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During steelmaking, carbon is the core element that determines the performance of steel (such as low-carbon steel has good toughness and high-carbon steel has high hardness), but oxidation reactions (such as pre-treatment of molten iron and oxygen blowing in converter) will cause the carbon content to decrease, and it needs to be supplemented by carbon enhancers.
The performance of carbon enhancers is closely related to their types (such as graphite, petroleum coke, coal quality, etc.).
The overall advantages and disadvantages are as follows:
Advantages
Accurately regulate carbon content: it can be flexibly adjusted according to steel grade requirements (such as low carbon steel 0.02%-0.25% and high carbon steel 0.6%-2.0%) to ensure the stability of the molten steel composition and ensure subsequent rolling, forging and other processing performance.
Improve smelting efficiency: Carbon oxidizes and exotherms at high temperatures (C+O₂=CO₂↑+ heat), especially in arc furnaces, the addition of carbon enhancers can accelerate the melting of scrap steel, shorten the smelting time, and reduce energy consumption (such as electricity consumption).
Reduce production costs: Compared with the use of high-carbon pig iron (high carbon content but more impurities), high-quality carbon enhancers (such as graphite, low-sulfur petroleum coke) have a higher fixed carbon content (usually > 90%) and fewer impurities, which can not only meet the carbon increase needs, but also reduce the cost of subsequent handy removal processes.
Improve the purity of steel: High-purity carbon enhancers (such as natural graphite) have low ash, sulfur, phosphorus and other impurities (sulfur <0.05%), which can reduce inclusions (such as silicates) and harmful gases (such as H₂, N₂) in the steel and improve the toughness and fatigue properties of the steel.
Disadvantages
Impurities can easily affect the steel quality: inferior carbon enhancers (such as coal-based carbon enhancers) contain high sulfur, phosphorus and ash (sulfur may be > 0.5%), which will cause harmful elements in the steel to exceed the standard and reduce the weldability and corrosion resistance of the steel (such as sulfur, which will cause heat brittleness).
Unstable absorption efficiency: The absorption effect of the carbon enhancer is affected by particle size (it is easy to sink to the bottom if it is too coarse and easy to be oxidized and burned by too fine), addition time (it is easy to be burned during the oxidation period, and needs to be added during the reduction period), liquid steel temperature, etc. If improper control will cause fluctuations in the carbon content, it needs to be adjusted twice to increase the process complexity.
High process requirements: It is necessary to strictly match the type of carbon enhancer and steel (for example, high-quality steel requires low-sulfur graphite, and ordinary steel can use petroleum coke), and the addition amount needs to be accurately controlled (excessive amount will cause carbon exceeding the standard, decarbonizing treatment, increasing costs), and high operating accuracy requirements.
Type limitations: Different carbon enhancers have inherent defects, such as petroleum coke carbon enhancers may have high nitrogen content (causing the nitrogen exceeding the standard in steel and causing aging embrittlement); coal-quality carbon enhancers have low fixed carbon (usually <85%) and poor carbon increase efficiency, which is only applicable to low-demand steel grades.
