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

Tetsu-to-Hagané Vol. 79 (1993), No. 9

  • Trends of Hot Working Tool Steels in Recent Years

    pp. 1013-1021

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  • The Characterization of Precipitation and Role of Grain Boundary Chromium Carbide on the IGSCC Resistance of Nickel Base Alloys

    pp. 1022-1031

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  • Effects of Initiation of Reduction and Oxide Additives on Morphology of Iron Nuclei in the Reduction of Wustite with Hydrogen at 670°C

    pp. 1032-1038

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    The influence of initiation of reduction and of traces of impurity oxides added specifically and dissolved in FeO on morphology of iron nucleus formed by the reduction of dense wustite with H2 gas at 670°C has been investigated. The reduction was started in two ways: (1) the sample was heated to reduction temperature in vacuo and then H2 gas was introduced to the sample at various rates, (2) the sample kept at room temperature was inserted into the H2 gas stream kept at reduction temperature.
    When pure FeO was reduced in the procedure (1), porous nuclei (they are lenticular shapes and grow to form a porous layer which surface remain at the level of the sample surface) were not observed but were observed locally in the case of that H2 gas was introduced at the fastest rate. CaO favored porous nuclei particularly and MgO slightly. Al2O3 and SiO2 were unfavorable for porous nuclei. Iron nuclei precipitated in cooling period were observed on the surface of the sample when the sample containing CaO was cooled slowly after interruption of oxygen removal reaction.
    When samples were reduced in the procedure (2), surfaces of all kinds of samples were covered with porous iron. The influence of impurity oxide did not appear clearly.
  • Estimation of Phosphorus and Sulphur Distribution Equilibria in Bath Smelting Process

    pp. 1039-1045

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    The distribution equilibria of oxygen, phosphorus and sulphur between 1-10mol%FetO containing CaO-SiO2-Al2O3-MgO slag saturated with 2CaO·SiO2 and liquid iron were observed at steelmaking temperature in the present work to consider the distribution of each element in steady state between the slag and iron - carbon melt in bath smelting process.
    It was assumed that the oxygen potential at slag-metal interface was not controlled by the activity of oxygen in metal phase but almost done by the iron oxide activity in slag phase and the activities of phosphorus and sulphur in ironcarbon melt were equal to those in liquid iron equilibrated with the present slag. On this assumption, the distribution ratios of phosphorus and sulphur between the slag and iron - carbon melt were estimated at ironmaking temperature as a function of slag composition, carbon content in metal and temperature based on the experimental results.
    It was shown that the application of regular solution model to the slag could predict the distribution ratios of phosphorus and sulphur in bath smelting process at any slag composition, carbon content in metal and temperature on the above-mentioned assumption.
  • Cold Model Experiment for Developing a New Velocimeter Applicable to Molten Metal

    pp. 1046-1052

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    The objective of this study is to develop a new velocimeter utilizing the drag force of a sphere which is applicable to velocity measurement of high temperature molten metal flow. Although the drag coefficient CD is required for the evaluation of drag force, has not been studied for a fluid flow with high turbulence intensity and turbulence scale typical of ironmaking and steelmaking processes. Therefore, CD was measured using a sphere placed in a wind tunnel equipped with turbulence generator and correlated as a function of Reynolds number Re and turbulence intensity Tu. The effect of turbulence scale was found to be negligible.
    A new velocimeter using a sphere was developed and its applicability was examined in cold models such as an air jet of Tu_??_2%, a water jet of Tu=3040%, and a water-air bubbling jet of Tu=4050%. Agreement between the results obtained by the present velocimeter and those obtained by existing velocimeters, for example, Laser Doppler Velocimeter, hot wire anemometer and pitot tube was quite reasonable. Velocity measurement in a mercury-air bubbling jet also revealed the possibility of the usage of the present velocimeter for high temperature and high turbulence molten metal flow in metallurgical reactors.
  • Effect of Slit Design of a Cold Crucible on Magnetic Field Distribution and HeatGeneration Rate

