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

Tetsu-to-Hagané Vol. 68 (1982), No. 7

  • Present Status on the Structural Determination of Molten Ferrous Alloys and Ferrous Slags (1)

    pp. 711-719

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  • Phosphatability of Cold Rolled Steel Sheet for Automotive Bodies

    pp. 720-731

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  • On the 7th Comparative High Temperature Tensile Testings

    pp. 732-739

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  • Influence of Size Degradation of Sinter on the Blast Furnace Operation

    pp. 740-749

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    Fundamental experiments on the degradation of sinter during reduction were carried out and the correlation between the reducing conditions and the degree of size degradation was evaluated quantitatively. On the basis of these results, the size degradation of sinter in the blast furnace was estimated and the influences of size degradation on the blast furnace operation were investigated.
    (1) The effects of reducing conditions can be summarized as follows.
    a) At any temperature, the rate of decrease in size is reduced with the increase in reduction degree. When the reducing temperature is below 525°C, the size degradation is related only to the reduction degree and is independent of the reducing temperature.
    b) The size degradation becomes remarkable with the increase in initial size before reduction.
    c) The CO concentration and the flow rate of reducing gas do not substantially influence the degradation behavior, but exclusively influence the reduction rate.
    (2) The decrease in sinter size due to the degradation during reduction lowers the gas permeability in the blast furnace.
    (3) When the sinter size in the furnace decreases, the gas utilization becomes worse due to the change in gas flow and the fuel rate increases. On the contrary, when the sinter size becomes excessively large, the fuel rate decreases due to the decrease in reducibility and low gas utilization by the decrease in reduction surface. Therefore, it is expected that the optimum sinter size in the furnace exists.
  • Reduction of Molten Iron Oxide in CO Gas Conveyed System

    pp. 750-758

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    The kinetics and mechanism of reduction of molten iron oxide with CO gas at high temperatures of 1450°C and 1600°C were investigated. In order to reduce the influence of mass transfer rate on overall reaction rate of reduction, fine powders of iron oxide were used as specimen and were reduced in a transport reactor. The specimens of fine powder of reagent grade were melted during falling down in reaction zone and liquid oxide drops were reduced with CO gas. Mean diameter of liquid particles was 25μ.
    The oxide particles were melted and became spherical, and the reduced iron was surrounded by liquid FeO. It is considered that liquid FeO always existed on the spherical surface and the nucreation, growth and cohesion of iron in liquid drop did not influence the overall reaction. The results were analysed by considering only the mass transfer in a gass film and the chemical reaction at the gas liquid interface.
    The value of mass transfer coefficient kg was estimated by using the Ranz-Marshall equation. Considering the shrinkage of particles by production of metallic iron, the values of rate constant of chemical reaction kc were obtained as 19.4cm/s at 1600°C and 9.3cm/s at 1450°C.
  • Thermodynamics of Chromium Oxide in Molten CaO-MgO-Al2O3-SiO2 Slags Coexisting with Solid Carbon

    pp. 759-766

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    The equilibrium concentrations of Cr in the molten CaO-MgO-Al2O3-SiO2 system with Cr3C2, C, and one atmosphere of CO were determined at 1500°C and 1650°C. Chromium in the slag was found to exist as CrO from a thermochemical consideration. The activity coefficients of CrO, γCrO were calculated from the determined concentrations. The Cr2+ ion in the melts was found to behave amphoterically with a critical (SiO2) concentration of 30 wt%. In the CaO-Al2O3-SiO2 melts, Al2O3 was observed to increase γCrO in the region where chromium oxide behave as base. Therefore the equilibrium concentration of chromium decreased with increasing (Al2O3) at constant CaO/SiO2. In the system of CaO-MgO-Al2O3-SiO2, the effect of (Al2O3) was complicated, because of the existance of MgO. The γCrO values were found to have close relationship with γTiO1.5 and γMnO.
  • Permeability and Apparent Diffusivity of Oxygen in Molten Iron Oxide-CaO-SiO2 System

    pp. 767-773

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    Permeabilities of oxygen through molten iron oxide-CaO-Si02 have been measured by means of the penetration method through molten film developed by the authors.
    The permeability of oxygen increased with increasing iron oxide content when the content was low. However it decreased with increasing iron oxide content above 30wt%.
    This phenomenon was explained on the basis of the theory for high temperature oxidation of metals by C. Wagner. From the present results, it was found that the apparent oxygen diffusivity can be determined. This can be used for the calculation of oxygen transport rate through the molten slag under non-steady state.
  • Statistical Analysis of Gas Bubbles Dispersion in Liquid Phase

