Dissolution rates of sintered alumina into molten CaO-SiO2-9mass%Al2O3-10mass%MgO slags were measured by rotating specimen method. Experiments were conducted at various revolution speeds, temperatures, and CaO/SiO2 ratioes, and the microstructures of specimens after experiments were examined by EPMA. Based on these results, the dissolution mechanism was discussed. The dissolution rate of alumina increased with increasing revolution speed and rising temperature. These results suggested that the dissolution rate was controlled by mass transport in the boundary layer of molten slags. The dissolution rate of alumina decreased rapidly as increasing CaO/SiO2 from 0.64 to 0.80, and then increased rapidly as increasing CaO/SiO2 from 0.80 to 1.00. According to the EPMA analysis, a compact deposition of MgO·Al2O3 spinel particles in slag and a formation of CaO·6Al2O3 compounds in alumina were confirmed in the specimen immersed into the slag of CaO/SiO2=0.80. It was estimated that these reaction proudcts suppressed the flow of slag components to decrease the dissolution rate. However, MgO·Al2O3 spinel particles observed in the specimen immersed into other slags were scattered, and might not disturb the flow of slag component, so that the dissolution rate was not retarded.
The deoxidation equilibrium of aluminum in liquid nickel saturated with solid alumina has been measured at the temperature ranging from 1823 K to 1973 K using the sampling technique with a view to understanding the equilibrium between aluminum and oxygen in liquid nickel. The temperature dependence of the equilibrium constant for the deoxidation reaction was presented to be : log KAl(Ni)(=log a2Al·a3o/aAl2O3)=-28770/T+1.67 18231973 K while the deoxidation product, log K'Al(Ni)(=log[%Al]2 [%0]3), was expressed as follows : log K'Al(Ni)=log KAl(Ni) + 1.47(3[%Al]+3.4[%0]) Al<1.1 mass %, 18231973 K The deoxidation of liquid nickel-iron binary alloys with aluminum was measured up to 50 mass pct iron. The activity coefficients of aluminum and oxygen in nickel-iron alloys based on pure liquid nickel were estimated by the following equation : log fFeO(Ni)+2/3log fFeAl(Ni) =-0.028[%Fe] up to around 10 mass pct iron at 1923 K.
Calcium ferrite is very important for improving the properties of strength and reducibility of sinter. But the formation mechanism of binary calcium ferrite under the stable condition of CaO·2Fe2O3 was not studied sufficiently. Therefore, as fundamental study of calcium ferrite formation, the mechanism of calcium ferrite formation in solid state reactions between CaO and Fe2O3 at 1190°C in air was investigated by using the diffusion-couple method. The results are summarized as follows. (1) The reaction between CaO and Fe2O3 starts at the CaO/Fe2O3 interface to form CaO·Fe2O3. After a short initial period, three kinds of calcium ferrites, 2CaO·Fe2O3 (C2F), CaO·Fe2O3 (CF), and CaO·2Fe2O3 (CF2) grow in that order from CaO layer toward Fe2O3 layer. (2) The formation rates of C2F, CF and CF2 are controlled by the diffusion of Ca2+ and Fe3+ in each layer. (3) The C2F forms at the interfaces of CaO/C2F and C2F/CF, but the formation rate at the CaO/C2F interface islarger than that at the C2F/CF interface. The CF forms at the CF/CF2 interface, and grows toward CF2 phase except for the beginning of the reaction. The CF2 forms at the CF2/Fe2O3 interface, and grows toward Fe2O3 phase. The thickness of each layer of calcium ferrites increaces with the progress of reaction time.
The technology for granulating coke breeze by centrifugal rolling type pelletizer, which is operated at a Froude number (Fr) 102 times more than an ordinary drum mixer, and the effect of granulated coke breeze on sintering operation, granulation of raw mix and quality of sinter were quantitatively studied by use of sinter pot and NAGOYA No.2 sinter plant. The following results were obtained : (1) In the granulation test of coke breeze, the centrifugal rolling type pelletizer can not only granulate fine coke breeze but also penetrate ultra fine coke particles into a coarser coke, while preventing the granulated particles from becoming excessively coarse. (2) In the pot test and the sinter plant test, it was clarified that granulated coke breeze becomes the nucleus in quasi-particles of raw mix and then promotes the granulation of other raw materials in the sintering process of iron ores. In addition, this new technology was confirmed to be able to decrease the NOχ emission by reducing the fine portion in coke breeze. The addition of quick lime reduces the NOχ emissions further. It was also clarified that the reducibility of sinter was improved.
The relationship between the equilibrium compositions of Fe-Ti-Mn melts and those of coexisting oxides has been investigated by employing a cold crucible at 1873K. The oxygen content was shown to decrease with increasing the contents of manganese and titanium, the effect of the latter being significant. The metals which had the same contents of manganese, regardless of their titanium contents, were equilibrated with molten oxides having a constant activity ratio of MnO and FetO. Using the metal compositions and Gibbs energies of the formation of component oxides, iso-activity contours of MnO, FetO and TiO1.5 for the MnO-FetO-TiO1.5 melts at 1873K were evaluated. The optimal conditions for practical deoxidation processes with Ti-Mn alloys are discussed.