    pp. 1053-1059

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    In order to clarify the effects of the design parameters of a cold crucible such as the width and the number of slits on the process variables, experiments and theoretical analyses were conducted. Magnetic field was measured and an aluminium charge was melted in cold crucibles with different slit widths. The two variables of electrical resistance and inductance were introduced into an equivalent circuit model of a cold crucible and their variations caused by the change of the slit width were calculated by use of the data obtained by measuring the input power and the coil voltage. Furthermore, the three dimensional magnetic field around a cold crucible system was calculated by using of the boundary element method. To confirm the accuracy of the circuit model and the numerical analysis, the variations of the electrical resistance computed by both theoretical ways were compared with each other. By use of the three dimensional computer code, the effects of width and number of slits on the heat generation rates in the crucible, the coil and the charge were evaluated.
  • Free Deformation of the Initial Solid Layer of Some Non-ferrous Alloys

    pp. 1060-1066

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    In order to elucidate the effect of deformation of initial solidified layer on surface defects of continuously cast slabs, the deformation behavior of freely solidifying disc was observed with several non-ferrous metals and their alloys by the droplet method. The following results were obtained:
    (1) After solidification and cooling to room temperature, the shape of the shell bottom of all the metals and alloys tested became parabolic.
    (2) Deformation of pure metals was positive, i.e. convex toward chill and was attributed to thermal contraction after solidification. A model for the prediction of deformation of pure metals was proposed and a fair agreement with experimental results was obtained.
    (3) Direction of deformation of alloys was either positive or negative, sometimes very large near eutectic, depending on the composition. This is because many alloys solidify to form supersaturated solid solution, from which a second phase precipitates causing expansion or contraction, depending on the difference of molar specific volumes of the two phases.
  • Reaction Mechanism between Alumina Graphite Immersion Nozzle and Low Carbon Steel

    pp. 1067-1074

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    Reaction between refractory and molten steel causes clogging in the immersion nozzle in continuous casting process. Reaction mechanism between alumina graphite nozzle containing silica and molten steel was studied on the observation of immersion nozzle after casting and the fundamental experiment. The results are summarized as follows,
    (1)The reacted zone with a lot of pores where contents of SiO2 and C decreased were observed in immersion nozzle refractory after casting.
    (2)The reaction in refractory was given by the following reaction formula as a whole,
    SiO2(s) + C(s) = SiO(g) + CO(g)
    (3)The overall reactions between Al killed steel and the alumina graphite refractory, and between Ti killed steel and the alumina graphite refractory were given by the following reaction formulas respectively,
    (Al killed steel): 3SiO2(s) + 3C(s) + 4Al = 2Al2O3(s)+3Si + 3C
    (Ti killed steel)
    low C, high Ti region: 5SiO2(s) + 5C(s) + 6Ti = 2Ti3O5(s) + 5Si + 5C
    high C, low Ti region: 5SiO2(s) + 5C(s) + 3Ti = Ti3O5(s) + 5Si + 5CO(g)
    (4)In SiO2-C refractory 50% of SiO2 was evaporated as SiO and the other 50% changes into SiC by the carbothermic reduction of SiO2. On the other hand, in Al2O3-SiO2-C refractory 100% of SiO2 was evaporated as SiO.
  • Dynamic Meniscus Behavior Influencing on Surface Condition of Products Cast in Continuous Caster with Alternating Magnetic Field Applied from the Outside of a Mold

    pp. 1075-1081

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    In order to understand the meniscus behavior in the pool of a continuous caster with high frequency magnetic field applied from the outside of the mold, a model experimental work was conducted by using molten gallium which has a low melting point (301.8K). The terms meniscus height, meniscus depth and intermittently contacting distance are newly defined and measured for precise study of the state of contact between the mold and molten metal. Contacting pressure between the metal and the mold was calculated and the dynamic meniscus behavior was measured indifferent relative positions of the coil and the molten metal surface. The meniscus oscillating conditions to provide a good surface quality were estimated by examining the relationship between the surface roughness of a cast tin and the dynamic meniscus behavior. It was found that the meniscus is not stationary but repeats an intermittently contacting between the mold and the metal. The intermittently contacting distance, the meniscus height and the meniscus depth can be controlled by the magnetic field intensity and the relative position of the coil. It is estimated that the intermittently contacting behavior plays an important role in improving the surface quality of cast ingots.
  • Effect of Cooling Rate on Oxide Precipitation during Solidification of Low Carbon Steels

