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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 61 (1975), No. 8

  • 科学における専門分野の在り方

    pp. 1999-2000

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  • The Behavior of Oxygen during Direct Current Electroslag Remelting

    pp. 2001-2011

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    By the use of a small scale unit for the DC-electroslag remelting, pure iron and carbon steels, S55C and SK3, were investigated with slags CaF2, CaF2-20%Al2O3 and CaF2-20%CaO.
    The results obtained are as follows:
    1) Oxygen concentrations of ingots remelted in CaF2 slag were measured, when iron electrode wasconnected positive, DCRP, and negative pole, DCSP. Based on the difference of oxygen concentrations, about 50% of oxygen, which was transfered from the slag into the molten metal at the tip of theelectrode, was eliminated through the slag/metal boundaries of molten pool and falling drop at DCRP.
    2) Ratios of O2- and AlQ33- ions as oxygen carriers from slag to metal could be estimated for boththe polarities by the comparison of oxygen concentrations in ingots remelted in the CaF2 and CaF2-Al2O3 slags. The elimination of Al2O3 in the molten metal at the tip of the electrode through the slag/iron boundaries of falling drop and metal pool was estimated to be about 50%.
    3) The elimination of elements must be discussed on the basis of the difference between cleanliness (a mass transfer from metal phase into slag phase) and contamination (a transfer of reverse direction).The former is not affected by the scale of remelting, but by slag composition and boundary conditions.The later, however, is related closely with the scale of units, i. e, the current density.
  • Some Turbulent Fluid Flow Problems in Steel Processing Operations

    pp. 2012-2027

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    Through the use of turbulent flow theory a mathematical representation is proposed for a range ofsteel processing operations where turbulent mixing plays a major role in determining the efficiency ofthe process. The resultant differential equations were solved numerically, using a digital computer.
    The examples discussed in the paper include mixing in argon-stirred ladles, the flow patterns in theliquid pool of continuous casting systems, the flow field induced by an electromagnetic force field incontinuous casting and flow patterns in rimming ingots.
    The computed results indicate that velocities as high as 30 cm/s may be found in these systems andthat the eddy diffusivities may have values as high as 500 cm2/s. The computed results were found tobe in reasonable semi-quantitative and in some cases quantitative agreements with results of experimentalmodel tests. While the computer requirements are quite substantial, some 5-10 minutes on a CDC6 400 (state university of New York at Buffalo), the approach outline here seems attractivebecause it provides a much improved insight into the structure of the flow field and a more solid basisfor further studies of inclusion coalescence, inclusion entrapment, electromagnetic stirring, and mass transfer in steel processing.
  • The Effect of Strength and Work Hardening Characteristics on the Headability of Austenitic Stainless Steel Wires

    pp. 2028-2037

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    There have been studied the effects of volume fraction of martensite, stacking fault energy, austenite grain size and solid solution hardening on the strength, work hardening behavior and other mechanical properties of austenitic stainless steel wires. We tried to evaluate systematically the headability of the relationship between the mechanical and physical properties and the headability.
    The main results are as follows:
    (1) The work hardening behavior (n-value) is mainly decided by volume fraction of martensite and stacking fault energy, that is, steel KSS 70 containing 3% Cu (18Cr-9Ni-3Cu) and SUS 384 (16Cr-18Ni) show lower n-value than SUS 305 J 1 (18Cr-13Ni) as a result of high stacking fault energy even in the presence of strain induced martensite.
    (2) The yield strength becomes higher with the increase of solution elements such as C, N, and Mo and with the decrease of austenite grain size following the Petch relationship.
    (3) In SUS 304-7 (18Cr-8Ni), the n-value and elongation decrease slightly with the increase of austenite grain size. On the other hand, a contrary tendency is seen in the stable alloys such as SUS 384, 385, 305 J 1 and etc. In the tensile test, the reduction of area gradually decreases with the increment of grain size.
    (4) There can be seen an obvious relationship between the headability of each specimen ranked from 1st to 8th and the hardening factor H. F., defined as yield strength times n-value, that is, the low hardening factor results in an excellent headability.
    (5) Factors affecting headability can be classified to two groups such as;(i) strain induced martensite, stacking fault energy, and grain size which affect headability as a result of the change in yield strength and n-value, (ii) inclusion, surface scratch, and heading technique which affect headability without change in yield strength or n-value.
  • The Toughness of As-Quenched Ni-Cr-Mo Steels