The solid-liquid two phase flow influences on the properties of materials such as the semi-solid metals or the particulate-reinforced metal matrix composites. Therefore the flow phenomena of water-polystyrene mixture with high fraction solid in a suddenly enlarged cavity were examined. The mixture in an airtight vessel was ejected vertically into the cavity by increasing the internal pressure of the vessel. The shape of free surface of the mixture became more stable with increasing fraction solid. The main reason of suppressing the disturbance of the free surface is not the increase of the mean relative viscosity but the increase of fraction solid of the region near the free surface. The concentration of particles decreased at the center of rotary motion in the early stages of filling and at the boundary between the rising particles and the piled-up particles, which existed above filling ingate. It was the inertial force of particles that held the low-concentration region at the center of rotation. The low-concentration region above the ingate is caused by the collision of particles.
When surface cracks on continuous casted slab were observed by a microscope, internal oxidation layers were sometimes present along the cracks. These layers that were called subscales were paid attention. The subscale was formed in steam atmosphere in laboratory for considering of the generated mechanism of the surface crack. The results are summarized as follows, (1) The subscale was the internal oxidation layer where the generated rate of scale was greatly reduced. (2) The thickness of the subscale depended on the temperature and the time, and that was calculated by the internal oxidation theory. (3) The type and the diameter of particles in the subscale also depended on the temperature. (4) Therefore, the surface crack formed temperature and position in the continuous caster were able to decide by the observation of the subscale.
In order to elucidate the formation of solidification structure in twin roll process, experiments of the strip casting of SUS304 austenitic stainless steel were done by using a laboratory scale twin roll caster. In the cast strips, there exist two kinds of solidification structures ; columnar dendrite and equiaxed crystal zones. With increasing contact time between roll and metal, the thickness of dendritic zone increases, while that of equiaxed zone is kept almost constant. With increasing initial roll gap, only the equiaxed zone is enlarged. Furthermore, effects of the superheat of molten steel and the roll supporting force on the formation of solidification structure have been made clear. The dendritic zone is formed when the solidifying shells are contacting with rolls. On the basis of the experimental results and theoretical analysis of heat transfer in the strip, it has been deduced that, under the conditions of relatively high superheat of molten metal and low roll supporting force, the equiaxed zone results from the preferential growth of free crystals ahead of the dendritic solidification front, with the abrupt decrease in the heat transfer coefficient on strip surface after the strip goes away from rolls.
The effect of rolls made of various tool steels on the lubrication characteristics are examined by rolling annealed low carbon steels by means of the simulation testing machine developed by one of the authors. The lubricity is evaluated by measuring the coefficient of friction for each test and the antiseizure property of rolls is evaluated by the observation of surfaces of rolled workpieces and rolls which are rolled under various conditions of rolling speed and reduction in thickness. The experimental results on the anti-seizure property are discussed based on the calculation of temperature at the interface between roll and workpiece and based on the observation of appearance of friction pick up on surface of rolls. The conclusion obtained are as follows ; (1) The difference of coefficient of friction among roll materials is small. (2) Anti-seizure property depends on the carbide content of roll material and it can be quantitatively evaluated by the calculated interfacial temperature. (3) Carbides on roll surface are effective for friction pick up.
The effect of Al content in the Zn bath on the unevenness of the coated surface of galvannealed steel sheet was investigated by observing the growth of the Zn-Fe alloy during galvannealing process. In the case of 0.13 mass% Al, Zn-Fe alloy initiated homogeneously on the substrate surface grows uniformly during galvannealing and this results in an even coated surface. In contrast, with a high Al content (≥0.17 mass%), Zn-Fe alloy initiates preferentially at the substrate grain boundary at an early stage of galvannealing and this brings about the formation of an outburst structure. As galvannealing progresses, this structure predominantly grows outwards by withdrawing the surrounding molten zinc. The coated surface, thereby, turns out to be uneven. An increase in the unevenness of coated surface increases the coefficient of friction and the exfoliation resistance deteriorates when the sheet undergoes the sliding action with ironing.
Organic composite coated steel sheets have been widely adopted by automobile and appliance manufacturers. Silica is usually used for organic composite coatings due to its advantages with regard to corrosion resistance. Although a number of reports have appeared on the mechanism of corrosion control by silica recently, its function in organic composite coating is not yet well understood. In this study, the influence of corrosion test conditions on the corrosion protection effect of silica was studied by exposing organic composite with silica coated electrogalvanized and Zn-Ni plated steel sheets in a cyclic corrosion test, salt spray test and humidity cabinet test. The influence of silica on the formation of zinc hydroxide was also studied by the potentiometric titration of zinc chloride solution with silica. The results indicate that silica accelerates the formation of zinc hydroxide chloride during the corrosion process, and corrosion is controlled as a result of the controlled reduction of oxygen by the zinc hydroxide chloride. Moreover, silica which dissolves during the corrosion process produces stable zinc silicate, and the zinc silicate acts as a barrier to control corrosion.
In order to clarify the mechanism of extensive segregation observed in modified, super clean CrMoV steel forgings for power industry applications ; the effect of such elements as Mn, Ni, Cr and Mo on segregations were studied ; using 8 ton sand mold ingots and unidirectionally solidified experimental ingots. As the result, it was found that heavy carbon segregations and "A" segregations with opposite inclining angle in Mo rich and Mn, Ni poor steels formed by the sinking of markedly segregated heavy liquid because of small partition coefficient and heavy density due to high δ solidification ratio. Therefore, chemistry and ingot shape design have been developed and applied to actual ingots, resulting in relatively small segregations.