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

Tetsu-to-Hagané Vol. 90 (2004), No. 10

  • Transition of Steel Flow Control Technology in a Continuous Casting Mold

    pp. 751-757

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    It was explained that the purpose of the fluid flow control in a continuous casting mold is to improve the inner or/and surface quality of the products, and characteristics of various flow control method are discussed. Submerged nozzle design, electromagnetic stirrer, electromagnetic brake and soft contact casting are mentioned as flow control technology. Mainly, the explanation was carried out in detail on flow control technology using the electromagnetic force on the transition of past development. It is future important problem to understand the quantitative relationship between the quality of the products and steel flow characteristics in continuous casting mold.
  • Recent Advances of Evaluation Methods for Non-metallic Inclusions in Steel

    pp. 758-765

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    Methods for evaluation of inclusions in steel are reviewed in this paper. In characterization of inclusions in steel, it is required to measure their size distribution, composition and morphology as well as their amount. The size and amount of inclusions to be evaluated have been greatly reduced in ultra clean steel. On the other hand, a variety of oxides have to be analyzed in the oxide metallurgy where oxides are utilized as precipitation sites. Conventional methods such as chemical extraction and metallographic microscope observation have been improved or modified to meet these requirements. Applications of high frequency ultrasonic testing and fusion extraction using EB or cold crucible have been reported regarding evaluation volume or speed. Recent developments of other rapid methods including spark-OES, laser analyses and ESZ are also introduced.
  • Effects of Hydrogen on Mechanical Behavior of Steels

    pp. 766-775

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    Main features of hydrogen effects on mechanical behavior of steels have been reviewed. While the effects on macroscopic tensile properties are not definite, the increase in dislocation mobility by hydrogen appears as an enhanced stress relaxation the extent of which correlating with the susceptibility to failure. Hydrogen enhances the creation of vacancies during plastic deformation. The extent is susceptible to microstructures of steels and correlates with the susceptibility to failure. Flow localization in the presence of hydrogen is substantial, leading to shear instability. Characteristic fractographic features in hydrogen-related failure, such as striations, have been shown to originate in deformation bands in which the density of defects is high. Prominent localization of void nucleation takes place at the advancing crack tip. Amorphization has been observed in front of the crack and just below the fracture surface in a hydrogen-charged steel in accord with flow localization and associated vacancy creation. Hydrogen remarkably reduces the fatigue resistance of steels, and, conversely, prior fatigue treatment increases the susceptibility to delayed fracture. The mechanism has been ascribed to the creation of vacancies during fatigue and interactions between vacancies and hydrogen. Further studies for assessing the susceptibility to hydrogen-related failure have been suggested to be based on the accumulation of damage rather than hydrogen content.
  • Chlorine Behavior of Waste Plastics Recycling Process Using Coke Ovens

    pp. 776-780

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    At the advent of the 21st century, mankind is facing a global environmental problem, and the industrial sector is required to take initiatives in the establishment of recycling society for efficient utilization of natural resources. To establish the waste plastics recycling method by using, iron-making process, waste plastics recycling process using coke ovens was developed by Nippon Steel in 2000. In this process, waste plastics are charged into coke ovens with coal, and carbonized at about 1200°C under the reducing atmosphere. Waste plastics are converted to chemical products, such as coke, tar and light oil, and coke oven gas.
    However, waste plastics involves chlorine-contained plastics, such as polyvinyl chloride and polyvinylidene chloride, etc. It is generally known that such chlorine-contained plastics cause corrosion problem at the incinerator or gasification equipment.
    Therefore, the behavior of chlorine content of waste plastics was investigated. As a result, it was found that the chlorine content of waste plastics is mostly pyrolysed during carbonization with coal in a coke oven and effectively captured by ammonia liquor.
  • Precipitation Behavior of Cu and MnS at High Temperature in Fe-10mass%Cu Alloys

    pp. 781-787

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    Copper (Cu) in steels is usually considered as a harmful tramp element, because it causes surface cracking at high temperature. Cu also retards recrystallization in aluminum-killed steels. On the other hand, Cu is useful for increasing hardness of steels and improving r-value in IF steel sheets. In this study, Fe-10mass%Cu alloys were investigated to observe the precipitation behavior of Cu and MnS at high temperature using a confocal scanning laser microscope. After the in-situ observation the precipitates were analyzed by SEM and 200 kV FE-TEM. As a result, the three types of Cu precipitates were found. "A" type is the liquid Cu forming at the austenite grain boundaries. "B" type is the ε-Cu precipitate at the non-metallic inclusions inside the austenite grains. "C" type is the fine ε-Cu precipitate in the grains. It was found that Mn and S added to steels helped a lot of CuS precipitates to form with (Mn, Cu)S ("B" type) and increased the number of Cu precipitates ("B" and "C" type) inside the grains.
  • Precipitation Behavior of CuS and MnS at High Temperature in Fe-C-Sn Steels

