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

Tetsu-to-Hagané Vol. 81 (1995), No. 9

  • Revision of the Standard Method (JIS G 1253) for Spark Discharge Atomic Emission Spectromety of Iron and Steel

    pp. 869-875

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  • Oxidation of Aluminum in Molten Iron by Impurity Oxygen in Argon

    pp. 876-881

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    Oxidation rate of aluminum in molten iron by impurity oxygen in argon is observed in order to take information on evolving nonmetallic inclusion as well as nozzle blocking of continuous casting apparatus. The aluminum is oxidized by argon containing oxygen above 10-14 Pa in oxygen partial pressure.
    Rate determining step of the oxidation in the case of no convection is diffusion process in an oxide layer generated at the surface of the molten iron.
    In the case of specimen with convection, the step is chemical reaction process. The rate is expressed as a second order reaction for aluminum content. Apparent activation energy of the reaction is -1224 kJ/mol. It is discussed that the apparent activation energy corresponds to enthalpy change of the oxidation reaction.
  • A Quantitative Description of Void Distributions in Blast Furnace Raceway

    pp. 882-887

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    A void distribution in a blast furnace raceway significantly affects the results of numerical simulations for the raceway combustion zone. Despite its importance, technical difficulty in measuring this physical property had left a quantitative description out of reach.
    In the present paper, the direct measurement of raceway void distributions was attained in a three-dimensional cold model with the aid of laser sensors. Measured void fractions clarified the typical distribution pattern in a raceway, showing the inlet region with relatively high and constant void fractions(the gas core region) from the tuyere tip to the middle part of the raceway, followed by the linear decrease of voidage toward the raceway boundary. The extent of the gas core region was used to achieve the non-dimensional representaion for the axial void distribution, and was successfully estimated by the newly established correlation between a gas core length(DM), a tuyere diameter(DT) and a raceway factor (Rf), expressed by DM/DT=0.0963Rf0.546.
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  • Interfacial Tensions between Mutual Interfaces of Liquid Iron, SiO2-Al2O3-MnO-MnS Slags and MnS Based Sulfide

    pp. 888-893

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    Interfacial tensions between liquid MnO-SiO2-Al2O3(sat)slag/liquid iron of varying sulfur content, MnS based sulfide/liquid iron, and MnO-SiO2-Al2O3(sat) slag/MnS based sulfide were studied at 1550°C using Sessile Drop Method. The interfacial tensions, σ, between liquid MnO-SiO2-Al2O3 slag/liquid iron were found to be 0.164 to 1.10 N/m, depending on sulfur and oxygen contents in liquid iron and they were expressed by the following equation as a function of sulfur and oxygen activities :
    1.07-σ = 0.235 ln(1+10as+120as)
    Precipitation of MnS based sulfide under the condition of adding more than 20mass% MnS to the slag was observed to occur at the slag-metal interface. The interfacial tensions between MnS based sulfide/liquid iron as well as MnO -SiO2-Al2O3(sat) slag/MnS based sulfide were found to be 0.114 and 0.077 N/m, respectively.
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  • Improvement of Transverse Corner Cracks in Continuously Cast Hypoperitectic Slabs

    pp. 894-899

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    Solidification proceeds inhomogeneously in hypoperitictic steels (medium carbon steels) with carbon contents in the range of 0.08 to 0.16%. Therefore, longitudinal and transverse cracks easily occur on the slabs in molds. Soft cooling in mold, improvement of the mold powder and decrease of the amount of secondary cooling water have been carried out to prevent these surface cracks.
    In the slabs cast at Kakogawa Work's No.3 CCM, transverse corner cracks have been found on the slabs with increase in casting velocity. The cracks occur along deep oscillation marks. Mold powder component and segregation of Mn and P are detected in the vicinity of the cracks. This suggests that these cracks are generated in mold. The mechanism of crack formation is considered from analysis of the relation between transverse corner crack frequency and casting conditions. Based on the analysis, the transverse corner cracks are successfully prevented by such means as supression of the meniscus level fluctuation of molten steel, increase of the mold powder consumption and optimization of the taper on narrow face of mold.
  • Effect of Applied Stress on Flatness of Cold Rolled Austenitic Stainless Steels during Low Temperature Annealing

    pp. 900-905

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    In some cases, cold rolled austenitic stainless steels are heat-treated at a low temperature to improve the threshold value of spring and the fatigue life. Also, the flatness of stainless steel strips is improved by tensile loading given during such low temperature annealing. In order to find suitable condition for better flatness, the relationship between the strain and the stress evolved during low temperature annealing for 1 hour is investigated by heat-treating cold rolled stainless steels. The following conclusions are obtained; (1) The strain increases linearly with tensile stress up to 600N/mm2. and the slope to stress is as small as the reciprocal of Young's modulus. (2) A tensile stress near 200N/mm2, which is far below the yield strength, is required to improve the flatness of the strips, because of the small slope to stress. (3) The mechanism of micro deformation at low temperatures is considered to relate with stress relaxation, because most of plastic strain is evolved during heating to the annealing temperature.
  • Room Temperature-Coloration of Stainless Steel by Alternating Potential Pulse Method