    pp. 774-783

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    Nitrogen gas was injected into water through a vertical nozzle which was placed at the bottom center of a cylindrical container. Bubbes dispersed in water were detected by electroresistivity probes. Time series data obtained were processed with a micro-computer and subjected to statistical analyses. It was shown that the bubble dispersion was a stochastic process and horizontal distribution of the bubble frequency was represented by a two dimensional Gaussian curve around the jet axis. Cone angle of the bubble dispersion zone was defined explicitly from the locus of threefold standard deviation of the distribution on a vertical plane through the jet axis. The cone angle varied noticeably with the geometry of water vessel which would affect the profile and velocity of the circulating flow in the bulk water. Local rising velocity of bubble was determined by taking cross correlation of two time series data which were obtained from two probes located close each other along the rising path. Size distribution of bubbles was determined locally by a new method which was originated from quantitative stereology. It was shown that the measurement of time series by the electroresistivity probes coupled with the statistical analyses was helpful to investigate the spread and structure of bubble dispersion zone in electrically conductive liquids.
  • Mechanism of Formation and Method of Detection of Breakout Caused by Sticking between Mould and Slab in Continuous Casting of Steel

    pp. 784-793

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    A sticking type breakout in continuous casting which is distinguished from the ordinary one caused by buldging at the thin shell of slab corner, was investigated in regard to the effect of operation factors, mechanism, and method for detection.
    The breakout occurred more frequently after changing the plating material of the mould from Cr to Ni. The breakout frequency decreased by using mould powder with lower viscosity. The thickness of the shell remained in mould after breakout was thicker near meniscus than that at the lower position and then increased downwards. A part with very thin or ruptured shell, which was defined as "constricted line", is formed in an inclination of 30° to 45° downwards to horizontal. The breakout occured at a position where the constricted line crossed the exit line of mould. Ripple marks with narrow pitch formed on the surface of both sides of the constricted line in parallel with the constricted line.
    On the basis of the results, a mechanism of this kind of breakout was proposed, that is, the breakout is caused by sticking between mould and slab near meniscus due to lack of mould slag inflow. Two kinds of detection system of the breakout were developed.
  • Rheological Analysis of Bulging of Continuously Cast Slabs with Elementary Bending Theory

    pp. 794-798

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    The bulging of the shell in continuously cast steel slabs between the retaining rolls has been computed in terms of elementary bending theory. Creep and elasto-plasticity are taken into account at the same time as the factors influencing the bulging. The calculated results are as follows:
    i) Bulging pattern comprises concave zone around the exit and convex zone near the inlet of a retaining roll.
    ii) The depth of the above mentioned wave is larger than that of conventional bulging as measured at the middle of the roll span.
    iii) The bulging calculated by the present study depends sensibly on the parameters for the stressstrain relationship of the material.
  • Relation between Microstructures and Low Temperature Toughness in Extra Low Carbon 11Ni Steel

    pp. 799-808

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    The effects of microstructures on low temperature toughness have been studied in the fine-grained extra low carbon 11Ni-1 Mo-0.5Mn steel which has a very low sensitivity to temper embrittlement.
    Low temperature toughness was examined on the basis of the relation between yield strength and transition temperatures. The excellent low temperature toughness of this steel was mainly attributed to the inherent toughness of tempered martensite matrix. One kgf/mm2 decrease in yield strength at room temperature of matrix lowered transition temperature by about 25K, which was the fairly large value as compared with the previously reported values in high tensile strength steels or 2.5 to 3Ni cryogenic steels. The fresh martensite increased transition temperature even if the amount was very small. The stability of retained austenite against plastic deformation was very poor contrary to the stability against sub-zero treatments. The effects of the retained austenite on low temperature toughness depended morphologically on its size and distribution. The retained austenite lowered transition temperature without the loss of yield strength when its thickness was less than 0.1 μm and further it was isolated from each other. However, when the phase grew larger and coalesced together, it turned to be disadvantageous to low temperature toughness.
  • 主要国における科学技術の総合力を示す各種指標/研究関係従事者数/学術文献の引用数からみた研究の水準/「グラフ」昭和56年の日本鉄鋼業の動き/製管の歴史(3)-ユジーヌ・セジュルネ法-

    pp. 808-808,842

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  • Substructural Change during Low-cycle Fatigue of SUS 316 at Elevated Temperature

