As the name suggests, the recarburizer increases the molten iron's carbon content. The steelmaking recarburizer is used for casting, cast iron, and cast steel.
The commonly used charge in smelting is pig iron, scrap steel, and return charge. The carbon content of pig iron is high, but the purchase price is higher than that of scrap steel.
Therefore, increasing the amount of scrap steel, reducing the amount of pig iron, and adding carbonizers can play a certain role in reducing the cost of castings.
Commonly used recarburizers include carbonized pig iron, electrode powder, petroleum coke powder, charcoal powder, and coke powder.
In the smelting process, due to improper batching or charging and excessive decarburization, sometimes the carbon content in the steel does not meet the requirements of the peak period, and carbon should be added to the molten steel at this time.
In converter smelting of medium and high carbon steel, petroleum coke with few impurities is used as a recarburizer. The requirements for recarburizers for top-blown converter steelmaking are that the fixed carbon should be high, and the ash, volatile, sulfur, phosphorus, nitrogen, and other impurities should be low, dry, clean, and moderate in particle size.
When the recarburizer is used in the intermediate frequency electric furnace smelting, it can be added to the middle and lower parts of the electric furnace according to the ratio or carbon equivalent requirements. The recovery rate can reach more than 95%.
If the carbon content is insufficient to adjust, first clean the slag in the furnace, then add a recarburizer, heat the molten iron, electromagnetic stirring, or manual stirring to dissolve and absorb the carbon, and then the recovery rate can be about 90%.
If the low-temperature carburizing process is adopted, that is, only part of the charge is melted, and the molten iron temperature is low, all the carburizers are added to the molten iron at one time, and at the same time, the solid charge is pressed into the molten iron to prevent it from being exposed. molten iron surface. In this method, the carburization of molten iron can reach more than 1.0%. Therefore, the use of recarburizers in induction furnace smelting is also different according to the process requirements.
Casting recarburizer must pay attention to the following aspects in use, otherwise, it will affect its absorption rate.
Influence of particle size of recarburizer: The carburization process using recarburizer includes dissolution diffusion process and oxidation loss process. The particle size of the recarburizer is different, so the dissolution diffusion rate and oxidation loss rate are also different.
Influence of the amount of recarburizer added: Under the conditions of a certain temperature and the same chemical composition, the saturated concentration of carbon in the molten iron is certain.
Under a certain degree of saturation, the more recarburizer added, the longer the time required for dissolution and diffusion, the greater the corresponding loss, and the lower the absorption rate.
The effect of temperature on the recarburizer absorption rate: Above the equilibrium temperature, the recarburizer absorption rate decreases. When the carbonization temperature is below the equilibrium temperature, it is due to the lower temperature.
The saturated solubility of carbon decreases, and at the same time, the dissolution and diffusion rate of carbon decreases, so the yield is also lower; when the carbon increase temperature is at the equilibrium temperature, the absorption rate of the carburizer is the highest.
The influence of molten iron stirring on the absorption rate of the recarburizer: the appropriate stirring time of the molten iron should be suitable to ensure that the recarburizer is completely dissolved.
These are the most important factors that usually affect the use effect and absorption rate of recarburizers.
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