected. The main objects are to get the compression field that is made by constraint of thermal expansion, and the tensile stress that is caused by partial compressive loading.
    The analytical solution was compared with that by FEM. The former has little error. This error, however, has no objection to design or to evaluate real furnace.
    Numerical calculation was done to clarify the effect on stress of design parameters of blast furnace hearth refractories, i.e. Young's modulus of fire-brick, that of stamp, length of fire-brick and thermal conductivity, etc..
    x

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  • Metallurgical Aspects of Hot Rolling of Heavy Plates from Continuously-cast Slabs

    pp. 216-223

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    Significance of hot rolling to produce heavy plates from continuously-cast slabs with low carbon and low alloying elements is analyzed from metallurgical point of view, special attention being paid to the influence of solidification structure on the mechanical properties of plates. The major conclusions are as follows ; a) Brittle fracture characteristics (vTrs) is not affected by microsegregation existing in either columnar dendrites or equiaxed grains. b) The appropriate reduction ratio in terms of mechanical properties in the thru-thickness direction is approximately 1.5-3, depending on the rolling shape factor which is a function of slab thickness, radius of rolls, and reduction per pass. c) Some elements such as S, P, Mn, N, and C are detected by an Auger electron microscope on the surface of center porosities which can be annihilated by hot rolling. Based upon the results it is suggested that combination of fine initial austenite grain, large rolling shape factor, and low total reduction ratio is a sufficient condition to procure sound mechanical properties of heavy plates manufactured from continuously-cast slabs.
  • Experimental Study of Piercing Characteristics and Wear of Plugs in Press Roll Piercer of Seamless Pipe

    pp. 224-231

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    Plug life of PRP (Press Roll Piercer) process, in which a square bloom is directly pierced and rolled simultaneously, is strongly affected by its own shape. A plug with a sharp conical top thrusts through the solid material to get galled in the earlier stage by metal flow on its surface. On the other hand, a plug with dull top or a flat top has a longer life, since it is protected by dead metal induced in front.
    As for plug material, conventional tool steel for hot metal forming is durable enough, only if surface scale layer is formed before use. The product quality is also influenced by plug shape. Especially dull one is advantageous.
  • Experimental Determination of γ/(γ+α2)/α2 Phase Boundaries in a Ni-Cr-W-Mo Quaternary System

    pp. 232-237

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    To determine experimentally the solubility of a tungsten-rich bcc α2 phase in a nickel-rich fcc γ phase in a Ni-Cr-W-Mo quaternary system, four Ni-Cr-W-Mo alloys with 0.03wt pct carbon, whose compositions were in a γ+α2 phase field, were equilibrated at 1 000, 1 100, 1 200, and 1 300°C for 8 000, 4 500, 100, and 100h, respectively. Chemical compositions of the constituent phases were determined by means of electron microprobe analysis. Tie-lines between γ and α2 phases and γ/(γ+α2)/α2 phase boundaries were constructed in four isothermal sections of the Ni-Cr-W-Mo quaternary equilibrium phase diagram. The solubility of α2 in γ decreased with decreasing temperatures. Precipitation of carbides such as M6C and M12C at lower temperatures apparently lead to further decrease in the α2 solubility.
  • Transformation to Pearlite from Work-hardened Austenite

    pp. 238-245

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    The effects of austenite deformation conducted below the recrystallization temperature on the subsequent isothermal transformation to pearlite in an eutectoid steel (SKD 6, H11) were quantitatively studied. The plastic deformation in the austenite condition led to marked acceleration of austenite-pearlite transformation. This acceleration was found to be mostly caused by the increase in the nucleation rate but not by the increase in the growth rate.
    The increase in the nucleation rate per unit volume of specimen was attributed (1) to the increase in the austenite grain area by the elongation of grains, (2) to the increase in the nucleation rate per se per unit area of grain surface, and (3) to the formation of additional nucleation sites such as annealing twin boundaries, deformation bands, etc. In this study, the nucleation rate on the grain boundary surface was estimated to be increased about 27 times larger by 30% rolling. The average pearlite fraction nucleated within the grains was found to be 25% of the total transformed fraction.
  • Microstructure and the Mechanical Properties of Dual-phase Steel Produced by Intercritical Annealing of Lath Martensite

