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

Tetsu-to-Hagané Vol. 85 (1999), No. 5

  • Convenient Method of X-Ray Absorption Spectroscopy Using EPMA

    pp. 353-361

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    Fine structures in X-ray fluorescence spectra are explained from the view point of trace analysis. Among these fine structures, the physical processes of the X-ray Raman and radiative Auger effects are explained in detail. The similarity between the radiative Auger effect and X-ray absorption fine structures (XAFS) are described. A novel method to measure the XAFS spectra using the radiative Auger effect is explained; this method has been named EXEFS. Various numerical results of EXEFS Fourier analysis are described with the change of parameters in the numerical analysis. A potential of applying EXEFS method to microbeam analysis is reviewed.
  • Mechanism of Inclusion Deposition on Immersion Nozzle in Continuous Casting and the Role of Generated Inclusion by Reaction between Refractory and Molten Steel

    pp. 362-367

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    The mechanism of alumina buildup on immersion nozzles in continuous casting was studied by considering both inclusions suspended in the molten steel such as deoxidation products (suspended inclusions) and inclusions generated by chemical reaction in refractory and molten steel (reacted inclusions).
    (1) Two kinds of generation mechanism of reacted inclusions are considered as follows.
    a) alumina generated by the reaction at the interface between refractory and molten steel (interfacial reacted inclusions).
    b) alumina generated by nucleation when [Al]2[O]3 exceeds critical supersaturation degree in the concentration film layer near the interface between the refractory and molten steel (nucleation reacted inclusions).
    (2) The deposition rate of reacted inclusions is evaluated to be smaller than that of suspended inclusions. Therefore, inclusions deposited on the immersion nozzles may mainly originate from suspended inclusions.
    (3) At the early stage of alumina buildup, the network alumina is formed by deposition of interfacial reacted inclusions, nucleation reacted inclusions and suspended inclusions. Inclusions in the concentration film layer nucleation reacted inclusions and suspended inclusions are forced to move to the refractory due to the interfacial tension gradient formed by the concentration gradient of silicon etc.
    When the reaction in the refractory proceeds and oxygen feeding rate decreases, mainly suspended inclusions are deposited on the network alumina because the generation rate of reacted inclusions decreases.
  • Analysis of Inclusion Behavior in a Ladle Refining Process by a Newly Developed Coagulation Model

    pp. 368-374

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    A new model was developed to analyze the coagulation behavior of inclusions in the molten steel during the secondary refining process. The advantage of the model is to calculate the behavior of two types of inclusions, such as alumina inclusion and slag-origin inclusion, which is a slag particle engulfed by the flow at the surface of the molten steel. The flow of the molten steel in a ladle is calculated by using a large eddy simulation model, and several kinds of inclusion collision modes are considered in the coagulation model. Inclusion analysis experiments were carried out in the secondary refining process, changing the flow rate of Ar gas injected from bottom of the ladle; the results were compared with the calculation. It is concluded that the increase in Ar gas flow rate increases the number of inclusions by enhancing the slag particle engulfed at the surface of the molten steel. The effect of Ar gas flow rate on the number of inclusions seems to be small within the range of Ar gas flow rate investigated.
  • Reoxidation Behavior in Al Killed Steel during Casting

    pp. 375-381

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    The kinetics of reoxidation of Al killed steel with slag and air were investigated in laboratory experiments using tammann furnace and in plant experiments using commercial 85×103 kg tundish. Experimental results were discussed by the coupled reaction model.
    Observed apparent rate constants of [sol.Al] decreased with increasing (CaO)/(SiO2) ratio in laboratory experiments and showed a good agreement with calculated ones.
    Flow rate of air leak at steady state was evaluated to be 3.0×10-5 and 4.0×10-4 m3/s inside and outside of immersion tube in commercial tundish, respectively and was estimated to have little influence on reoxidation.
    Mass transfer coefficient in metal was estimated to be 6.0×10-5 m/s based on the tundish mixing model and the coupled reaction model.
    Observed [sol.Al] in tundish decreased with increasing (%FeO)+(%MnO) value in ladle slag and showed a good agreement with calculated one by considering reoxidation in ladle and air leak at unsteady state.
  • Relationship between Variation of Parameters and Behaviors of Coals during Heating