    pp. 2038-2050

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    The toughness of Ni-Cr-Mo steels containing a small amount of V or/and Nb was estimated for as quenched conditions in relation to the austenite grain size. The toughness was quantified with the experimentally determined critical J-value, formulated by J. R. RICE, using small size three-point bending specimens.
    The results obtained are as follows;
    (1) The critical stress intensity factor calculated from the critical J-value is in satisfactory agreement with measured plane strain fracture toughness K1c in the range of large scale yielding.
    (2) The tensile properties deteriorate with coarsening of austenite grain. The toughness of the steels, on the other hand, remains nearly constant through a wide range of austenite grain size, showing a gradually decreasing tendency with the grain growth. However, all specimens with the largest grain in each series of the steels show a discontinuous deterioration in fracture toughness because of grain boundary fracture.
    (3) The fracture toughness of the steels used is in a good correlation with the size of dimples, which originate at small inclusions. The toughness is, therefore, almost independent of the austenite grain size, as the austenitizing treatment results in no change in the mean spacing of the points responsible for dimple fracture.
    (4) The steels with a small amount of V or/and Nb indicate the tendency to a better fracture toughness compared with those containing no Nb.
  • Microfractographic Studies of Temper Embrittled Steel

    pp. 2051-2060

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    The testing temperature dependence of the fraction of intergranular fractures was investigeted in brittled the fracture of temper embrittled low alloy steels after Charpy impact tests. Quantitative measurements of the fraction of intergranular fractures in microscopic brittle fracture, which consists of quasi-cleavage and intergranular fractures excluding ductile fracture in macroscopic brittle fracture, were made using the point count technique applied to electron microfractographs.
    It was found that intergranular fracture increases with the increase of fracture temperature and transgranular (quasi-cleavage) decreases with it. Intergranular and transgranular fracture strengths were discussed following Griffith-Orowan equation for brittle fracture accompanying plastic deformation on the fracture surface, and the change in fracture modes would be attributed to the temperature dependence of the plastic energies accompanied by the formation of the fracture surface, since the plastic energies would be dominant in the effective surface energies accompanied by the brittle fracture surfaces.
    The variation of the fraction of intergranular fracture as a function of phosphorus and molybdenum contents, and the intergranular fracture in temper embrittled ferritic-pearlitic steel were also investigated.
  • The Relation between the Influence of Various Elements upon the Graphitization of White Cast Iron and Their Crystal Structures

    pp. 2061-2066

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    Many elements have been used for present investigation on the problem in question and the following results have been confirmed:
    1) All the elements having face centred cubic lattice favour the graphitization of white cast iron of Fe-C-J system (J is any element). However the element, which favours the graphitization of white cast iron, is not limited to that having face centred cubic lattice.
    2) The elements having close-packed hexagonal lattice resemble to those having face centred cubic lattice, and most of the elements belonging to this group favour the graphitization of white cast iron.
    3) Most of the elements which hinder completely the graphitization of white cast iron are included in the elements having body centred cubic lattice.
  • The Effect of Recrystallization Texture on the Low-Temperature Deformation Behaviour of a Two-Phase Stainless Steel

    pp. 2067-2075

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    The tensile properties, the strain-induced martensite transformation and the fracture mode in the temperature range between-196°C, and room temperature were studied for a two-phase steel composed of nearly equal volumes of austenite and ferrite. Recrystallization textures were observed in both the austenite and ferrite phases. Tensile test specimens were taken in the directions parallel (θ=0°C), 45°C, and vertical (θ=90°C) to the rolling direction.
    The main results obtained are as follows:
    (1) Effects of the anisotropy due to the texture on tensile properties (fracture elongation, tensile strength, and 0.2% yield strength), amount of strain-induced martensite transformation, cleavage crack length, and dimple size were measured. The transformation had a marked effect on fracture elogation and tensile strength.
    (2) The transformaticn-induced plasticity was evaluated with both the amount of martensite transformed per unit strain and the tensile strain at the initiation of transformation in austenite phase. As the initiation strain for martensite transformation bacame larger, the fracture elongation increased. At a constant tem perature the larger the amount of martensite per unit strain was, the larger the fracture elongation was. This phenomenon was clearly observed at -50°C. All of the strain-induced martensite in the low temperature range was observed as lath-like martensite.
    (3) The behaviour of ferrite phase in the low temperature range gave characteristic aspects to the fracture mode. Cleavage cracks occurred in {001}α planes and their propagation was disturbed at spots of a martensite, therefore specimens didn't fail brittlely in the low temperature range. The cleavage crack length observed on fractured surface was in maximum at -196°C and had the length of about 35 microns at θ of 45°C. Equiaxed dimples were about 5 microns in the maximum size at -50°C in the case of 0°C or 45°C-specimen.
  • Temperature Measurement System of Steel Strips in a Continuous Annealing Furnace