    pp. 788-794

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    Tin (Sn) in steels is a tramp element and promotes copper (Cu) to cause surface cracking at high temperature. But the detail has not been clear enough. In this study, Fe-0.05mass%C-3mass%Sn and Fe-0.05mass%C-0.3mass%Sn steels were investigated to clarify the effects of tin, manganese and sulfur on the precipitation behavior of tin, copper and MnS at high temperature. Under the two heat treatment conditions, the in-situ observations were carried out using a confocal scanning laser microscope. The first condition was a continuous cooling procedure and the second was an annealing procedure at 1423K. After the observation the precipitates were analyzed by SEM and 200 kV FE-TEM. As a result, in Fe-0.05mass%C-3mass%Sn steels the tin carbides were found as Fe3SnC mainly at the grain boundary. In Fe-0.05mass%C-0.3mass%Sn steels tin precipitates were not found at all. (Mn, Cu)S and fine CuS precipitates were found only inside the grains.
  • Determination of Trace Amount of Tin in Iron and Steel by Pre-column Derivatization/Reversed-phase High-performance Liquid Chromatography with 2-(5-Bromo-2-pyridylazo)-5-(N-n-propyl-N-sulfopropylamino)phenol

    pp. 795-800

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    A novel method for the determination of trace amounts of Tin in iron and steel has been demonstrated by a reversed-phase HPLC using 2-(5-Bromo-2-pyridylazo)-5-(N-n-propyl-N-sulfopropylamino)phenol (5-Br-PAPS) as a derivatizing reagent. Certified reference materials of iron and steel were used to prepare digestive samples by decomposition with sulfuric acid and hydrogen peroxide solution followed by benzene extraction with iodide. The digested sample solutions were derivatized with 5-Br-PAPS solution in acetate buffer (pH 3.0) solution. Aqueousmethanol (45 : 55 w/w) containing 0.5 mol kg-1 acetic acid and 5.0×10-3 mol kg-1 of tetrabutylammonium bromide was used as an eluent and was monitored at 422 nm.
    A linear calibration was observed in the concentration range from 1×10-7mol dm-3 to 1×10-6mol dm-3. The detection limit (3σ) of TinIV was 2.3×10-8 mol dm-3, which corresponded to 2.7 ppm in iron and steel samples. The recoveries of TinIV added to the digested solution of iron and steel were with in 94.8% to 110%. The good recovery and high sensitivity indicate that the proposed system is of great promise for the determination of tin present in iron and steel.
  • Mg-contained Zn Electroplating from Aqueous Solution Containing Quaternary Ammonium Salt

    pp. 801-806

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    Electrodeposition of Zn with Mg was tried using the rotating cylindric cathode in sulfate solutions containing Zn2+, Mg2+ and quaternary ammonium salt at 60°C under galvanostatic conditions. Mg was codeposited with Zn when the Zn deposition was significantly suppressed by the addition of stearyle benzyl ammonium chloride (C18-Benzyl) to the solution. The content of Mg in deposits was increased with an increase in the polarization of Zn deposition by additive C18-benzyl. The content of Mg in deposits was related to the content of C18-benzyl in deposits. XPS spectra of the deposits showed that Mg element in the deposits existed in bivalent state at low flow rate. However, in the deposits at high flow rate, the peak of Mg2s spectrum existed between bivalent and metallic Mg, suggesting that the chemical state of Mg may be changed depending on the flow rate. The duration to red rust occurrence in salt spray corrosion test was five times longer in Zn-0.4%Mg electroplated steel sheet than in electrogalvanized steel sheet.
  • Effect of Carbon and Chromium Contents on Latent Heat of Pearlite Transformation of Steels

