A mathematical model was developed for the decomposition of calcium carbonate sphere. This model involves four processes. The first two processes are chemical reaction in the reaction interface and CO2 gas pressure flow in the product layer. The other two precesses are heat transfer between gas and particle by radiation and convection and conduction of heat in the product layer in the heat transfer process. The weight-loss during the decomposition was measured by thermo-balance and variations of temperature were measured at center, surface, and the other points of spherical particle during the decomposition of limestone in CO2 (1 atm) .Applying the measured values to the proposed model, four transport parameters were determined. The distributions of temperature and CO2 pressure in the spherical particle during the decomposition of limestone were predicted by using these parameter for the model, and the rate controlling process was discussed.
Simultaneons injection of oxygen and oil in large quantity is likely to cause slipping and other irregularities in blast furnace, if the choice of each quantity is inappropriate. For this reason, it is necessary to treat this problem quite carefully both from theoretical and operational points of view. To solve this problem the idea of appropriate operational range is introduced, which takes into account the limitation of heat exchange of gas and burden, theoretical temperature at tuyeres and perfect combustion of oil. Fukuyama No 2 BF has been operated by applying these consideration. The operational results of 380 kg/t HN coke ratio and 78 kg/t HM oil ratio have been obtained by the enrichment of oxygen of 25%. The furnace is operated, at present, under good condition with 3.8% oxygen enrichment, which proves that the idea of appropriate operational range is very beneficial in injecting oxygen and oil in large quantity.
Machematical model for determining the transitional variations of process variables which take place during the progress of refining process in the electric arc furnace is developed in this work. In this model, decarburization by CO gas bubbles formed on the surface of the furnace wall, direct oxidations of carbon, silicon and chromium by the injected gas bubbles of oxygen and indirect oxidations of silicon and chromium at the interface between slag and metal have been analysed theoretically. On the basis of the model, numerical calculations relevant to the refining period of electric arc furnace have been conducted under the various operating conditions with the aid of digital computer. The results calculated on the transitional variations of process variables have been compared with the experimental data, and the former has been in good agreement with the latter. Futhermore, the effects of the initial temperature of molten steel and the flow rate of oxygen on the transitional variations of the temperature of molten steel and those of the concentrations of carbon, silicon and chromium in it have been evaluated theoretically by the use of the model.
In this paper an experimental study of the microsegregation and the microstructure in uni-directionally solidified 18Cr-BNi and 25Cr-20Ni austenitic stainless steels is described. The aim of the present investigation is to provide the quantitative data of the microsegregation and the microstructure in alloys of engineering interest in order to explain the homogenization process, and moreover to interpret the mechanism of the solute redistribution in dendritic growth. For this purpose Cr- and Ni-isoconcentration contours around the primary dendrite arm were determined and a discussion was made on the solute distribution as a function of the fraction of solid which was given by area fraction solidified in the transverse section. The results obtained are as follows: 1) Minimum Cr and Ni concentration at the center of primary dendrite stalk is slightly decreased with increasing distance from chill. Consequently with increasing distance from chill, the effective distribution coefficient KE decreased and on the contrary the segregation ratio I increases. 2) There is a inflection in the solute distribution curve drawn against the fraction of solid. Andthe value of the fraction of solid at the inflection point is increased with increasing distance from chill. Therefore, it is concluded that the diffusion layer exists ahead of the solid-liquid interface near the growing dendrite tip, that is, homogenizing in liquid is never caused during dendritic growth, at least in the initial stage, and the diffusion layer has a very remarkable effect upon the solute redistribution.
Effects of alloying elements on the drillability of low carbon steels have beeninvestigated. From the view point of the effects on the drillability of low carbon steels with normalized lamellar pear-lite structures, alloying elements are classified into two groups as follows. (1) Elements represented by chromium which increase the pearlite fraction by lowering eutectoid carbon content and cause little solid solution hardening. (2) Elements represented by phosphorus which have little effect on the pearlite fraction but increase the hardness by solid solution hardening of ferrite. The first group elements largely increase the drillability and the second groupones have little effect on the drillability. These effects of alloying elements on the drillability are understood mainly asthe net results of the benificial effect by decrease of the cutting force due to the contribution of pearlite on stress concentration and a negative effect by increase of the cutting force due to the increase of hardness. The effects of alloying elements on the drillability with spheroidized structures of cold drawn low carbon steels are also discussed with the effects due to decreased stress concentrationby spheroidized pearlite and the effect due to hardness
The influence of melting atmosphere and impurity elements on the hot-workability of Fe-30% Cr alloys has been studied as well as the effect of vacuum-calcium refining on the mechanical properties. The results obtained are as follows. The deformation resistance of zone refined specimens with the lowest impurity content is from 23 to 13 Kg/mm2 in the temperature range of 850° to 1300°. Increasing the interstitial elements such as carbon and nitrogen in the vacuum melted specimen raises the deformation resistance in any hot-working temperature. However, the content of oxygen (up to 0.2%), sulfur (up to 0.1%), manganese (up to 2%), silicon, and aluminium (up to 0.5%) have not any significant effect on the deformation resistance. The specimens of more than 0.017% carbon reveal intercrystalline fracture from above 1200°C. The crack initiations due to the cluster of alumina or chromium oxide inclusion are also observed. It is ascertained that the globular type inclusions found in the vacuum-calcium refined heats consist mainly of calcium aluminate, and their tensile strengths of approximately 45-65Kg/mm2 with elongations of 28-35% are obtained
Recently there are demands to decrease the carbon equivalent of 50 kg/mm2 high tensile strength steels in order to prevent cold cracking of welds on welding with a low temperature preheating or without preheating. The carbon equivalent of 50 kg/mm2 high tensile strength steels was reduced from about 0.40 per cent to below 0.30 per cent. A special heat treatment was applied to a low carbon equivalent steel thus obtained to ensure the tensile strength to be more than 50 Kg/mm2. The steel produced by this method has an excellent notch toughness in addition to the specified high strength because of the extra low carbon content and very fine grain structure. The sensitivity to cold cracking of weld HAZ was examined by the Tekken cracking test, overhead fillet welding cracking test, and so on. No cold cracking was found at all in welding even at such a low temperature as 0°C, and the low carbon equivalent was confirmed effective. The weak point of this low carbon equivalent steel is softening of HAZ when welded by large heat inputs. The tensile strength of weld-joint decreases about 10 per cent in a narrow width specimen. However, the decrease of tensile strength of weld-joint is at most 3 per cent in the wide specimen with the width about 6 to 7 times the plate thickness. It was found that softening could be neglected in almost all the steel structures because they were composed of wide plates.
The transitional probability of particles between two fixed positions was observed in a horizontally rotating cylinder. Orbits of the revolving particles are scarcely disturbed with a stationary rotation of cylinder, whereas cascading paths on the surface region of particle bed are accompanied with probabilities. A special limited zone to particle motion is found, which is named the forbidden region, and its cause is discussed. Calculations of the extent of the region agreed with observations.