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

Tetsu-to-Hagané Vol. 88 (2002), No. 2

  • State of the Art in Integrated Thermodynamic Databases

    pp. 51-58

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    Integrated thermodynamic databases (ITDs) and its applications have been reviewed. Thermodynamic quantities and phase diagram of practical multi component steels and slags calculated by using the ITDs have been found to agree well with measurements. Transformation structure, precipitation and composition change of molten steel due to reaction with molten slag can be predicted by using process simulation model in which ITD is used as a subroutine program. Calculation accuracy depends on the experimental data which is used to determine thermodynamic parameters in the ITDs. From this viewpoint, it is very important to accumulate accurate experimental data. The following recent movements can be mentioned: 1) Calculation models for prediction of thermodynamic properties at surface/interface have also been developed. 2) Application programs such as analysis of solidification and refining have been built in the ITDs. 3) Ab initio calculation software has been available and its result have been converted to database for CALPHAD approach.
  • Behavior of Trace Chlorine in Sintering Bed and Its Effect on Dioxins Concentration in Exhaust Gas of Iron Ore Sintering

    pp. 59-65

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    Suppression of dioxins emission for iron are sintering is one of the most important and urgent needs. To the purpose, the basic research for the title is necessary. Sinter pot tests of sinter mixture adding Cl content were carried out, and the results obtained are as followed. (1) 20-40 mass% of Cl content in sinter mixture stays in sintercake. 20-40 mass% of volatile Cl content traps on raw material in sinter bed, while 60-80 mass% of that discharges to exhaust gas without trapping raw material. Trapped Cl content in raw material of sintering bed partly vaporizes again and partly stays at the sintering reaction. The volatile Cl content is mainly composed of metal-chloride such as NaCl, KCl and etc. (2) Dioxins concentration in exhaust gas is proportional to Cl content added to sinter mix by under 500 mg/kg. Source of Cl content in term of kinds of chemical compond also affects on dioxins concentration in exhaust gas. KCl, poly-vinyl-chloride, NaCl, CaCl2, high Cl are are rank in order of much concentration of dioxins. Volatile Cl content and organic content are effevtive factors of dioxins occurrence. The dioxins concentration in the experimental case of high Cl content at upper layer is more than those in the case of uniform Cl content, but in the case of high Cl content at lower layer the dioxins are as same as those.
  • Application of the Direct Resistance Heating for Stainless Steel/Aluminum Clad Manufacturing Process

    pp. 66-72

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    Clad steel sheet is formed by cladding different metals and used for the functional material, which has convenient characteristics of each metal. Especially, a lot of stainless steel/aluminum clad strip is produced for electromagnetic rice cookers which are in demand because of the higher thermal conductivity, having magnetism and corrosion resistance. For the demand, continuous cladding technology of the wide width stainless steel/aluminum strip has been developed by warm rolling after the rapid heating process. Recently, much higher uniformity for peeling strength is required as the market grows. So, a new heating process, in which uniform heat generation is achieved by the electric resistance of metals and the directly applied current, is developed in place of the conventional process of induction heating. After solving some technical problems about sparks and temperature uniformity, direct resistance heating equipment have installed in the manufacturing line. As the result, high-quality clad steel sheets, which have the uniform peeling strength, can be produced by the improvement of temperature deflection on rolling.
  • Improvement of Pitting Corrosion Resistance of Spring Steels for Automobile by Alloying and Chemical Passivation Treatment

    pp. 73-80

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    In order to reduce an exhaust gas, it has been necessary to reduce a weight of automobile. One of the most effective method for the weight reduction of cars is the strengthening of parts. Therefore, in order to reduce the weight of suspension coil springs, the strengthening of spring steels has been carried out in recent years. However, the strengthening of steels brings increase in sensitivity for corrosion fatigue caused by pitting corrosion.
    Improvement of the pitting corrosion resistance by alloying and chemical passivation treatment was investigated in this research. Measurements of anodic polarization curves were carried out for four commercial production low alloy spring steels and 22 laboratory steels modified on JIS SUP 10 in 5 mass% NaCl solution at 308±0.5K.
    Furthermore, the effect of chemical passivation treatment on the pitting potential was evaluated for the specimens treated in 63 mass% conc. HNO3 solution at 308K. The quasi-pitting potential of V'cq100 corresponding to V'c100 of stainless steels, has been adopted to evaluate the pitting corrosion resistance of low Cr-bearing spring steels.
    The major results of this research are as follows.
    (1) The effective alloying elements to improve the pitting corrosion resistance of the low alloy spring steels are Si, Ni, Cr, Cu, Co, Sb, and B.
    (2) The chemical passivation treatment for 3.6 ks on the practical spring steels containing less above-mentioned alloying elements, is also effective to improve the pitting corrosion resistance.
    (3) The quantitative alloying design guide based on regression analysis between V'cq100 and content of alloying elements was proposed.
  • Hydrogen Embrittlement and Corrosion Fatigue Caused by Pitting Corrosion of Spring Steels for Automobile with Improved Pitting Corrosion Resistance by Alloying Elements and Chemical Passivation Treatment