    pp. 906-911

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    A film exhibiting interference colors is formed on stainless steel when immersed in a hot solution containing chromic and sulfuric acids, and the applied process is known as the "INCO" method. In this method, the driving force of the coloring reaction is mainly caused by the thermal energy, and the reaction should be performed at elevated temperature (about 80°C). The reproducibility of colors obtained is very poor since it is very difficult to terminate the coloring reaction immediately, to maintain high temperature, and to treat such aggressive solution. Therefore, the coloration of stainless steel is expected to take place at room temperature. In the present study, the coloring reaction was carried out in a chromic and sulfuric acid solution by applying alternating potential pulses at room temperature, and a relatively large-sized electrolytic cell was used to aim an industrialization. The uniformity of the colored film was sensitively dependent on the distribution of current rush in the solution. The sort and brightness of the colors thus produced stood well in comparison with those obtained by the conventional coloring at high temperature.
  • Solidificatation Process of High Speed Tool Steel Type Cast Iron for Rolls

    pp. 912-917

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    The phase diagram and the solidification processes are investigated on a series of alloy specimens containing 5%Cr. 5%Mo, 5%W, 011%V and 1.04.4%C. δ, γ, MC and M3C appeare as primary phases, and eutectics of γ+MC and γ+ M3C crystallize at boundary compositions between liquidus surfaces of the constituent phases. The compositional extent of each liquidus surface is similar to those of Fe-V-C and Fe-5%Cr-V-C alloy system. M2C and M7C3 crystallize as eutectic carbides because of segregation of Mo, W and Cr to residual liquid, though they don't appear in the diagram. The species and amount of carbides of this alloy system are estimated on the basis of the diagram and the analysis of redistribution of alloying elements.
  • Phase Transformation and Compositional Partitioning in TRIP Steel

    pp. 918-923

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    Transformation behavior and compositional partitioning in TRIP (Transformation induced plasticity) steel was investigated by means of microstructural observation and computer modelling. Orthoequilibrium partitioning of alloying elements of Si and Mn was attained even in short intercritical annealing time. A model based on transformation mechanism controlled by C diffusion well described the volume fractional change of ferrite and pearlite during the cooling to austempering temperature. Slower cooling rate significantly increased C concentration to around 0.5% in untransformed γ and caused pearlite transformation. Bainite volume fraction obtained by austempering increased with austempering temperature. Analysis by computer modelling revealed that transformation kinetics above 350°C followed the model based on diffusion mechanism, while it agreed better with the model based on shear mechanism below 350°C.
  • Stacking Faults of γ″ Phase Precipitated in a Ni-15Cr-8Fe-6Nb Alloy

    pp. 924-929

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    The stacking faults of a metastable γ″ phase precipitated in a nickel-base superalloy, a modified NCF 3 type alloy (X-750M), were investigated by transmission electron microscopy and X-ray diffraction method. The γ″ precipitates are circular shaped plates at the early stage of aging and they become elliptic or irregular shaped plates at the latter stage of aging up to 1033K. Contrast which suggests the existence of stacking faults on {112}γ″ planes can be seen in many of large γ″ precipitates extracted from the specimens aged at 1033K. It is clear that the values of γ″/γ lattice mismatch increase with increasing the aging time from the measurement of lattice constants of the γ and the γ″ phase. The formation of stacking faults on {112}γ″ in the large γ″ precipitates is due to the movement of an a/6 [111] partial dislocation introduced by γ″/γ coherency strain. Since a part of stacking sequence has a similar crystal structure to that of a stable δ phase precipitates in γ phase, the formation of stacking faults in the γ″ precipitates is considered to be favorable for the stabilization of them.
  • Fatigue Crack Propagation in Beta Ti-15Mo-5Zr-3Al Alloy

    pp. 930-935

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    Fatigue crack propagation (FCP) in beta Ti-15Mo-5Zr-3Al alloy has been studied in laboratory air for five different microstructures which were solution-treated at 700°C, 735°C, 765°C, 850°C, and 1000°C followed by aged at 500°C. With one exception, microstructure was found to have very little or no influence on FCP behaviour. The one exception was the microstructure having the largest beta grain size whose FCP resistance was higher than that of the other microstructures due to higher crack closure levels. The effect of stress ratio on FCP could not be realized only in terms of crack closure mechanism, because static fracture mechanisms operated in FCP behaviour depending on the magnitude of the maximum stress intensity factor. Furthermore, the FCP resistance of all the microstructures was considerably lower than that of alpha-beta Ti-6Al-4V alloy, which was primarily attributed to lower crack closure levels of the present alloy.
  • Effects of Microstructure, Simulated Body and Living Body Environments on Fracture Characteristics of Implant Material Ti-5Al-2.5Fe

    pp. 936-941

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    Mechanical properties, fracture toughness and fatigue strength of implant material Ti-5Al-2.5Fe were investigated related to the microstructure. Effect of the simulated body environment on the fatigue strength and effect of the living rabbit body environment on mechanical properties and fracture toughness in Ti-5Al-2.5Fe were then investigated. The data of Ti-5Al-2.5Fe were compared with those of Ti-6Al-4V ELI and SUS316L.
    The equiaxed α structure which is formed by solution treatment at a temperature under β transus followed by air cooling and aging gives the best balance of mechanical properties in Ti-5Al-2.5Fe. Ti-5Al-2.5Fe exhibits much greater rotating bending fatigue strength compared with SUS316L and equivalent rotating bending fatigue strength to that of Ti-6Al-4V ELI in the both air and simulated body environments. Fatigue strength of Ti-5Al-2.5Fe in the simulated body environment is degraded by lowering oxygen content because the formability of oxide on the specimen surface is considered to be lowered comparing with in air. The mechanical properties of Ti-5Al-2.5Fe is not changed in the living rabbit body environment. The hard surface corrosion layer is, however, formed on the surface of SUS316L in the living rabbit body environment.

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