    pp. 382-386

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    For high-caking Warkworth and low-caking K-Prima coals, Geiseler plastometry, differential scanning calorimetry (DSC), proton magnetic resonance thermal analysis (PMRTA) and dynamic viscoelasticity were measured at a heating rate of 3°C/min under nitrogen. The amount of solvent-soluble constituent of the coals heat-treated at 3°C/min was also measured by using a solvent extraction with carbon disulfide-N-methyl-2-pyrrolidinone mixed solvent at room temperature, which gives high extraction yields for the heat-treated coals in the softening range. Changes in various chemical and physical parameters from the measurements were compared with one another to investigate the mechanism of softening and fusibility of coals. We suggest that the softening is occurred by a physical relaxation of aggregates in coal macromolecular structure and the amount of the solvent-soluble constituents greatly increases, resulting in enhancing the softening and fusibility. The mobility parameter from PMRTA, the viscoelastic parameter and Geiseler fluidity gave the maximum at similar temperature, showing that fusibility is the result of increased mobility of whole coal. The dynamic viscoelastic measurement was found to be a useful and convenient means for the study on caking behaviors of coals, since it can estimate concurrently both the fluidity and the elasticity of coals.
  • Investigation on the Manufacturing Condition of Ti-6Al-4V Seamless Pipes by Inclined Rolling Process

    pp. 387-393

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    Manufacturing conditions for Ti-6Al-4V alloy seamless pipes by inclined rolling process were investigated on laboratory scale. Elevated temperature torsion tests and piercing tests were carried out on Ti-6Al-4V alloy ingot and forged materials after various conditions. A portion of the pierced shell were hot rolled and annealed to predict microstructure and tensile properties of products by the inclined rolling process. The results were as follows.
    (1) Grain size affects deformability at elevated temperatures. Material with finer grain size possesses higher deformability as well as wider temperature range of high deformability in alpha+beta temperature region.
    (2) The material forged in beta region with coarse grain size possesses sufficient deformabilities for the piercing operation. There is no effect of the forging conditions on tensile properties after piercing operation.
    (3) The microstructure on the final products consists of fine acicular structure and their tensile properties satisfy the specification for Ti-6Al-4V seamless pipes.
    (4) Piercing temperature at 1373K and reheating temperature at 1223K are recommended for the inclined rolling process to avoid formation of grain boundary alpha phase which detoriorates ductility of the products.
  • A Generalization of the Taylor-Bishop-Hill Theories and the Rate-dependent Slip Model in Crystal Plasticity

    pp. 394-398

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    In the Taylor-Bishop-Hill theories of crystal plasticity for the prediction of deformation textures, the problem of determining the shear rate on a slip system in a particular crystallite is reduced to the optimization procedures under linear constraints. On the other hand, the rate-dependent slip theory which is modeled by a power law relationship between the shear rate and the resolved shear stress on a slip system is formulated as the non-linear simultaneous equations system with respect to the stresses. It has been recognized to date that the Taylor-Bishop-Hill theories are essentially distinct from the rate-dependent slip one. This paper is to generalize the Taylor theory by considering in terms of the mathematical programming scheme as a norm minimization problem in the finite dimensional Banach space, and then to demonstrate that the rate dependent slip theory is included in such generalized Taylor-Bishop-Hill crystal plasticity ones. Finally, the mathematical formulation for the extended relaxed constraints model including the rate-dependent slips is comprehensively presented based on the generalized Taylor-Bishop-Hill theories.
  • Properties of Silica-base Lubricant Film Coated Galvannealed Steel Sheets for Automotive Use

    pp. 399-404

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    The effect of a silica-base lubricant film on sliding property and spot weldability of galvannealed steel sheet was investigated by using hat channel drawing with bead and electrode tip life under the SiO2 coating weight of 10-100 mg/m2 in the silica-base lubricant film. (1) Sliding property is improved largely by coating the silica-base film of 10-20 mg/m2 as SiO2 on the galvannealed steel sheet. The reason seems to be that the direct contact between galvannealed coating layer and die is prevented by coating silica-base film, then the adhesion at interface between the coating layer and the die is prevented, which decreases the true contact area between the coating layer and die, and consequently improves the sliding property. (2) The spot weldability evaluated by electrode tip life is improved largely by coating silica-base film, because protective layer which is composed of SiO2 and Fe-Zn alloy is formed on the surface of the electrode tip. (3) The silica-base lubricant film has no effect on phosphatability.
  • Corrosion Property for Solid State Bonded Joint of SUS304L Stainless Steel and Zr

