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Petroleum coke test and production practice can well prove that graphite carburizer can promote nucleation by increasing the number of nucleation points in molten iron in the presence of heterogeneous core. In order to improve the nucleation ability of the carburizer, it is necessary to understand some additional crystal structure. Only the graphite structure of the carburizer can better improve the properties and ability of the molten iron. The carbonization agent instead of the real name structure can not enhance the nucleation ability of the molten iron. Based on this idea, even if all melting parameters remain unchanged, graphite-structured carburizers are used to replace non-graphite-structured carburizers, or vice versa, it is possible to change the properties and abilities of the molten iron, and the change in the nucleation ability of the molten iron (inadequate or excessive nucleation) changes the solidification process, thereby altering the casting process. Microstructure of iron.
Many technicians have done a lot of experiments on the inoculation effect of carburizers. After a lot of tests, the white depth of gray cast iron obtained by different carburizers, from non-graphite structure materials, such as calcined petroleum coke to various graphite structure carbon, comes to the conclusion that the crystallinity of the carburizer material will affect the gray cast iron. The reduction of white depth. In the case of proper use, the better the material, the better the effect of carburant on reducing the whitening depth (graphitized carburant, petroleum coke carburant). Therefore, it is very important for many manufacturers to choose their own suitable carburizing agents when choosing materials. Looking at all kinds of research on carburizers at home and abroad, it can be found that most of the current research reports focus on the study of carburizing process, only based on the existing several carburizers to carry out carburizing process tests, but for the choice of carburizing materials, preparation, carburizing agent in molten steel dissolution and diffusion state. There is little research on the factors affecting the carburizing effect of the carburizer, and the research on the characteristics of the carburizer itself is not deep enough. Moreover, the current process experiments are relatively opposite, lack of contrast, and do not combine the advantages of various process methods together. The improvement measures for the shortcomings of the existing process are still not comprehensive.
At present, the main carburizers in the market are graphite carburizer, graphitizing carburizer, calcined petroleum coke carburizer, coal-based carburizing petroleum coke, graphite electrode carburizer and so on. According to the cost, of course, the higher the material, the more expensive the carburizer, but now the use of manufacturers will be based on the principle of low price and high taste. Purchasing, therefore, requires manufacturers to further study and analyze the characteristics of various carburizers, further improve the performance of the use of carburizers, with low-cost production process to produce more high-quality carburizer products more in line with the needs of mass manufacturers. First become the crystalline core of graphite, as everyone knows, carbon and silicon have a very strong inoculation effect, so they are very helpful to electric furnace and low carbon ferrosilicon smelting. The amount of silicon carbide is generally in the range of 0 5%. In the past two years, silicon carbide has been used more in foundry production, according to the use of the situation, the effect is better, especially in smelting, increase the graphite core, increase the number of nodular graphite iron, improve the graphite morphology of gray iron are very useful. Petroleum coke silicon carbide is widely used in foreign countries. It is added to both electric furnace and cupola. Because the melting point of silicon carbide is very high, about 2700 degrees, it is impossible for us to have such a high temperature in the ordinary foundry furnace of petroleum coke, so Zhou Jiyang used the word "melting" when he talked about the decomposition of silicon carbide in his paper, that is, at our casting melting temperature, the dissolution of silicon carbide. When the melting state gradually decomposed, diffusion, relatively slow, so the time to add silicon carbide in the furnace should be earlier than other alloys, generally in the furnace charge melting to one third to half of the time added, so that it has sufficient temperature, time conditions to decompose. 1. effect of carburizing particle size
The carburizing process using carburizing agent includes dissolution and diffusion process and oxidation loss process. The size of the carburizing agent is different, and the rate of dissolution and diffusion and the rate of oxidation loss are different. The absorption rate of the carburizer depends on the comprehensive effect of the dissolution and diffusion rate of the carburizer and the oxidation loss rate: in general, the carburizer particles are small, the dissolution rate is fast, and the loss rate is large; the carburizer particles are large, the dissolution rate is slow, and the loss rate is small. The size of the carburizing agent is related to the diameter and capacity of the furnace. In general, the diameter and capacity of the furnace is large, the particle size of the carburizer is larger; conversely, the particle size of the carburizer is smaller. The granularity of crystalline graphite is required to be 0.5-2.5 mm for electric furnace melting below 1 t, 2.5-5 mm for crystalline graphite for 1t-3 t, 5.0-20 mm for crystalline graphite for 3t-10 T and 0.5-1 mm for crystalline graphite for coating in ladle.
2. the influence of adding amount of carburizing agent.
Under certain conditions of temperature and chemical composition, the saturation concentration of carbon in molten iron is certain. The dissolution limit of carbon in cast iron is ([C%]=1.3+0.0257T-0.31 [Si%]-0.33 [P%]-0.45 [S%]+0.028 [Mn%] (T is molten iron temperature). At a certain saturation, the more the carburizer is added, the longer the dissolution and diffusion time is required, the greater the corresponding loss, and the lower the absorption rate.
3. effect of temperature on the absorption rate of carburant
From the point of view of kinetics and thermodynamics, the oxidation of molten iron is related to the equilibrium temperature of C-Si-O system, that is, O in molten iron reacts with C and Si. However, the equilibrium temperature varies with the target C and Si content. When the molten iron is above the equilibrium temperature, carbon oxidation takes precedence. C and O form CO and C O2. In this way, the oxidation loss of carbon in molten iron increases. Therefore, above the equilibrium temperature, the carburizing agent absorption rate of petroleum coke decreases; when the carburizing temperature is below the equilibrium temperature, due to the lower temperature, the saturated solubility of carbon decreases, and the dissolution and diffusion rate of carbon decreases, so the yield is also lower; when the carburizing temperature is below the equilibrium temperature, the carburizing agent absorption rate is the highest.