    pp. 809-818

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    The substructural change during low-cycle fatigue of SUS316 stainless steel at elevated temperature has been investigated by X-ray diffraction and transmission electron microscopy, and its correlation with the fatigue hardening behavior has also been shown. Fatigue test was performed under a total strain range of 1.0% with a strain rate of 4×10-4 sec-1 at 600, 700 and 800°C.
    The main results obtained are as follows:
    (1) The saturation hardening stage at tained after around 100 cycles at 600°C, 12 cycles at 700 °C and a few cycles at 800°C.
    (2) At 600°C, the particle size (<D>e) decreased markedly with increasing cycles up to 10 cycles and varied little afterwards. At 700°C, <D>e decreased in the hardening stage, became constant in the earlier stage of the saturation hardening stage but increased at the later stage. At 800°C, <D>e became 3000040000Å at the earlier cycle and varied little afterwards.
    (3) At the saturation hardening stage, <D>e changed little but microstrains varied markedly within one cycle. Storage, relief, storage and relief of strain energy are repeated in one stable hysteresis loop. As a result, it seems that there is little net' change in stored energy within one cycle.
    (4) It seems that the stress range (Δσ) at the hardening stage depends on the dislocation density (ρ) and the relation between them is given by Δσ/2bG=1.05×105+0.96√ρ where G is the shear modulus.
  • Creep Fracture Behavior and Metallurgical Factors affecting Rupture Ductility of 0.5 Mo Steel

    pp. 819-826

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    Creep fracture behavior and metallurgical factors affecting rupture ductility have been studied for the improvement of rupture ductility of 0.5Mo steel. The heats of the steel exhibit minimum rupture ductilities of 310% in elongation and 413% in reduction of area when tested at 450° and 500°C.
    The decreases in ductilities correspond with the transition in fracture modes from transgranular to intergranular creep fractures. Intergranular creep fracture is caused by grain boundary cracking such as wedge-type one under higher stresses and by formation of cavities associated with grain boundary carbide particles under lower stresses. The effect of surface cracks on rupture properties is relatively insignificant although the mean length of the cracks is much longer than those of the grain boundary cracks and cavities.
    Main factors affecting the grain boundary cracking and the cavitation in 0.5Mo steel are grain size, amounts of impurities, and size and distribution of grain boundary carbide particles. It was confirmed that higher ductility than that of 1Cr-0.5Mo steel is easily attained without reduction in rupture strength by means of controlling these factors.
  • Nonequilibrium Austenite Phase in Melt-quenched Fe-C-Mo and Fe-C-W Alloys

    pp. 827-836

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    By melt-quenching technique, nonequilibrium austenite alloys possessing high strength and hardness combined with good ductility have been found in Fe-C-Mo and Fe-C-W ternary systems. This formation region is limited to about 1.02.4 wt%C and 322 wt%Mo for Fe-C-Mo and 1.02.4 wt%C and 324 wt%W for Fe-C-W. The austenite phase has ultre-fine grains of about 0.2 μm in diameter. Their Vickers hardness and tensile strength increase with increase in the amounts of C and Mo or W, and the maximum values attain about 710 DPN and 1450 MPa for Fe-C-Mo and about 700 DPN and 1500 MPa for Fe-C-W, respectively. Elongation increases with decreasing C and Mo or W contents and reaches about 2% for Fe-1.4%C-9%Mo and Fe-1.4%C-15%W. The relatively large elongation at low concentrations of C and Mo or W results from the transformation-induced plasticity of austenite to martensite. In addition, the changes in microstructure and mechanical properties of the tempered austenitic alloys have been investigated and it has been observed that a large secondary hardening occurs in a wide range of about 600900 K for Fe-C-Mo and 500900 K for Fe-C-W. The hardening is due to bainite transformation from austenite to ferrite and M3C in the temperature range from 500 to 700 K and due to the formation of carbide in the range from 700 to 900 K and martensite transformation after tempering. Thus the present alloys may be attractive as fine gauge high-strength materials.
  • Effect of Heat Treatment on Some Properties of 0.8C-4Cr-4Mo-1V Steel

    pp. 837-842

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    In order to find the most suitable heat treatment method of 0.8C-4C-4Mo-1Y steel, the effects of various factors of heat treatment (austenitizing temperature, tempering temperature, and number of times of tempering and sub-zero treatment) on microstrcture, amount of retained austenite, hardness, impact toughness, fracture load and deflection in bending test and wear resistance were investigated. It has been found that the most suitable austenitizing temperature of this steel is 1120±10°C, the suitable codition of tempering is 530-550°C, the suitable codition of tempering is 530-550°C for 2h by 3 times, and it is unsuitable to use a sub-zero treatment for this steel.
  • Effect of Misorientation on Intergranular Corrosion and Intergranular Stress Corrosion Cracking of Type 304 Steel with Coarse Columnar Crystals

