The dense wustite plates containing MgO with SiO2 or Al2O3 were reduced isothermally in H2 gas stream over a temperature range of 670 to 930°C. By the presence of very small of SiO2 dissolved in wusuite phase the reduction reaction was promoted at temperatures above 800°C and retarded at temperatures below 730°C. MgO dissolved in FeO with SiO2 cancels the effect of SiO2 mentioned above. Al2O3 dissolved in wustite slows down the reduction in initial stage greatly and that in and after middle stage further more. MgO dissolved in wustite with Al2O3 slows down the reduction in the initial stage further. Correspondence between reduction rate and structure of reduced iron recognized in this work is same as that in previous works.
The applicability of the reduction model proposed in the previous paper (Tetsu-to-Hagané, 73 (1987), p. 972), in which the water-gas shift reaction and multi-component gas diffusion were taken into account, to the reduction kinetics of wustite pellets with H2-CO-CO2 and H2-CO2 gas mixtures was examined. The gas composition was such that the reduction was possible to take place not with CO-CO2 but only with H2. In the calculation, the parameters included in the model were modified depending on the gas composition by using the method proposed in the previous paper. The following results were obtained; 1) The reduction curves calculated by the model agreed well with the observed data except the case of lower H2 concentration. 2) The effect of the water-gas shift reaction was not so significant on the reduction curves, but it was remarkable on the mass transfer rate of each component of gas mixture. 3) Depending on the reduction condition, especially at higher H2 concentration, CO/CO2 ratio in the pellet increased because of the water-gas shift reaction. As a result, the reduction of wustite with CO took place instead of the oxidation of reduced iron with CO2.
Velocity and turbulence around a sphere made of synthetic resin submerged in water and bubbling jets in a cylindrical vessel with bottom blowing were measured by making use of LDV. The melting process of an ice sphere was recorded by video camera. The local Nusselt number Nuθ of the ice sphere was determined from the initial change of the local radius. The mean Nusselt number Nu was calculated from Nuθ by numerical integration over the surface of the sphere. The effects of velocity and turbulence intensity on Nuθ and Nu were investigated. An empirical expression for Nu was proposed as a function of Reynolds number and turbulence intensity. A method of predicting the complete melting time of an ice sphere was presented.
Reduction rate of TiO2 in CaO-SiO2-Al2O3-TiO2 slags by carbon dissolved in iron melts was investigated at 1 350°C 1 600°C under argon atmosphere. It was found that the reduction of TiO2 proceeded simultaneusly with the reduction of SiO2 and was promoted by the addition of silicon to the initial iron melts. For acid slags, the reduction rate of TiO2 decreased with inceasing ratio of CaO/SiO2, whereas it slightly increased for slags with CaO/SiO2>1. The kinetic analysis on the basis of the two film theory showed that the overall rate of transfer of Ti from slag to metal phases was controlled by the rate of chemical reactions at the interface for cases without silicon addition, but it was found that the resistance to transfer of TiO2 in the diffusion boundary layer at slag could not be neglected when some amount of silicon was added to the metal.
For the computer control of steelmaking process in electric arc furnace, a simplified mathematical model suitable for online application has been developed on the following procedure. (1) An equation for judging the meltdown of scrap accurately by monitoring the position of electrodes and the furnace wall temperature throughout the melting stage has been developed. (2) Equations for estimating decarburization and temperature increase in consideration of the decarburizing characteristics in oxygen blowing period, and equations for estimating molten steel temperature change and composition change in the period of temperature adjustment and tapping on the basis of heat and material balances have been developed. (3) Based on these equations in the refining stage, the authors have developed control models calculating the amount of blown oxygen, electric power and ferroalloys requisite for the operation. At EAF shop in Osaka Steel Works, the models are in use for the computer control and contribute to the reduction of power consumption and so on.
For the improvement of surface quality of continuously cast steel, an analysis model taking into consideration of steel casting has been developed on the following procedure in order to explain initial solidification phenomenon in the vicinity of meniscus. (1) A calculation method of temperature distribution has been worked out, assuming that a small quantity of new molten steel flows into mold intermittently and solidified shell and molten steel are casted vertically to the horizontal direction. (2) Direct difference method using inner nodal point is applied to the numerical calculation of heat transfer equation so that the movement of molten steel due to casting can be easily dealt with, and four kinds of equations are made according to the boundary condition as the fundamental equations in divided mesh. By using this model, it becomes possible to estimate the temperature distribution in steady-state under casting. In this study, the solidified shell, slag rim shape and the temperature distribution in mold area in the case of using the ordinary copper mold are estimated. Furthermore the adiabatic effect in the case of using mild cooling mold containing refractory is evaluated quantitatively.
Recently, the demand of customers for the flatness of cold strip becomes more and more strict. Therefore the effective shape correction device has been desired in a shear line for replacement of a conventional roller leveller. Introducing tension leveller on the upstream of a shear line is probably a reliable answer, but its investment cost is large and extra space is necessary. To solve this problem a new type of compact combination leveller was designed based on the theoretical analysis and experiments. This consisted of non-drive stretch leveller, main leveller and double pinch rolls. Then it was introduced in a shear line. Using this combination leveller, the strip is elongated by repeated bending under superposed tension of pay off reel tension and idle leveller drawing force. Friction force of main leveller and pinch rolls causes this drawing force. The strip of satisfactory flatness almost the same as that by tension leveller can be obtained. This new shear line was first constructed in 1986 and has been working successfully. Now the same type combination levellers are under designing and construction.
