An accumulation of coke fine in blast furnace which caused by an operation with pulverized coal injection, makes decrease of air permeability in the furnace. One of the factors of this problem is that coke particles are impacting each other and coke fine generates in the raceway. However, it is so high temperature and pressure in raceway that it is very difficult to admeasure various parameters of coke grinding phenomenon. Therefore, a numerical model for estimation of grinding rate is required. We developed a numerical model for estimation of the grinding rate using result of both analysis of gypsum particles behavior and grinding experiment with gypsum particles. The model is based on grinding energy calculated by combining measured grinding rate of gypsum particles in a rotational drum with analyzed data of behavior of the particles. Additionally, we examine the validity of the numerical model to apply to a spouted bed. Thereby we verified qualitative validity of the model.
A new method of deoxidation of molten iron has been developed with magnesium vapour produced in-situ by carbothermic reduction of magnesia. Pellets of magnesia and carbon powders were charged into an alumina porous tube, which was immersed into the iron melt. The tube had one hole of lmm in diameter, through which Mg vapour and CO gas produced by the carbothermic reduction of MgO were injected into the melt together with Ar carrier gas. The partial pressure of Mg vapour in the injected gas bubble changed with pellet mass, temperature and Ar carrier gas flow rate. The deoxidation rate increased with increasing pellet mass and temperature. The deoxidation product MgO floated up to the free melt surface with the bubble and also reacted with Al2O3 of the immersion tube. The reoxidation reaction of Mg vapour by CO gas in the bubble occurred and the deoxidation efficiency of Mg decreased to some extent. A mathematical kinetic model of the deoxidation with Mg vapour was constructed. The amount of oxygen reacted with Mg is greater during the bubble formation period than during the bubble ascent period. At higher oxygen concentration, the overall deoxidation rate is controlled by the Mg vapour supply; i.e., the rate of carbothermic reduction of magnesia, while at lower oxygen concentration by the mass transfers of Mg vapour in the bubble and oxygen in the melt.
The oxidation rates of phosphorus in high carbon iron melts were examined at 1 400°C by using CaO-based slags such as LD slag and Calcium Ferrite (CF) type slag. The results were analyzed with the coupled reaction model. Although, little phosphorus was initially oxidized by the addition of LD slag alone, the degree of dephosphorization was considerably improved by adding further FeO to LD slag. This improvement can be explained by the increase in oxygen activity at the slag-metal interface and mass transfer coefficient. The degree of dephosphorization by CF type slags was higher than that by LD slag. Among them, the degree of the dephosphorization by a mixture of CaO or CaCO3 and Fe2O3 was higher than that by CF sintered. The phosphorus distribution ratio and the CaO efficiency for dephosphorization by CF type slags were compared with those by slags containing CaF2 or CaCl2. As a result (or As a conclusion) it was expected for CF type slags to be the effective flux for the dephosphorization in practical operation.
The fatigue property under internal pressure is the most important property for high-pressure cylinders. Generally, this property is nearly proportional to the tensile strength of the tube so far as the tube is free from material defects and welding defects. However, this property is affected by the residual stress. In the production for high-pressure cylinders, drawing is the most widely employed practice as it ensures high dimensional accuracy and permits the production of tubes of intermediate sizes. In this method, however, the fatigue property is decreased because of the generation of tensile residual stress. To eliminate this tensile residual stress, a method of pipe expansion with drawing by the use of two-stage plug has been developed. This method ensures the compressive residual stress on a stable basis and improves the fatigue limit under internal pressure. As a result, the fatigue limit improved 17% under the conditions of reducing the outside diameter by 10% and the wall thickness by 32.7%, respectively, with 0.5% pipe expansion.
Tensile flow stress of an ultra low carbon steel was investigated at temperatures between 77K and 293K with strain rates from 2×10-2/s to 2×103/s. Stress-strain curves were described by using the Kocks-Mecking model in which several parameters were determined from the experimental data obtained by conventional tensile tests with lower strain rates less than 2×100/s. It is found that the flow stress at 2×103/s estimated by the Kocks-Mecking model agrees well with the stress measured by Hopkinson-bar method. The decrease in work-hardening rate at 2×103/s was discussed from the viewpoints of temperature rise and microstructural evolution during high speed tensile deformation, leading to a conclusion that the former was a main reason.
The Tatara is the traditional iron-and steelmaking process in Japan. The box type furnace is about 1 m width, 3 m length and 1.2 m height. The process produces steel bloom and pig iron from iron sand and charcoal. The furnace is built on the charcoal bed in a big underground construction which is separated into upper and lower parts by a thick clay layer, "Kobune Kawara". The lower part is a drainage. The upper part has a charcoal bed, "Hondoko", with twin caves, "Kobune", on the both sides. The "Kobune" keeps its temperature lower than 41°C and humidity higher than 89%, that is, 4.8×10-2kg·m-3 in terms of water vapor concentration, during "Tatara" operations. The heat flow and temperature distribution around the furnace during operation was numerically simulated. The water vapor in "Hondoko", hearth and "Doi" flows to "Kobune" according to heat flow and disperses to the surroundings. Further the historical development of underground construction is discussed.
Stellite type alloys have been utilized as weld hard overlaying alloys for valves used in high temperature and high pressure water. However, overlaying alloys free from cobalt contents have been ardently hoped for because cobalt is one of the main elements to increase radioactivity levels in radiation environment. The present investigation reports development of cobalt-free overlaying alloys based on the composition of high manganese steel with varying contents of nitrogen and molybdenum for these applications. Wear tests are conducted at 573K which will be the use temperature of the alloys, and the most resistant alloy is found to be resistant as high as 2.5 times to the stellite type alloys. Galling tests are also conducted at 573K with the most wear resistant alloy, and the alloy is found to be scuffing resistant as high as 7 times to the currently applied stellite type alloys. Thus, the developed alloy is found to be recommended as a cobalt-free overlaying alloy for valves of used in high temperature and high pressure water. The alloy is a χ-phase strengthened alloy, and utilizes a different strengthening mechanism from currently utilized mechanisms such as carbide strengthening and Laves phase strengthening mechanisms. Actual application procedures of the alloys are under investigation at present as the next step of the development.