    pp. 246-253

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    Microstructure and tensile properties of a dual-phase (martensite + ferrite) Fe-2.3%Mn-0.05%C-0.03%Nb steel produced by intercritical annealing of martensitic specimens have been studied. In order to assess the effects of prior austenite grain size on microstructure and tensile properties of the dual-phase steel, the martensitic specimens with widely different prior austenite grain sizes were prepared by thermal cycling and thermomechanical processing. Coarse dual-phase structure consisting of fibrous martensite and ferrite was obtained by intercritical annealing of the specimens with coarse prior austenite grain size. A characteristic fine dual-phase structure consisting of homogeneously dispersed fine martensite particles and fine ferrite grains was obtained by the intercritical annealing of the specimens with ultra fine prior austenite grain size. The fine dual-phase structure was superior in both strength and ductility to the coarse dual-phase structure over a wide range of martensite volume fractions examined. It is concluded that better combination of strength and ductility of the dual-phase steel is achieved by intercritical annealing of the martensitic specimens with ultra fine prior austenite grain size which is obtained by the thermomechanical processing.
  • Effect of Lowering Si on the Properties of 1Cr-1Mo-V Casting

    pp. 254-261

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    Effect of lowering Si content on the porosity frequency, rupture strength and weldability of Cr-Mo-V large castings for turbine casing and valve was investigated, using large test specimens taken from valve castings having low and high Si content. The results are summarized as follows.
    (1) Deoxidation of low Si cast steel is achieved completely by 0.1% Fe-Ti addition.
    (2) Low Si casting has no inverse V segregation and small amounts of porosity as the results of fine dendrite structure.
    (3) There is no difference, between low Si and conventional Si castings, in hardenability and strength at ambient temperature to 566°C.
    (4) Creep rupture strength is improved by lowering Si content.
    (5) Low Si casting possesses better weldability concerning cold cracking and reheat cracking than conventional Si casting.
  • Influence of Yttrium Addition and Superficial Y2O3 Powder Application to Fe-26Cr-21Ni-1.8Si Alloy on Its High-temperature Oxidation Behavior

    pp. 262-268

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    The isothermal and cyclic oxidation behavior of Fe-26%Cr-21%Ni-1.8%Si alloys with and without superficial Y2O3 powder application as well as similar alloys containing 0.02% and 0.34%Y was examined in air at 1100°C.
    The oxide scales on the surface of yttrium-containing alloys consisted of (Cr, Fe)2O3, and had excellent adherence to the alloy substrate even in cyclic oxidation. No void formation was observed at the alloyoxide interface, and no silicon-rich inner layer was developed. Such effects of yttrium addition were recognized to be significant even in a fairly early stage of oxidation.
    The superficially applied Y2O3 powder on the alloy improved the scale adherence, and provided the oxidation morphology similar to that of the yttrium-containing alloy. The effect of Y2O3 powder was also observed in preoxidized specimens.
  • The Effect of Temper Embrittlement on Hydrogen Embrittlement of 2 1/4Cr-1Mo Steel

    pp. 269-276

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    The effect of temper embrittlement on hydrogen embrittlement was investigated on 2 1/4 Cr-1Mo steel for high-temperature and high-pressure vessels. The threshold stress intensity, KIH, for hydrogen-stress cracking (HSC) was determined by immersing modified 1T-WOL specimens with and without stepcooling heat treatment into a H2S-saturated 0.5% acetic acid solution.
    The results obtained are summarized as follows :
    (1) Temper embrittlement enhances the susceptibility to hydrogen embrittlement of grain boundary.
    (2) The KIH value decreases with increase of fracture surface transition temperature, vTrs(°C), grain size, d(mm), and hydrogen content, C(ppm).
    (3) The KIH value has a good correlation with the hydrogen embrittlement susceptibility factor, Φ, denoted by
    Φ=0.05d-1/5 (vTrs + 133) + 4 (log d2 + C1/3)
    (4) On the basis of the relation between KIH and Φ and some diagrams to determine the maximum residual hydrogen content in a pressure vessel wall, a safety estimation method for preventing HSC during hydrostatic test of pressure vessels after the service was proposed.
  • Development of an Apparatus for Determination of Diffusible Hydrogen in Steel

    pp. 277-284

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    A new apparatus for the determination of diffusible hydrogen in steel has been developed by using a gaschromatograph, thermal conductivity detector, and sequencer.
    The characteristics of the apparatus are as follows :
    1) The lower limit of detection is 10-5ml (N.T.P.), that is 5 × 10-4ppm for 2g specimen.
    2) The minimum cycle time of measurement is 3min.
    3) Fifteen samples can be measured in parallel when the measurement is carried out every one hour.
    4) The measurement shown above is automatically carried out by a programed sequencer.
    5) The coefficient of variance of results (approximately 4ml/100g) is about 1%.
    The apparatus is useful not only for determination of diffusible hydrogen in weld metal but also for determination of diffusivity of hydrogen in iron, alloy-steel and thin foil of amorphous iron and for measurement of permeability of hydrogen through steel.
    It was also revealed that for low hydrogen content specimens the glycerine volumetric method gave much lower results than those obtained by the present method.
  • Measurements of Dispersed Bubbles within Molten Iron Contained in a Small Induction Furnace

    pp. 285-292

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  • 珍答案と迷論文

    pp. 290-290

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  • 抄録

    pp. 293-294,292

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