Pulverized coal injection (PCI) into a blast furnace causes low permeability in the shaft zone of the blast furnace. It is therefore necessary to optimize the burden distribution which affects gas flow resistance for achieving high injection rate of pulverized coal. The main purpose of this study is to clarify the influence of the burden distribution pattern on the gas flow in a blast furnace experimentally and theoretically. A two-dimensional mathematical model for gas flow was developed based on the Ergun's equation in the packed bed and on the k-ε turbulence model in the freeboard, respectively. The gas flow phenomena in the packed bed were analyzed at different gas velocities for several conditions of the inclination angle of layer, layer number and layer thickness ratio, L_o/L_c.
As a result, the increase of L_o/L_c led to the rapid increase of pressure drop in the L_o/L_c range less than 2.0 under the condition of constant total height of the packed beds. The pressure drop decreases with the increases of the inclination angle and layer number under the fixed height of the packed beds. It could be inferred that the charging pattern of thinner layer is effective to reduce the pressure drop in a blast furnace operating with high PCI rates from the analysis of gas flow in the packed bed without interfacial resistance and fine powder.

View full abstract

In the present investigation an attempt has been made to study the swelling behaviour of iron oxide pellets made from chemically pure iron oxide and natural ore from Bailadila Mines. The tests were conducted under isothermal conditions. The variable parameters studied are reduction temperature, time, partial pressure of H₂ and CO, flow rate, firing temperature, firing time, porosity of pellet and additive like CaO, MgO, SiO₂ and Al₂O₂. The experiments were statistically designed so that the effect of each variable and interactional effect of different variables can be quantitatively assessed. Swelling index of the pellet has been found to be maximum at a critical rate of reduction, which is controlled by reduction temperature, reducing gases, partial pressure and flow rate. Firing temperature and time have been found to affect swelling index of pellet by affecting porosity. Addition of CaO, MgO and SiO₂ has been found to decrease the swelling index of the pellet. The application of the results to practical steel makers has also been discussed.

View full abstract

Using the Knudsen-cell mass-spectrometric technique, coupled with an analysis based on the Gibbs-Duhem integration of mass spectral ion-intensity ratios, activities have been obtained for the molten FeO-MgO-SiO₂ system. The thermodynamic activity of FeO has been dtermined as a function of FeO content (0.1-0.9 mole fraction FeO) across the ternary section defined by an MgO to SiO₂ mole fraction ratio of unity. A significant positive deviation from ideal solution behavior is found for the FeO activity.

View full abstract

A kinetic study has been made on the reduction of iron oxide in molten slag with graphite. The composition of the primary slag was changed so that SiO₂ concentration varied between 0.33 and 0.50 mole fraction, and slag basicity between 1 and 2. The experimental temperature was 1300°C. The reaction rate is significantly affected by the slag composition. From values of the mass transfer coefficient, calculated by using penetration theory, it is presumed that for the slags with basicity of 2, the reaction rate is controlled by mass transfer in the slag phase, but chemical reaction resistance is predominant in slags with lower basicities. By applying a mixed-control model to the latter case, the apparent chemical reaction rate constant was calculated. The rate constant decreases largely with increasing the silica activity. The reaction rate also decreases with the presence of phosphorus in the slag. These behaviors indicate that the reaction rate is very sensitive to the interfacial chemisorption of the surface active agents.

View full abstract

A numberical study was performed for the three-dimensional turbulent fluid flow in the ASEA-SKF ladle. The recirculatory flows are induced by an electromagnetic force field and/or gas injection. The effect of each stirring method and that of combined stirring on the flow characteristics were examined.
Induction stirring was superior to gas stirring for the removal of non-metallic inclusions due to the flow pattern with a less stagnant region. As for the mixing effect, however, gas stirring was more effective than induction stirring. From the numerical results, combined stirring of the induction and gas stirring was suggested, so that it was more effective than each individual stirring method. The numerical results were compared with the data from the field operations, which showed good qualitative agreements.

View full abstract

The spheroidization of cementite at subcritical and intercritical temperatures was studied quantitatively by evaluation of a shape factor for the cementite particles. It was found that the degree of spheroidization, as determined by the values of the shape factor, was markedly accelerated by treatments consisting in either (1) subcritical annealing after cold deformation or (2) intercritical annealing followed by subcritical annealing. Nevertheless, some differences were found among the microstructures resulting from the above treatments, which were related to the mechanisms of cementite formation in each of them. Also, the kinetics of austenitization during intercritical annealing was found to be accelerated by previous deformation, and the analysis of the formation of austenite at intercritical temperatures in terms of an Avrami equation was consistent with an "effective" saturation of ferrite-pearlite boundaries with austenite nuclei, followed by a planar mode of growth into the pearlite nodules.

View full abstract

The crystallographic aspects of zinc and zinc-nickel alloys on steel sheets have been studied by means of transmission electron microscopy (TEM) and the O-lattice theory. TEM observation shows that the pure zinc and zinc-nickel hcp η-phase electrodeposits grow epitaxially on α-iron substrates with the Burgers alignment in keeping with the O-lattice theory, although the dimensions of the a-axis and c-axis vary with the Ni content. For the nickel-rich γ-phase, a cube/cube orientation relationship is observed. The relationship can also be interpreted in terms of the O-lattice theory.