    pp. 405-410

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    Corrosion resistance of diffusion bonded joint with Ta foil inserted between the bonded surfaces and friction welding joint for SUS304L and Zr was examined in 3N-HNO3 solution contained Cr6+ ion.
    In a short term dipping test, it was difficult to qualitatively investigate the corrosion property for both joints, because it depended strongly on the surface condition (preparation) of the specimen before the test. In a long term dipping test, however, the type of the corrosion was mainly found intergranular corrosion in SUS304L base metal for all of the joints, moreover this developed the falling off the crystal grain of SUS304L base metal. In this corrosion process, a possibility that galvanic potential difference between dissimilar metals accelerated corrosion was pointed out, then local potential gradient was investigated using a measuring system, in which a sharp vibrating probe was scanned across the joint interface. SUS304L base metal showed a positive local potential gradient which indicated on acceleration of corrosion in SUS304L. But it was not so large and corrosion rates of SUS304L for the both solid state joining were nearly same value as that without Zr or Ta base metals.
    The acceleration of the corrosion at dissimilar metal joints were not observed from the results of the dipping test and the measurement of the local potential gradient, it is considered that there is no problem of the corrosion resistance in these joints.
  • Development of Aus-drawing Process in Medium Carbon Spring Steel for Coil Springs

    pp. 411-418

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    In order to improve the fatigue strength and the sag resistance in medium carbon spring steels, a novel thermomechanical processing, "aus-drawing", was developed. Aus-drawing is an aus-forming using wire drawing. The aus-drawing process was applied to two kinds of mediumcarbon spring steels containing Si, SWOSC-V, and SAE9254 (JIS SUP12). Three kinds of typical microstructures appeared in the aus-drawn wires depending on the drawing conditions:fully martensite structure, surface bainite structure, and fully bainite structure. It was clarified that mainly the acceleration of bainitic transformation kinetics by increase in plastic strain and additionally the heat generation during drawing cause the appearance of bainite. The preferential formation of bainite near the surface could be explained by the relatively large equivalent strain near the surface due to redundant shear strain during drawing. The aus-drawn wires with fully martensite structure showed superior fatigue strength and sag resistance to those of the conventional oil-tempered wires after tempering and shot peening. On the contrary, the aus-drawn wires with bainite showed inferior properties to that of the conventional wires. Therfore, it is quite important to decrease the redundant shear strain near surface to inhibit the bainitic transformation, in order to succeed the aus-drawing process.
  • Ausformed Bainite in SUP7 Spring Steel

    pp. 419-426

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    In order to clarify the applicability of ausformed bainite in spring wire, effect of ausforming on the microstructure and the hardness of isothermally held JIS-SUP7 spring steel was investigated. The acceleration of isothermal transformation by ausforming was qualitatively confirmed. Ausforming made the pearlite colony size small, but the hardness of proeutectoid ferrite+pearlite structure only slightly increased by deformation. The bainitic ferrite size, especially its thickness, was decreased by ausforming. The bainitic packet which is an unit of bainitic ferrites with the same direction was refined by 20% deformation, while after 30% to 35% deformation the bainitic ferrite within an identical prior-austenite grain tended to align to a same direction so that the packet rather coarsened. Independent of deformation, large amount of austenite up to 35% retained after quenching to room temperature in the specimens tempered at upper bainite region. In the specimens tempered at lower bainite region, the amount of retained austenite largely increased by ausforming. In spite of the increase in retained austenite, ausforming by 30% to 35% strengthened the material tempered at bainite regions. Especially, the ausformed lower bainite showed large hardness of HV650 which is superior to a conventional quenched and tempered material with tempered martensite structure. These results indicate that the ausformed lower bainite could be applied to practical use.

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