Graphitized petroleum coke recarburizer is a highly efficient recarburizer commonly used in steel smelting or the foundry industry. It has the characteristics of high carbon content (usually ≥98%), low sulfur (≤0.05%), and good adsorption through high-temperature graphitization treatment. The following are the specific principles, application steps, and precautions of its recarburization:
1. How does graphite recarburizer increase carbon?
During the smelting process (such as electric furnace, medium frequency furnace), when the carbon content of molten steel or molten iron is lower than the target value, graphitized petroleum coke releases carbon atoms through high-temperature dissolution, diffuses into the metal liquid, and increases the carbon content. At the same time, the carbon structure of graphitized petroleum coke is stable, similar to graphite flakes, with fast dissolution speed and high absorption rate, usually up to 90%, 95%, and few impurities, avoiding negative impact on metal properties.
Graphitized petroleum coke is usually carburized by the following steps: First, pre-treatment is performed to crush the graphitized petroleum coke, and the block graphitized petroleum coke is crushed to a particle size of 1-5mm to ensure rapid dissolution. If it is damp, it needs to be dried at 200℃-300℃ to avoid splashing caused by moisture. It can be added in the middle of smelting after the charge is partially melted, and melted to about 60% or 70% inside the furnace, and high temperature is used to accelerate diffusion. If the carbon content is insufficient, it can be added with the flow during steel tapping or sprayed into the ladle. At the same time, it can be added in layers, and laid in layers with scrap steel, pig iron, and other charges to increase the contact area. At the same time, a large amount of one-time addition should be avoided to cause agglomeration, and it should be added in 2-3 installments, with an interval of 5-10 minutes each time.
The optimal temperature range for smelting is 1450-1550℃ (molten iron) or 1600-1650℃ (molten steel). If the low temperature is <1400℃, the carburizer will float and the absorption rate will decrease; if the temperature is too high,>1650℃, the carbon burnout may be aggravated. Electromagnetic stirring, argon injection, or mechanical stirring can also be used to accelerate carbon diffusion, shortening the carbonization time, which usually takes 10-20 minutes. After the smelting is completed, take a sample of the molten metal and use a spectrometer or carbon-sulfur analyzer to detect the carbon content to ensure that the target value is reached, such as 3.2-3.8% for cast iron.
2. What specifications of graphitized petroleum coke have the best carbonization effect?
The optimal range of carbon content is≥98.5%. The higher the carbon content, the greater the effective carbon contribution of a unit of carbonizer, which can reduce the amount added and reduce the risk of impurities introduced. For example, a carbonizer with a carbon content of 99% uses about 4kg less per ton of molten iron than a carbonizer with a carbon content of 95%, and has fewer impurities such as sulfur and nitrogen.
The optimal range of sulfur content is ≤0.03%. Sulfur is a harmful element in cast iron and steel. For example, ductile iron requires S≤0.02%. Low-sulfur carbonizers can avoid the cost of additional desulfurization due to excessive sulfur after smelting. If the sulfur content is reduced from 0.05% to 0.02%, the sulfur load per ton of molten iron is reduced by 0.3kg, significantly reducing the risk of casting brittleness.
The best range of particle size: If it is an electric furnace/intermediate frequency furnace, it is suitable for 3-10mm, which dissolves quickly at high temperature and has less floating loss. Small induction furnace/ladle carbon increase: 1-5mm, which can accelerate diffusion and is suitable for rapid smelting. If it is too coarse>10mm, it dissolves slowly and is easy to sink to the bottom; if it is too fine<1mm, it is easy to oxidize, burn, or float, and the absorption rate drops by more than 20%.
The best indicator of graphitization degree: resistivity ≤0.8μΩ·m or XRD detection of graphite crystal structure is complete. The higher the degree of graphitization (carbon atoms are arranged in layers), the more uniform the carbon release, and the dissolution rate is 30%-50% faster than that of ungraphitized petroleum coke. The sharpness of the (002) crystal face peak can be observed by X-ray diffraction (XRD), or the resistivity can be measured (the higher the degree of graphitization, the lower the resistivity).
Other impurity control: Ash (Ash%): ≤0.5%, high ash content will form slag phase and hinder carbon diffusion. Volatile matter (VM%): ≤0.5%, high volatile matter is easy to produce gas, resulting in pore defects in molten metal. Moisture (Moisture%): ≤0.3%, moisture exceeding 0.5% may cause smelting splashing.
Through the above methods, graphitized petroleum coke can efficiently and stably achieve molten metal carbonization while reducing the introduction of impurities, and is the preferred material for the casting and metallurgical industries.