View full abstract

The effects of silicon and manganese contents on volume fraction and stability of retained austenite particles in 0.2C-(1.0-2.5)Si-(1.0-2.5)Mn (mass%) TRIP-aided dual-phase steels were investigated. In addition, the relationships between above retained austenite parameters and ductility at room and moderate temperatures were discussed through studies on strain-induced transformation behavior of retained austenite.
As increasing the silicon and manganese contents except for 2.5 mass% manganese steel, the initial volume fraction of retained austenite increased with accompanied by reducing carbon concentration in retained austenite. It was found that the ductilities of these steels became maximum at a given temperature between 23 and 175°C, i.e., a peak temperature. The peak temperature was concluded to agree well with the temperature at which the strain-induced transformation of retained austenite was suppressed moderately for each steel. Moreover, the peak temperature Tp (°C) was related to estimated martensite-start temperature Ms (°C) of the retained austenite as Tp=3.04Ms+187. Strength-ductility balance, i.e., the product of tensile strength and total elongation, at the peak temperature linearly increased with an increase in the initial volume fraction of retained austenite.

View full abstract

The cold rolling behavior of solidified columnar crystals in a 19% Cr ferritic stainless steel has been investigated in order to clarify the effects of the initial orientation of each columnar grain and of the interaction with adjacent grain in a polycrystalline specimen. The specimen showed {001}<uv0> texture before rolling and {001}<110> texture after 70% rolling reduction. It was clearly shown that the rolled microstructure and the crystal rotation by rolling strongly depend on the initial orientation. The 70% rolled microstructure of (001)[100] oriented grains consisted of a large number of fine stringer deformation bands, whereas (001)[110] oriented grains showed a uniform and non-characteristic deformation structure. In the grains having intermediate orientations such as (001)[510]-[320], stringer deformation bands formed near grain boundaries. Both of the (001)[100] and (001)[110] oriented grains maintained their initial orientations even after 70% rolling reduction, while the (001)[510]-[320] oriented grains rotated toward (001)[110]. It was emphasized that the stability of (001)[100] orineted grains against rolling is contrast to the case of (001)[100] oriented bcc single crystals where the crystal rotation toward (001)<110> occurs. This difference was discussed from a viewpoint of the interaction with adjacent grains.

View full abstract

A mathematical model has been developed that predict the final mechanical properties of hot rolled steels. It consists of submodels for static and metadynamic recrystallisation, grain growth and the transformed ferrite grain size. Each submodel was characterised for a wide range of C-Mn and HSLA steels. The total microstructure model has been integrated into process models and evaluated using production data for plate, structural, bar and strip rolling. Results to date indicate that the accuracy of the model is excellent and is suitable for the evaluation of new steel grades and the development of optimised thermomechanical processing routes.

View full abstract

Compression tests were performed on TiAl crystals containing unidirectionally aligned lamellae based on the function of temperature and the angle (φ) between the loading axis and the lamellar planes in order to determine the effect of lamellar structure on plastic behaviour. For specimens with φ=90°, the yield stress increased anomalously with increasing temperature and reached a maximum peak around 500°C. This phenomenon was particularly noticeable in the specimens containing fine and homogeneously distributed lamellae. Thin α₂ plates in lamellae act as an effective barrier to the motion of dislocations, and the plastic behaviour of <1126>-type dislocations in the α₂ plates may be responsible for the anomalous strengthening. In the cases of φ=45 and 0°, the weak temperature dependence of yield stress was mainly due to the mode of deformation in the γ matrix. Cracks nucleate often at the interface between the α₂ plate and γ matrix and/or at thick α₂ plate. Lack of activation of pyramidal slip in the α₂ plate makes the accommodation of the concentrated stress at the interface more difficult. Addition of vanadium, which is thought to activate the pyramidal slip, was effective in improving the ductility.

View full abstract

Analysis of the superconductor Tl₂Ba₂Ca_nCu_n+1O_x ((22n·n+1)) by X-ray fluorescence spectrometry was studied. Specimens were prepared by the microdroplet analysis method to avoid both the evaporation of a poisonous element (Tl) during fusion (the glass bead technique) and the spread of pressed powder (the briquetting technique) during the measurement in a evacuated spectrometer. The composition was calculated by using the fundamental parameter method to minimize the need for standard specimens. The unknowns and standard specimens were prepared by depositing 0.353 mg/cm² oxides on filters. The deposition amount was adjusted to obtain a high PB ratio and sensitivity, and also to reduce both the influence from the specimen mass thickness and the absorption and enhancement effects. As a result, good analytical accuracies for Tl₂O₃, BaO, CaO, and CuO were obtained as 0.70, 1.06, 0.17, and 0.29 wt% in the case of (2223), and 0.53, 0.73, 0.14, and 0.19 wt% in the case of (2212), respectively.

View full abstract

Various advanced structural composite materials have recently been researched and developed in the field of aeronautics and aerospace technologies. One of the most important and urgent problems is to characterize the damage tolerance behavior of these advanced materials for broad use in primary structural applications. The final goal of this study is to establish new concepts of material design for high performance (high strength, high toughness and high durability) metal matrix composites. In this paper, current R & D trends of advanced structural composite materials in Japan were first outlined. Secondly, some of the author's current research projects, especially fracture mechanics of discontinuous and continuous fiber reinforced metal matrix composites were briefly introduced relating to the testing and evaluation of damage tolerance behavior. Some technical problems were also discussed in the development and standardization of fracture mechanics testing and evaluation methods. Finally, the current status of testing and evaluation of metal matrix composites was introduced by reporting on the round robin test (RRT) done for pre-standardization.

View full abstract