    pp. 843-849

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    The effects of misorientation on intergranular corrosion in boiling H2SO4-CuSO4 and boiling HNO3 solutions and on intergranular stress corrosion cracking in FeCl3 solution were investigated on type 304 steel with coarse columnar crystals. As the deviations of the growing direction around <100> orientation were within 10°, the grain boundaries were treated as simple tilt boundaries with <100> rotation axis.
    The depth of interglranular corrosion, DI, and the depth of intergranular stress corrosion cracking, DC, of the specimen water-quenched, followed by sensitization at 923K for 7.2ks clearly decreased at coincidence boundaries (Σ13, Σ17, and Σ5) and the grain boundaries with rotation angle, ω, which were less than 10°and more than4 0°. DI and DC of the specimen water-quenched, followed by sensitization at 823K for 7.2ks after strained to 3.0% clearly decreased at coincidence boundaries and at the grain boundaries with ω which were more than 40°. However, DI and DC changed over a wide range at the grain boundaries with ω which were less than 10°. Schmid factor of component crystals was larger for deep DI and DC, and was smaller for shallow DI and DC. This suggests that DI and DC do not only depend on ω but also on the degree of plastic deformation near grain boundaries.
    According to observation of carbide precipitation at grain boundaries, carbides were recognized at random boundaries, but not recognized at coincidence boundaries and the grain boundaries with ω which were about 45°.
  • Mechanism of the Formation of Sulfide Stains on Tinplate

    pp. 850-857

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    In tinplate cans filled with sulfur-containing foodstuffs such as fish and meat, tin reacts with H2S and HS- ion produced by thermal decomposition of content during pasteurization and sulfide stain is formed inside of cans. The effect of tin crystal faces, tin oxide and passivation film by cathodic dichromate treatment on the sulfide staining was studied and noted on the mechanism of sulfide stains by transmission electron microscopic techniques.
    The summary is as follows:
    (1) Sulfide stain on tinplate cans packed with tuna was identified by electron diffraction as stannous sulfide SnS. The degree of tin sulfide stain depend on tin crystal orientation, and the closely packed (010) and (110) planes are more stable against sulfide staining.
    (2) Tin sulfide staining is prevented by passivation film, the staining on passivated tinplate starts at the sites uncovered with passivation film and tin oxide is peeled at the interface of tin and tin oxide by growth of SnS. When nuclei of stannous oxide SnO are formed during baking of lacquer, the staining starts at them.
    (3) The sulfide staining is inhibited by formation of passivation films at defect sites of tin oxide. And stannic oxide SnO2 on tin layer act as barrier layers against the formation of SnS.
  • Development of a Blow-Hole-Gas Analyzer and Its Application

    pp. 858-862

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    A new apparatus to determine the composition of gas in blow-holes in steel has been developed. A steel specimen is pierced in a vacuum vessel by means of a drill which is driven by a motor placed outside the vessel. The vacuum vessel is directly connected with a quadrupole mass spectrometer which analyzes the released gas from blow-holes.
    It is demonstrated that analysis of the gas in cavities in steel using the new apparatus has assisted in the investigation of the origin of the cavities.
  • Giant Pulse Laser Spectrochernical Analysis of C, Si, Mn in Solid Steel

    pp. 863-871

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    A method of spectrochemical analysis by means of G. P. (giant pulse) laser has been applied to the analysis of C, Si, Mn in solid steel and its most suitable condition has been studied. The following results have been obtained:
    (1) In atmosphere of the analysis, Ar or Ar+3%H2 is better than N2 and air from the point of view of spectral intensity and SN ratio.
    (2) As a result of examinations of influence of laser energy on spectral intensity and intensity ratio, it is generally suitable to set up laser energy above 0.3J. And for the purpose of minimization in variations of each analysis, intensity ratio to Fe II 271.4nm should be used.
    (3) In the most suitable condition described above, calibration curves have been made and its relative errors of analysis have been evaluated.
    (4) As a result of the time profile studies of the spectral lines obtained in Ar atmosphere, it has been shown that the separation of line and background is possible, and so that SN ratio of the analysis is much improved by this technique.
  • Giant Pulse Laser Direct Spectrochemical Analysis of C, Si, Mn in Liquid Iron

    pp. 872-880

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    For the purpose of the process control in continuous steelmaking, a new method of G. P. (giant pulse) laser direct spectrochemical analysis of C, Si, Mn in liquid iron has been developped. This method is characterized by coincidence of optical axis of laser and spectrometer. In this study, fundamental conditions for the analysis of C, Si, Mn, especially taking a serious view of C, has been studied. The following results have been obtained:
    (1) Influence of variations in the level of liquid iron surface on spectral intensities and intensity ratios has been evaluated. It has been shown that, for the purpose of minimization of these influences, intensity ratio should be used.
    (2) Si and Mn analysis are possible with the use of cylinder type and cone type atmosphere controlling apparatus.
    (3) In C analysis, it has been shown that CO gas generated in the surface of liquid iron have effects upon spectral intensity of C I 193.1nm, and these effects can be eliminated by using cone type atmosphere controlling apparatus. C analysis is possible with the use of this apparatus.
  • 抄録

    pp. 891-894

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