In the smelting process, due to improper dosing or charging and excessive decarbonization and other reasons, sometimes the carbon content in steel or iron does not meet the expected requirements, then it is necessary to carburize the steel or liquid iron. The main substances commonly used for carburizing are anthracite powder, carburized pig iron, electrode powder, petroleum coke powder, asphalt coke, charcoal powder and coke powder. The requirements for the carburizer are that the higher the fixed carbon content, the better, and the lower the content of harmful impurities such as ash, volatile matter and sulfur, the better, so as not to pollute the steel.
The smelting of castings uses high-quality recarburizer after high temperature roasting of petroleum coke with few impurities, which is the most important link in the carburizing process. The quality of the recarburizer determines the quality of the liquid iron, and also determines whether the graphitization effect can be obtained. In short, reducing iron shrinkage recarburizer plays an important role.
When all scrap steel is melted in electric furnace, the recarburizer that has been graphitized is preferred, and the recarburizer that has been graphitized at high temperature can change the carbon atoms from the original disordered arrangement to sheet arrangement, and sheet graphite can become the best core of graphite nucleation to promote graphitization. Therefore, we should choose a recarburizer that has been treated with high temperature graphitization. Because of the high temperature graphitization treatment, the sulfur content is generated SO2 gas escape and reduce. Therefore, the sulfur content of high-quality recarburizer is very low, generally less than 0.05%, and the better is even less than 0.03%. At the same time, this is also an indirect indicator of whether it has been treated with high temperature graphitization and whether graphitization is good. If the selected recarburizer is not graphitized at high temperature, the nucleation ability of graphite is greatly reduced, and the graphitization ability is weakened, even if the same amount of carbon can be achieved, but the results are completely different.
The so-called recarburizer is to effectively increase the carbon content in the liquid iron after adding, so the fixed carbon content of the recarburizer must not be too low, otherwise to achieve a certain carbon content, you need to add more products than the high-carbon recarburizer, which undoubtedly increases the amount of other unfavorable elements in the carburizer, so that the liquid iron can not get better returns.
Low sulfur, nitrogen and hydrogen elements are the key to prevent the production of nitrogen pores in castings, so the nitrogen content of the recarburizer is required to be as low as possible.
Other indicators of the recarburizer, such as the amount of moisture, ash, volatiles, the lower the amount of fixed carbon, the higher the amount of fixed carbon, so the high amount of fixed carbon, the content of these harmful components must not be high.
For different melting methods, furnace types and the size of the melting furnace, it is also important to choose the right recarburizer particle size, which can effectively improve the absorption rate and absorption rate of the recarburizer in the liquid iron, and avoid the oxidation and burning loss of the carburizer caused by too small particle size. Its particle size is best: 100kg furnace is less than 10mm,500kg furnace is less than 15mm,1.5 ton furnace is less than 20mm,20 ton furnace is less than 30mm. In converter smelting, when high carbon steel is used, recarburizer containing few impurities is used. The requirements for the recarburizer used in the top blown converter steelmaking are high fixed carbon, low content of ash, volatile and sulfur, phosphorus, nitrogen and other impurities, and dry, clean, moderate particle size. Its fixed carbon C≥96%, volatile content ≤1.0%, S≤0.5%, moisture ≤0.5%, particle size in 1-5mm. If the particle size is too fine, it is easy to burn, and if it is too coarse, it floats on the surface of the liquid steel and is not easy to be absorbed by the molten steel. For the induction furnace particle size in 0.2-6mm, of which steel and other black metal particle size in 1.4-9.5mm, high carbon steel requires low nitrogen, particle size in 0.5-5mm and so on. The specific need according to the specific furnace type smelting workpiece type and other details specific judgment and selection.
Post time: Aug-25-2023