    pp. 1082-1087

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    Effect of cooling rate on oxide precipitation during solidification was investigated using Ti and Al-Ca deoxidized low-carbon steels. The number and size distribution of oxides in the continuously cast steels have been observed and theoretically analyzed. The results obtained are as follows.
    The Ti deoxidized steel has more soluble oxygen before solidification than the Al-Ca deoxidized steel. With the increase in the cooling rate during solidification, the number of oxides increases and the size becomes smaller in the Ti deoxidized steel.
    During the solidification, segregation makes oxygen content increase above the equilibrium value with oxide in Ti deoxidized steel. The difference between the oxygen content increased by segregation and that in equilibrium is a driving force for the oxide growth. With increasing cooling rate, time for oxide growth decreases and supersaturation of oxygen for oxide precipitation increases. Consequently, the number of the oxide increases by the increase in the frequency of precipitates during solidification for high cooling rate.
  • Auger Electron Spectroscopy Analyses of the Interface of Titanium-Clad Steels with Ultra-low-carbon Contents

    pp. 1088-1094

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    Interface structure of Ti/Fe in the clad materials with ultra low carbon(ULC) steels and commercially pure titanium sheets have been studied to clarify the effects of various factors such as the preparation methods, the carbon contents in steels and the temperatures of heat treatments by using Auger electron spectroscopy(AES).Specimens were prepared by two kinds of methods, that is, hot isostatic press(HIP) and explosive bonding(EX). Carbon contents in the ULC steels were varied from 0.0045 to 0.03 mass%. Temperature ranges of heat treatments for 14.4ks in vacuum were varied from 773 to 1323K. As for the HIP specimens before heat treatments, it was found that there already existed strong differences in the Ti/Fe interface structures. Based on the measurements of EX specimens after heat treatments, it was suggested that the interface structure was mainly determined by the temperatures and the carbon contents. When the carbon content was more than 0.012mass%, it was found that TiC precipitated at the Ti/Fe interface with temperature rising up to about 1073K. TiC layers acted as barriers for the diffusion of metal atoms across the interface and delayed the growth of intermetallic compounds and β-Ti. Those diffusion barriers were re-dissolved at above 1173K.
  • Durability of Sprayed WC/Co Coatings in Al-added Zinc Bath

    pp. 1095-1100

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    In order to develop protective coatings for sink rolls used in continuous hot-dip galvanizing, the sprayed WC/Co cermet coating was formed on a mild steel by the High Velocity Flame Spraying system and its durability in the molten zinc bath (753K) containing 03mass%Al has been investigated on the basis of the constitutional change measured by SEM and EDX. The following results were obtained.
    1)During immersion periods, Al was enriched in the Zn-Al solution close to the sprayed coating surface and Al-rich phase was deposited on the sprayed coating surface.
    2)Under the sprayed coating surface, the diffusion layer, where Zn was rich and Co was poor, was built up. As Al content in the molten zinc bath was increased, the thickness of the diffusion layer was decreased and the durability of the sprayed coating could been kept for longer times.
    3)It is presumably a reason for such improvement of the durability that the Al-rich phase acts as a diffusion barrier for Zn and Co at the interface of molten zinc/sprayed coating and consequently depresses the growth of the diffusion layer.
  • Application of Hypereutectoid Steel for Development of High Strength Steel Wire

    pp. 1101-1107

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    The optimum patenting conditions for hypereutectoid steel to obtain a high drawability and a high work hardening rate were studied by metallographic examinations and laboratory drawing. Based on the present results, higher strength steel wire with small diameter has been manufactured on a production basis.
    1) Provided that an appropriate cooling rate corresponding to carbon content is secured, the precipitation of thick proeutectoid cementite can be prevented.
    2) In the practical patenting temperature range, the cementite plate thickness as well as the pearlite lamellar spacing decreases as the carbon content increases.
    3) The work hardening rate during drawing and the delamination resistance are enhanced through elimination of the upper bainite in pearlite.
    4) The maximum strength of 0.04 mm wire manufactured from 0.96%C-0.2%Si-0.3%Mn-0.2%Cr steel without delamination occurrence has reached to as high as 5.70 GPa.
  • Effect of Boron on Liquid Zinc Induced Embrittlement in Heat Affected Zone of STKT590 Steel Tube for Power Transmission Tower