In the Gatorizing process, extrusion is needed to obtain a fine recrystallized structure. Because of the bottle-neck of the extrusion, however, a largesized disks have not yet been formed. Therefore, it is desirable to develop a new work processing excluding extrusion and applicable to form large disks. In the present study, it was discussed whether the application of superplastic warm-die and pack forging to Ni-base superalloy Mod. IN-100 atomized powder is appropriate or not. Namely, billets, which were a cylindrical case made of carbon steel or austenitic stainless steel and packed with the powder, were heated to 1 100°C and then superplastically forged at a strain rate of 1.8 × 10 -2 s -1 using dies made of Inconel 713C and pre-heated at about 600°C. A desirable forming was performed using a thick walled case made of austenitic stainless steel.
The effects of cold-rolling on strength and toughness at 4K were investigated for a high manganese steel, 32Mn-7Cr steel. The yield strength at 4K was 1118MPa for the unrolled steel and was increased to 1379MPa and 1786MPa for the 20 and 40% cold-rolled steels, respectively. However, the elongation and the reduction of area were decreased with an increase in reduction ratio. Especially, the elongation was significantly decreased. The Charpy absorbed energy and the fracture toughness were also decreased markedly. The decrease in toughness by cold-rolling was due to the formation of subcrack and "flat brittle facet" in the fractured surface. The subcrack was caused by intergranular failure, and the flat brittle facet is believed to be produced mainly by intergranular failure and partly by twin boundary failure.
The effect of microstructure on fracture toughness of near α titanium alloy Ti-6Al-2Sn-4Zr-2Mo was investigated by Acoustic Emission three dimensional location, Acoustic Emission source characterization and fractography method. The fracture toughness of alloy with acicular α structure was superior to that of alloy with equiaxed α structure at the same yield strength level. It was considered that the result was based on the number of large amplitude Acoustic Emission events prior to KIC and on the deflection of the crack path. The large amplitude Acoustic Emission events coresponded to microcracks of 50-80μm which nucleated at the pre-fatigue crack tip along crack front in both structures. Macroscopic crack growth occured where these microcracks coalesced in the direction to specimen thickness. These microcracks lower the stress concentration at the crack tip. Thus it was concluded that microcrackings enhanced the fracture toughness of titanium alloy with acicular α structure.
The metallurgical structure and wear resistance of TiN film formed on 1%C-5%Cr roll steel specimens by Ti vapor deposition with N ions implantation were studied. The main results obtained are as follows: 1) The color of film varies depending on the evaporation rate of Ti and the electric current density of N ions. 2) The X-ray photoelectron spectroscopic (XPS) investigation detected TiN in the golden film and metallic Ti and TiO2 in the silver film. 3) Measurements using a scanning electron microscope (SEM) with energy dispersive X-ray indicated that the concentration of Ti and Fe varies over the distance of a few hundred nm in the boundary zone between the base metal and the coated film. 4) The adhesion of golden film is better than that of silver one. 5) The two-cylinder-type wear resistance test results showed that the golden TiN film significantly improves wear resistance of 1%C-5%Cr roll steel.
Creep tests were conducted on Ni-base heat-resistant alloys Hastelloy XR and XR-II, i. e. versions of Hastelloy X modified for nuclear applications, at 950°C using four types of helium environment with different impurity compositions, and mainly the effect of carburization was examined. For all the materials tested, the values of creep rupture time obtained under the carburizing conditions were similar to or longer than those in the commonly used, standard test environment (JAERI Type B helium). The difference among the results was interpreted by the counterbalancing effects of the strengthening due to carburization and possible weakening caused under very low oxidizing potential. In the corrosion monitoring specimens pronounced carbon pick-up was observed in the environment with high carbon activity and very low oxidizing potential. Based on the results obtained in the present and the previous works, it is suggested that a moderate control of the impurity chemistry is important rather than simple purification of the coolant in protecting the material from the environment-enhanced degradation. Either condition with high or low extremes in the oxidizing and carburizing potentials may cause enhanced degradation and thus are desirable to be avoided at the elevated temperatures.
A new nickle-base single crystal superslloy was developed by applying an "alloy designing" method, which was originated by Watanabe and improved by a group of the National Research Institute of Metals (NRIM). The typical composition range was 6-7 %Cr, 5-6 %Al, 5-8 %W, 5-8 %Ta and 4-6 %Mo (mass%). This alloy had more stable microstructure and higher creep rupture strength than single crystal superalloys so far developed. The basic flow of the designing was as follows. First, the composition of γ and γ' phases and the volume fraction of γ'phase were determined according to the NRIM scheme varying the combination of molar percentages of tungsten, tantalum and molybdenum included in γ' phase. Second, the most desirable combination of γ and γ' couples were selected to maximize the summed values of γ and γ' lattice constants and minimize the misfit between γ and γ' phases. Third, the stability of γ phase during solution heat treatment was assesed by introducing a new parameter of "Solubility Limit Index", whose value was defined by the solubility of included elements into nickel matrix.
Auger electron microscopic analyses were performed to clarify the grain boundary segregation behavior of phosphorus and carbon in the austenitic region of steel. Grain boundary migration during grain growth and recrystallization gave rise to non-equilibrium segregation which resulted in a higher solute concentration on grain boundaries than that of equilibrium segregation. The increment of segregation caused by migration depended on the boundary migration velocity. Faster migration brought about greater concentrations for velocities less than a critical value, which depended on the diffusivity of solute. In recrystallization, faster diffusing elements such as carbon segregated with higher concentrations. It was suggested that the solute sweep effect during grain boundary migration caused the non-equilibrium segregation.