    pp. 807-811

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    Differential scanning calorimetry was used to obtain information about the latent heat and the temperature of phase transformations in hypoand hyper-eutectoid steels, cast irons and chromium alloy steels. The tests by DSC apparatus were conducted with a heating process to 1000°C at a constant rate of 5°C/min and with a cooling process to 300°C at same rate. In the heating process, the latent heat of the pearlite to austenite transformations increases rapidly to the carbon content up to eutectoid and decreases proportionally above. Each peak temperature of phase transformation shows an increase with the chromium contents. In the heating process, the latent heat of 5% and 10% chromium contents is approximately half the amount of 0%. The latent heat of phase transformation has a constant value for all chromium contents in the cooling process. The empirical expressions of the start temperature of phase transformation for chromium contents were confirmed for their effectiveness of SUJ2 (high carbon chromium bearing steel).
  • Effect of Mn Content on Simulated HAZ Toughness of Large Heat Input Welding in Ti-Oxide Bearing Steel

    pp. 812-818

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    The effect of Mn content on simulated heat affected zone toughness of large heat input welding in Ti-oxide bearing steel was examined. A simulated heat affected zone microstructure is classified into four regions: i) a microstructure mainly composed of fine-grained ferrite, ii) a mixed microstructure composed of coarse grain boundary ferrite, ferrite sideplate and intra-granular ferrite, iii) a microstructure mainly composed of intra-granular ferrite, and iv) a mixed microstructure composed of intra-granular ferrite and martensite-austenite constituent with varying Mn content and peak temperature. The best simulated heat affected zone toughness was shown when the microstructure was mainly composed of intra-granular ferrite in Mn content of 1.71%. The simulated HAZ toughness also had a good relationship with effective grain size for fracture defined as a maximum thickness of grain boundary ferrite and ferrite sideplate in the range of peak temperature from 1350 to 1450°C. The simulated heat affected zone toughness began to deteriorate due to the formation of martensite-austenite constituent even when the microstructure was mainly composed of intra-granular ferrite in Mn content of 1.95%.
  • BN Type Inclusions Formed in High Cr Ferritic Heat Resistant Steel

    pp. 819-826

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    In order to make clear the formation and re-dissolution behavior of boron nitrides in high Cr ferritic heat resistant steels during heat treatment at high temperature, SEM observations of the fractured steel rod samples were carried out. A large number of coarse size BN type inclusions grown to 2 to 5 μm were distributed at bottom of dimples.
    During annealing at 1150°C, coarse size BN type inclusions were not dissolved, but at 1200°C coarse size BN type inclusions had a tendency to dissolve reducing its particle size with time and all BN type inclusions were re-dissolved completely in a short time at 1250°C.
    From the chemical analysis of boron and nitrogen in several high Cr heat resistant steels and SEM observations of its fractured samples, it was found that the critical boron and nitrogen concentration for formation of coarse size BN type inclusions are 0.001% B and 0.015% N, and the equation related [%B] and [%N] is represented as log[%B]=-2.45log[%N]-6.81.
  • Relationship between Tensile Properties and Casting Defect of Ti-29Nb-13Ta-4.6Zr for Biomedical Applications Cast by Dental Precision Casting Process Using Various Investment Materials

    pp. 827-834

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    Relationship between tensile properties and casting defect of newly developed β type titanium alloy, Ti-29Nb-13Ta-4.6Zr, for biomedical applications, and representative α+β type titanium, Ti-6Al-4V ELI, for biomedical applications cast by dental precision casting using commercial alumina, magnesia and modified magnesia based investment materials. Then the effect of specimen diameter on tensile properties of both cast alloys was also investigated.
    Elongation of cast tensile specimens of both alloys slightly increases and strength of cast tensile specimen of Ti-6Al-4V ELI increases with reducing casting defects. Hardness of surface reaction layer decreases, and hardness of matrix decreases by about 50 Hv due to increasing cooling rate by reducing the specimen diameter from 3 to 2 mm in both alloys. The microstructures of both cast alloys refines with reducing specimen diameters, and the hardness of surface reaction layers and matrix of both alloys decreases. Therefore, increasing strength of cast Ti-6Al-4V ELI with reducing specimen diameter is attributed to reducing casting defects.
  • Evaluation of Microstructural Factors of High Chromium Ferritic Steel Based on Analysis of Anelasticity Behavior at High Temperature

