Effect of Oxygen on the Formation of Spheroidal Graphite in Cast Iron

In the cast iron melt the oxygen is present not only as dissolved gas but also as oxide ; it is therefore very important to examine the behaviour of oxides in the melt. The investigation of the Ni-C alloy showed that the oxides SiO_2 or Al_2O_3 cause the precipitation of graphite in lamellar form. The thermodynamic study of the formation of SiO_2 on melting and solidification of cast iron was carried out. Hence it followed that for the production of spheroidal graphite cast iron it is advantageous to melt the metal with low silicon content together with carbon and to increase the silicon content in the melt at elevated temperature. By experimental results obtained on cast iron melted in vacuum where the formation of SiO_2 is smaller it was determined that the spheroidal graphite cannot be practically formed before the inoculation with ferro-silicon. On basis of all results an experiment was carried out for the practical production of cast iron with spheroidal graphite in a basic arc furnace of 50 kg and it was found that the spheroidal graphite cast iron can be produced by inoculation with ferro-silicon

On the Structural Diagram of Cast Iron

The method for expressing the structural diagram of cast iron was studied and a new standard diagram was determined. From this diagram we can know (1) the ranges of structure of cast iron with various components and sectional sizes, (2) a stable range of pearlitic structure and (3) the difference between the effect of carbon and that of silicon on the structure. Comparing the results with Greiner-Klingenstein\u27s and Sipp\u27s data, the writer made clear that the total sum of carbon and silicon (C+Si) and the saturation degree of carbon (Sc) are undesirable as the unit to express carbon and silicon contents in the structural diagram of cast iron

Studies on Pyrrhotite. I : Combustibility of Pyrrhotite

In order to obtain a precise understanding of the combustibility of pyrrhotite, the roasting reaction rates and the relations between the roasting reactions and the roasting temperatures were investigated. It was found that pyrrhotite had a fairly low combustibility resulting from the low ignitibility, the slow reaction rate of oxide formation and the occurrence of the reaction of sulphate formation. The combustibility decreased with the increasing fineness of the ore particle. With increasing flow rate of air, the reaction rate of oxide formation increased, whereas the ignitibility decreased and, so, we cannot admit of any hasty decision whether the combustibility is improved by rapid air flow

Studies on Pyrrhotite. III : Sintering of Pyrrhotite Cinder

The progress of sintering of pyrrhotite cinder during the process of roasting was studied by measuring the resistance of cinder to the penetration of a slender rod. The results showed that pyrrhotite cinder, in general, began to sinter at 250-350℃ with a very high resistance to the penetration of a rod. The sulfate formed below 550℃, and the oxide formed above 550℃, both played a main part in the sintering process of cinder. In the range from the temperature at which the sintering began to about 400℃ and in temperatures above 550℃, the resistance increased with the rise of temperature, whereas in the range from 400 to 550℃ it decreased with the rise of temperature by the progress of the reaction of oxide formation due to "the first decreasing change in weight". It was also found that an addition of over 30 per cent of pyrite to pyrrhotite would enable to complete the roasting almost without the sintering of cinder

Formation of Lamellar and Spheroidal Graphite in Cast Iron in Relation to the Micro-Segregation of Silicon

By the addition of ferrosilicon to molten cast iron, not only is there the inoculating effect but also under certain conditions spheroidal graphite can be formed. In order to investigate the role of silicon as an additive, experiment was carried out using the potentiostatic technique as a means of etching the primary structure. When the melt was treated with large amounts of refined ferrosilicon, microregions in which silicon was highly concentrated were observed in the cast state and spheroidal graphites were mostly formed in such regions. This suggests that the formation of spheroidal graphite is related to the local super-saturation of carbon caused by adding silicon to the melt