This study deals with the mechanism of small-body-falling namely the vortex-body interaction. The body is regarded as a model for nonmetallic inclusions moving or floating in molten steel. In the study visualization experiments for the motion of a small thin disk falling down in water have been conducted. The motion of the thin disk and its surrounding water velocity field were simultaneously measured using the MOFIA system. The velocity field around the disk was measured by particle image velocimetry (PIV). Fluorescent tracer particles with an average diameter of 10μm were used to separate the wavelengths from both that of YAG laser and those of lights for images taken by a CCD camera. The three dimensional motion of the disk was reconstructed using the images of two high-speed cameras. The experimental results collectively show that the motion of the disk was affected by its density and thickness. The motion changed from two-dimensional zigzag motion to spiral motion with an increase in the density of disk. In the case of a high density disk, a chaotic motion was observed.
Solid CaO and FeOx-CaO-SiO2-P2O5 slag were reacted for 2 to 2400 s at 1573K. The interface of CaO and slag was observed and analyzed by SEM/EDS. The CaO-FeO layer was formed beside solid CaO. The thickness of the CaO-FeO layer increased with time. Next to the CaO-FeO layer, 2CaO·SiO2 phase was formed in the melt and high content of FeO was included in the liquid. The activities of FeO and CaO for each phase were evaluated and reaction mechanism between solid CaO and FeOx-CaO-SiO2-P2O5 slag was discussed. The activity of FeO for 2CaO·SiO2 saturated melt is larger than that for the CaO-FeO layer, therefore, Fe2+ diffuses from slag phase to solid CaO. Then the CaO-FeO layer is formed beside solid CaO. The pass of the slag composition change accompanied by CaO dissolution are represented in the phase diagram for the FeOx-CaO-(SiO2+P2O5) pseudo ternary system.
The film, which is formed by mold flux in the continuous casting mold, plays very important roles in terms of lubrication or heat transfer.But, thickness or structure of it has not been adequately clarified. In this study, it was tried to take the sample of actual flux film from the continuous casting mold just after the cast, keeping its position as it was during the cast. Thanks to this trial, thickness of the flux film at the meniscus in the mold could be clarified. According to the observation on the flux film section by microscope, the structure of the flux film was discussed, in terms of its crystallization. Furthermore, based on the results of the observation mentioned above, the heat transfer phenomenon through the flux film in the mold was discussed. As a result of the discussions, the following conclusions were obtained. 1) The mold flux film can be considered to be about 1 mm. Glassy layer, which has been considered to be molten flux on the top of molten steel during the cast and covered the film just after the cast, can be supposed to make up the film during the cast. 2) The liquid layer in the film is as thick as that is estimated on the basis of mold flux consumption during the cast. 3) In the case that the film at the meniscus in the mold is about 1 mm thick, total thermal resistance of radiation and conduction is equivalent to interfacial thermal resistance between the film and the mold. 4) The reported values of interfacial thermal resistance can be considered to be larger than that in the actual mold during the casting. The reason seems to be that they were measured in the condition without any pressure by the molten steel, like that in the mold. In the actual mold, the interfacial thermal resistance seems to be smaller.
The shape change of longitudinal surface micro-defects in flat rolling was investigated using a rigid-plastic finite element analysis. Rolling of plate with V-shaped scratches or rectangle defects that are parallel to the rolling direction, was simulated assuming a generalized plane strain condition. The calculated results were verified with experiments of model material, and good agreement between both results was obtained. The influence of rolling conditions, such as reduction, friction coefficient and the position of initial defect, on the shape of existing defect after rolling was evaluated. Using the developed FEM, the evolution of seam defects was also simulated, and good agreement with experimental results were obtained. The proposed prediction method can be utilized to make defect free products in flat rolling.
Cathodic protection distance at the shear cut edge of zinc coated steel sheet is an important parameter for the lifetime of the steel material. However, cathodic protection distance is variable for electrolyte thickness, electric conductivity and so on. It is difficult to quantify the cathodic protection distance under various environmental conditions. So it is useful to estimate the cathodic protection distance by numerical analysis. Most of numerical analysis models for galvanic corrosion use a polarization curve measured in a bulk electrolyte solution. However, under thin layer electrolytes, the cathodic current density strongly depends on the electrolyte thickness and the polarization curve shifts by salt concentration. So we developed the numerical analysis model that the polarization curve is calculated by the electrolyte thickness and NaCl concentration. We investigated the cathodic protection distance in NaCl solution for several thicknesses and concentrations by numerical analysis. Moreover, we estimated the cathodic protection distance in the drying process of NaCl solution on the shear cut edge of zinc coated steel sheet.
In order to develop the accuracy of cross cut test, some factors were investigated. Cellophane tape is widlely used in the cross cut test. It was found that the conditions of taping up, the peeling rate and angale must be accordance with JIS. While the temperature and humidity specifications during testing are described in JIS, a great care is required for storage, since the humindity has a strong influence on the performance of the pressure sensitive adhesives during storage as well as upon the results of a peel-off test. The fast rewinding rate from a reel of pressure sensitive adhesive tapes seem to make a rough surface. It must be noted these factors. The cellophase tape showed almost the same peel adhesion for various coated steel plates with different base and post coatings. Therefore, it was clarified that the cellophane tape is suitable for the cross cut test. The trench introduced by a cutter knife on the coated steel plate was observed by a laser microscope. In order to form the stable trench, it was found to be useful in accordance with JIS regulations except the blade angle at the trench introduction.
In order to make sure the great potential of steelmaking slag as a new phosphorus resource, domestic phosphorus material flow in Japan including iron and steel industry has been investigated based on the statistical data on 2002. It has been demonstrated that phosphorus in the steelmaking slag is almost equivalent with that in the imported phosphate rock in the view points of the amount and the concentration. Phosphorus exists mainly in the form of calcium-phosphate or its solid solution with calcium-silicate rather than the FetO rich liquid phase in the slag and exhibits remarkable segregation in the solidified slag. If the strong magnetic field is applied to the crushed slag, precipitated calcium-phosphate solution phase can be separated from FetO matrix phase due to the large difference of each magnetic property. It has also been indicated by the Waste Input-Output model that the phosphorus recovery from steelmaking slag by the new process proposed in the present work has great environmental and economical benefits.