how to choose recarburizer for casting
The recarburizer is a follow-up product of black or gray particles of coke with high carbon content. It is added to the metal smelting furnace to increase the carbon content in the molten iron, and on the one hand, it can reduce the oxygen in the molten iron,on the other hand, it is more important to improve the mechanical properties of smelted metals or castings.
here are many sources of recarburizers with different forms, and their prices vary greatly according to their processing technology and composition. The traditional smelting method is similar to cupola smelting: pig iron, reheating charge, scrap steel, ferroalloys, etc. are used as metal charge; The new synthetic cast iron production process: scrap steel is used as charge, and recarburizers are used to adjust the carbon equivalent of molten iron. The latter production method is easier to ensure high-quality molten iron, and at the same time greatly reduces costs by using less or replacing pig iron with scrap steel. In layman's terms, using recarburizers, we can use the worst scrap steel to make the best castings.
Selection of recarburizer and its index performance.
In the smelting process, due to improper ingredients or charging and excessive decarburization and other reasons, sometimes the carbon content in steel or iron does not meet the expected requirements,at this time, it is necessary to add carbon to the steel or molten iron. The main substances usually used to increase carbon are anthracite powder, carbonized pig iron, electrode powder, petroleum coke powder, pitch coke, charcoal powder and coke powder. The requirement for recarburizer is that the better with the higher the fixed carbon content and the lower the content of harmful impurities such as ash, volatile matter and sulfur,so as not to pollute the steel.
The smelting of castings uses high-quality recarburizers from petroleum coke with few impurities after high-temperature sintering, which is the most important link in the recarburization process. The quality of the recarburizer determines the quality of the molten iron, and also determines whether a good graphitization effect can be obtained. In short, the recarburizer plays an important role in reducing the shrinkage of molten iron.
When smelting all scrap steel in an electric furnace, it is preferred to use graphitized recarburizers. After high temperature graphitization recarburizers, the carbon atoms can change from the original disorderly arrangement to the flake arrangement, and the flake graphite can become graphite. The best core of the nucleus to facilitate graphitization. Therefore, we should choose recarburizers that have undergone high-temperature graphitization. During the high-temperature graphitization process, the sulfur content is reduced by the escape of the generated SO2 gas. Therefore, high-quality recarburizers have very low sulfur content, generally less than 0.05%, and even better, less than 0.03%.If the selected recarburizer is not subjected to high temperature graphitization treatment, the nucleation ability of graphite will be greatly reduced, and the graphitization ability will be weakened,even if the same carbon content can be achieved, the results are completely different.
The so-called recarburizer is to effectively increase the carbon content in the molten iron after being added, so the fixed carbon content of the recarburizer must not be too low, otherwise, to reach a certain carbon content, you need to add a higher carbon content There are more samples of the recarburizer, which undoubtedly increases the amount of other unfavorable elements in the recarburizer, making the molten iron unable to obtain better returns.
Low sulfur, nitrogen, and hydrogen are the key to preventing nitrogen pores in castings, so the lower the nitrogen content of the recarburizer, the better,to other indicators of the recarburizer, such as the lower the amount of moisture, ash, and volatile, the higher the fixed carbon content, so the high fixed carbon content, the content of these harmful components will not be high.
For different smelting methods, furnace types and sizes of smelting furnaces, it is also important to select the appropriate recarburizer particle size, which can effectively improve the absorption speed and absorption rate of the recarburizer by the molten iron, and avoid oxidation and burnout of recarburizer caused by too small particle size. The particle size of the recarburizer is preferably less than 10mm for a 100kg furnace, less than 15mm for a 500kg furnace, less than 20mm for a 1.5-ton furnace, and less than 30mm for a 20-ton furnace.
When smelting high-carbon steel grades in a converter, a recarburizer with few impurities is used. The requirement for the recarburizer for top-blown converter steelmaking is to have high fixed carbon, low ash, volatile content, sulfur, phosphorus, nitrogen and other impurities, dry, clean, and moderate particle size，its fixed carbon C≥96%, volatile matter≤1.0%, S≤0.5%, moisture content≤0.5%, particle size is 1-5mm. If the particle size is too fine, it is easy to burn, and if it is too coarse, it will float on the surface of molten steel and will not be easily absorbed by molten steel.The particle size of induction furnace is 0.2-6mm, of which steel and other ferrous metals are 1.4-9.5mm, high-carbon steel requires low nitrogen, and the particle size is 0.5-5mm, etc. Specific requirements for smelting workpieces according to specific furnace types specific judgment and selection of the details and so on.
Anyang Huatuo Metallurgy can supply various types of recarburizer such as calcined petroleum coke, graphitized petroleum coke, graphite carbon etc, welcome for consult.