    pp. 1108-1114

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    This paper represents the effect of boron on liquid zinc induced embrittlement in the heat affected zone of STKT590. To determine the susceptibility toward liquid metal zinc induced embrittlement at a fracture time of 400s (SLM-40), 64 kinds of carbon steel whose boron content was varied in 4 levels, have been tested by the notched-bar-tensile test method.
    SLM-400 is reduced linearly if a small amount of boron, less than 4 mass ppm, is added. In the case of more than 4 mass ppm of boron, SLM-400 is minimized to 10 to 20%. Therefore, boron is considered to intensify liquid zinc induced embrittlement, because the ferrite ratio at the grain boundary is reduced.
    Additionally, we reconsidered the JIS regression formula of carbon equivalent for susceptibility liquid zinc induced cracking (CEZ). As a result, a modified formula of CEZ was suggested to revise the JIS formula. This formula has been considered to be effective in predicting resistance to zinc induced cracking in large steel structures.
  • Creep Behavior Analysis of a 2.25 Cr-1Mo Steel under Accelerated Test Conditions

    pp. 1115-1121

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    Creep behavior has been studied of a 2.25 Cr-1Mo steel under accelerated test conditions. The experimental results show that the minimum creep rate, εm, is well expressed by an equation from wihch an Arrhenius term is absent. This fact implies that the state equation for minimum creep rate fails to reflect the unique rate controlling process relevant to the creep mechanism. In a strain region where ε>εmm:strain corresponding to εm), the value of ln εincreases linearly with increasing strain, and the slope of the straight lines decreases with increasing initial stress. This fact shows implicitly that microstructure becomes hard at high stresses and soft at low stresses although creep rate increases with increasing time. The relation between creep life (tr) and εm is expressed by an equation, εmY·tr= KM-G orεmY'·(trr)=KD-M, where Y, Y', KM-G and KD-M are constants. The time to minimum creep rate (tmin) was connected with creep life irrespectively of stress and temperature by an equation of tmin=0.111×tr1.07. When the extent of structural degradation is expressed by a minimum creep rate ratio of used to unused specimens, the remaining creep life of degraded materials is readily converted into the minimum creep rate ratio.
  • Deep Drawing of Commercially Pure Titanium Sheets

    pp. 1122-1128

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    The technology of deep drawing of commercially pure Ti cold-rolled sheet for obtaining drawn cup without defects was developed. Oil hydraulic press of max. 490 kN punch force and 98kN max. blank holding force (BHF) and 300mm/min drawing speed were used. Ti sheets (TP28C) of 0.8mm sheet thickness (t) were used. The punch diameter is φ40mm, and various punch radii were used
    First, blanks lubricated with machine oil were deep drawn. BHF values were calculated by Dr. Fukui's formula. The limiting drawing ratio (LDR) was about 1.8, inferior to steel sheets.
    Next, two 30μm polyethylene (PE) films were used on each side of the Ti sheet and BHF values were calculated by Dr. Fukui's formula. The LDR increased to 2.5, but large and numerous wrinkles were found. When the BHF was increased to 98kN, only traces of wrinkles were found. Last, punch lubrication was eliminated by the 50mm center hole of PE films of the punch side. The BHF was also 98kN. The LDR increased to 2.6, but severe earing was formed.
    As for the effect of rp on LDR, when rp is smaller than (46)t, LDR somewhat diminished.
    By adequate blank shape, this earing was nearly eliminated.
  • Rist Operating Diagram(I)

    pp. N618-N618

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  • Mechanical Properties and Strengthening Mechanisms of Powder Metallurgy Alloys Produced by Mechanical Alloying

    pp. N625-N630

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