    pp. 2076-2087

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    In order to measure the temperature of steel strips in continuous annealing furnaces with inert or reducing gases, following items were studied;
    (1) The characteristics of emissivity of the steel strips were experimentally studied, which depended on the specification and the temperature of the strips as well as the wavelength of a detector.
    (2) Shielding method of stray radiation: energy from furnace walls or heat sources was studied in detail from theoretical and experimental points of view.
    This stray energy was found to depend on the shape and the surface condition of the shielding flange, gap between the strip and the flange, the wavelength of a detector and the temperatures of the furnace wall and the steel strip.
    On the basis of these results, the system was designed and was made up of radiation pyrometers with the shielding flanges and of contact thermometers for intermittent correction.
    The estimated error of the measurement was less than 1%.
  • The Quality of Stainless Steel Slab Produced by Pressure Casting

    pp. 2088-2098

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    The salient features of the pressure casting are a precisely controlled rate ofpouring and a smooth surface of the mold coated with fine alumina powders. Under a suitable operation, the pressure casting process provides a excellent slab surface free from tears and blow holes. Since argon gas purges the mold atmosphere from oxygen, reoxidation of steel is completely prevented duringcasting. The oxygen content of a pressure cast slab is lower than that of a conventional ingot of the same heat, and most oxide inclusions found in the slab are the primary deoxidation products. Aluminacoatings retard effectively the initial rate of solidification, and the amount of inclusions entrapped in the vicinity of the surface is reduced drastically compared with that of a conventional ingot.
  • Effect of Impurity Elements on Temper Embrittlement of Nickel-Chromium Steels

    pp. 2099-2106

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    Temper embrittlement of the nickel-chromium steels containing P, As, Sb, Sn, or Mo has been investigated. The impact properties of the non-embrittled steels quenched after tempering and of the embrittled steels step-cooled following tempering were studied by the instrumented Charpy test.
    Susceptibility to temper embrittlement was measured by comparing the transition temperature and the effective surface energy of nonembrittled steels and the step-cooled steels. The embrittling treatment applied to steels with Sb, P or Sn caused very much increase in transition temperature, but the same treatment applied to the steels with As or Mo caused less increase in transition temperature. The mechanical properties of the steels embrittled by step cooling were characterized by the low fracture load, low effective surface energy and the small deflection of the specimen to fracture.
    The fracture mode of the step-cooled or the non-embrittled steels tested at low temperatures was of intergranule along the prior austenite grain boundary or of quasi-cleavagerespectively.
    The technique of Ion Micro spectroscopy and the Auger electron spectroscopy used to study the segregation of impurity elements to prior austenite grain boundaries, and it was found that Sb, P and Sn segregated at grain boundaries during tempering of the steels containing Sb, P or Sn.
  • Study and Development of Electrode Steel Wires for Gas Shielded Metal Arc Welding

    pp. 2107-2114

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    The study of CO2, gas shielded arc welding process invented by. H. SEKIGUCHI, was begun in 1953 to develop it in wide practical use, and it has been conducted with regard to the following three phases:
    (1) study and development of electrode steel wires for CO2, (or CO2-O2) gas shielded arc welding process; improved arc-stability and notch toughness of weld metal and developed many kinds of commercial wire.
    (2) development of wire manufacturing techniques; improved wire feedability, prevented wirecurling and developed automatic wire spooling machine.
    (3) application to welded structures and expanding applications; proved the usefulness of the process in application to rear axle-housings and idlers.
  • Carbon Deposition in the Reduction of Iron Ore by CO under High Pressure

    pp. 2115-2117

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    An apparatus of the differential thermal analysis under high pressure (approx. 100kg/cm2, max. temp. 700°C) was used to investigate carbon deposition in CO atmosphere during the reduction.
    Pulverized hematite are (Swaziland, Brazil), magnitite are (Mosan) and carbonyl iron powder wereused as test samples. The results were as follows.
    When initial CO pressure was 20kg/cm2, the carbonization of CO took place at around 390°C on hematite and at 4302 on magnetite. When the pressure was increased to 50kg/cm2, it was observed that the reaction temperature was lowered by abut 402. It was also confirmed that metallic iron played as catalizer for the carbonization of CO at around 550°C.
  • Interfacial Tension between Molten Iron Alloys and Molten Slags

    pp. 2118-2132

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  • 抄録

    pp. 2138-2143

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