    pp. 835-840

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    Deformation behavior after abrupt stress loading at 923 K was investigated on ASME-P92 steel in the as tempered condition and after creep. Anelastic deformation originated from elastic bending of lath boundaries occurs in the crept specimen as well as the steel in the as tempered condition. Instantaneous plastic strain after stress increment was not observed up to 200 MPa in the tempered and crept specimen, except for the specimen crept up to tertiary stage in which the instantaneous plastic strain occurs under higher stresses larger than 150 MPa. Magnitude of anelastic displacement after stress reduction decreases with creep deformation, indicating that contribution of lath boundaries to anelastic deformation is small in the crept specimens in contrast with the tempered specimen. Lath boundaries migrate and annihilate during creep, resulting in increase of lath width. Therefore, number of lath boundaries contributing to the anelastic deformation decreases with creep deformation, meaning that anelastic displacement of the crept specimens is lower than that of the tempered specimen. The anelastic displacement decreases with increasing lath width, indicating that evaluating the anelastic displacement can be used as an assessment of change of the lath structure during creep deformation.
  • Influence of Heats, Heat-treatments and Strain Control Mode on High Temperature Fatigue Lives of 2.25Cr-1Mo Steels for Boiler and Pressure Vessels

    pp. 841-845

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    High temperature fatigue tests were conducted for normalized and tempered 2.25Cr-1Mo steels of three heats. As compared with the reference data, the influence of heats, heat-treatments and testing conditions such as testing temperature, strain rate and strain control mode on the high temperature fatigue lives were investigated. The results obtained are as follows.
    1) Heats of the normalized and tempered 2.25Cr-1Mo steels scarcely affected the fatigue lives at high temperatures.
    2) Between annealed and normalized and tempered 2.25Cr-1Mo steels there was scarcely difference in the fatigue lives.
    3) Strain rate between 10-3 and 10-2/s scarcely affected the high temperature fatigue lives of 2.25Cr-1Mo steel.
    4) Strain control mode and testing temperature affected the fatigue lives. In this case the strain control modes are axial and diametral.
    5) From these results, the ASME fatigue design curves of 2.25Cr-1Mo steel for nuclear components were unconservative for the data tested under axial strain control at each temperature. Modified design curves were proposed for normalized and tempered 2.25Cr-1Mo steels.
  • Comparative Study on the Analysis of Cast Iron Using Glow Discharge Mass Spectrometry and Spark Discharge Optical Emission Spectrometry

    pp. 846-851

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    We examined the feasibility of applying the glow discharge mass spectrometry (GD-MS) to the analysis of cast iron. Using 10 standard reference materials of cast iron, including NIST SRM, BS CRM, and BAS CRM, we obtained the relative sensitivity factors (RSFs) of C, Mg, Si, P, S, V, Cr, Mn, Ni, Cu, and Mo. We also performed comparisons with spark discharge optical emission spectrometry (SP-OES). Determination of alloying elements such as Si and Ni in cast iron by GD-MS revealed no bias among our study specimens, and the fluctuations of the RSFs in RSD were around 3%. For carbon, an important element, however, some specimens exhibited a low ion intensity ratio from GD-MS but a high emission intensity ratio from SP-OES. We suspect the cause of this lies in the metallic texture related to Fe and C, and the performed observation of EPMA. Therefore, we judged the cause when using GD-MS is the difference in ionization efficiency between graphite and matrix (cementite), or selective sputtering, and the cause when using SP-OES is abnormal discharge resulting from deposited graphite.
  • Effect of Film Properties on Bending Formability of Prepainted Steel Sheets

    pp. 852-857

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    Mechanical and viscoelastic properties of 54 polyester resin systems were measured, and the relationship between the properties and bending formability of prepainted steel sheets on which paints based on the polyester resin systems were applied was investigated. We found that formability increased with increasing elongation and tensile strength of the resin films, and the grass transition temperature (Tg) of the resins strongly influenced on the properties of resin films. We observed that elongation plotted versus Tg of the resin films measured at 20 degree Centigrade showed maximum peak in the resins' Tg around 30 degree Centigrade region, because resins which had low Tg below 30 degree Centigrade showed entropy elasticity at 20 degree Centigrade. On the other hand, tensile strength of resin films increased monotonously with increasing Tg of the resins. Tg of the resins also dominated shape of stress-strain curve (S-S curve). Finally, we proposed that it was important to obtain excellent bending formability that resins were in grass transition range in circumstances in which the prepainted steel sheets were actually used because the area surrounded by the S-S curve was larger compared with the other cases so that the fracture energy of the films was larger, and resins had higher elongation in the mentioned condition.

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