    pp. 81-87

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    The strengthening of spring steels has been carried out for weight reduction of automobile in recent years. However, the strengthening of the steel increases sensitivity to corrosion fatigue and hydrogen embrittlement through pitting corrosion in NaCl solution.
    In previous report, authors have made clear that alloying and chemical passivation treatment improve the pitting corrosion resistance of the low alloy automobile spring steels. In this research, the effects of these two improving methods on the corrosion fatigue and hydrogen embrittlement were investigated.
    The slow strain rate tensile (SSRT) test at ε=6.7×10-6s-1 of strain rate and two kinds of corrosion fatigue tests were carried out for the automobile spring steels, JIS SUP12 and a high pitting resistance spring steel (HDS13) after wet-dry cyclic corrosion in 5 mass% NaCl solution at 308K.
    One of the fatigue tests was done under the corrosion condition with dropping 5 mass% NaCl solution on the surface of the specimens.
    The results of this research are as follows.
    (1) The hydrogen embrittlement caused by the pitting corrosion producing hydrogen permeation into the steel was found from the intergranular brittle fracture surface propagated from around a corrosion pit of specimens.
    (2) It was found that the HDS13 having high pitting potential (V'cq100) with effective alloying elements showed superior hydrogen embrittlement resistance and corrosion fatigue strength.
    (3) It was found that the addition of alloying elements which inhibit the pitting corrosion and the chemical passivation treatment were effective to decrease corrosion fatigue and hydrogen embrittlement sensitivity of low alloy spring steels.
  • Prediction of Forming Limit Diagram (FLD) and Effect of Work Hardening Property on FLD of Sheet Metals

    pp. 88-94

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    The necking limit diagram NLD and the forming limit diagram FLD under the wide-range bi-axial tensile stress conditions were obtained by using various sheet metals of steels, Al-alloys and a copper. The good correlation between the limited strain values of NLD and FLD and the mechanical properties of total elongation and r-value etc. were obtained. Moreover, the strain dependency of the work hardening coefficient n-value in higher strain area was different according to each material. The complex value of n-value and r-value was defined as the equivalent work hardening coefficient neq-value in higher strain area. And when the neq-value was substituted to Gotoh's modeling of localized necking limited strain, FLD that accuracy is high was able to be predicted.
  • Effect of Mo and W on Creep Characteristics of Precipitation Hardened Carbon Free Martensitic Alloys

    pp. 95-100

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    A new attempt has been demonstrated using carbon free Fe-Ni-Co martensitic alloys strengthened by μ-phase and Laves phase to achieve homogeneous creep deformation at high temperatures under low stress levels. Creep behavior of the alloys is found to be completely different from that of the conventional high-Cr ferritic steels. The alloys exhibit gradual change in the creep rate with strain both in the transient and acceleration creep regions, and give a larger strain for the minimum creep rate. In these alloys the creep deformation takes place very homogeneously and no heterogeneous creep deformation is enhanced even at low stress levels. The minimum creep rates of the Fe-Ni-Co alloys at 700°C are found to be much lower than that of the conventional steel, which is due to fine dispersion strengthening useful even at 700°C in these alloys. It is thus concluded that the Fe-Ni-Co martensitic matrix strengthened by μ and Laves phases is very useful to increase the creep resistance at elevated temperatures over 650°C.
  • Observation of Morphologies in Ti Films after Deformations of Ti-coated (011)[100] Si-steel Single Crystals

    pp. 101-106

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    In order to clarify the crack morphology after 180° bend-forming and bulge press-forming of Ti films deposited on (011)[100] single crystal of silicon steel, Ti coating by the hollow cathode discharge (HCD) method was done on polished single crystal sheets, and then the Ti-coated samples were 180° bend-formed or bulge press-formed, and then observed by the scanning electron microscope.
    Ti-coated silicon steel of (011)[100] single crystal sample showed no distinctive crack in Ti films on steel sheet, on which slip lines at intervals of 15μm to the [1210]Ti direction could be observed in a rectangular-like morphology 1025μm in width and 1560μm in length.
    The slip morphology of bulge press-forming of Ti films was different from that of 180° bend-forming; the former process produced slips and kinks but no distinctive cracks due to the creation of of a complicated slip systems arising from areal deformation, and the latter process produced fine single slips due to the creation of a single system arising from unidirectional deformation.

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