The Quality Of Recarburizer
Jan 20, 2025
The quality of recarburizer can be measured by multiple indicators. The following are some of the main criteria:
1. Fixed carbon content
Definition: Fixed carbon is the truly useful part of the recarburizer. The higher its value, the better the recarburization effect. The fixed carbon content is obtained by calculating the moisture, volatile matter, ash and sulfur content in the sample.
Standard: Generally speaking, the fixed carbon content of high-quality recarburizer should be greater than 96%.
2. Ash content
Definition: Ash is the residue left after the recarburizer is burned at high temperature. The lower its content, the better.
Effect: Recarburizers with high ash content are prone to produce a lot of smoke and slag during the smelting process, increase energy consumption, reduce carbon absorption rate, and prolong operation time, increase power consumption and labor.
Standard: The ash content of graphite recarburizer is low, about 0.5% to 1.0%; while the ash content of calcined anthracite is high, even if it is high-quality, it will not be lower than 4% to 5%.
3. Sulfur content
Effect: Sulfur is a harmful element that interferes with spheroidization. For the raw iron liquid for producing ductile iron, the sulfur content should be strictly controlled. For gray cast iron, an appropriate amount of sulfur can stabilize pearlite, but excessive sulfur is harmful.
Standard: The sulfur content of the carburizer for ductile iron should be as low as possible, generally requiring S≤0.015%; while the sulfur content of the carburizer for gray cast iron can be slightly higher, but it should also be determined according to specific needs.
4. Volatile matter
Definition: Volatile matter is the gas and water that escapes from the carburizer during heating. The lower its content, the better.
Effect: Volatile matter entering the molten steel will increase the gas content in the molten iron and increase the risk of pore defects in the casting.
Standard: The volatile matter of a properly treated carburizer should be below 0.5%.
5. Particle size
Effect: The particle size of the carburizer should be selected according to different smelting methods, furnace types and the size of the smelting furnace. Recarburizers with uniform and moderate particle size can improve the carbon absorption rate.
Standard: For example, the particle size for induction furnaces is between 0.2 and 6 mm; the particle size of steel and other ferrous metals is between 1.4 and 9.5 mm; high carbon steel requires low nitrogen and a particle size between 0.5 and 5 mm.
6, moisture
Effect: The water brought into the molten steel will increase the hydrogen content in the molten steel, which will have an adverse effect on the quality of the castings.
Standard: The total moisture index of the recarburizer should be as low as possible, the moisture content of the small bag recarburizer should be ≤1%, and the moisture content of the raw coke before crushing and packaging should be ≤3%.
7, nitrogen content
Effect: The role of nitrogen content in gray cast iron is two-sided. The right amount of nitrogen can stabilize pearlite, bend flake graphite, and passivate the tip, thereby improving the mechanical properties of gray cast iron; but excessive nitrogen will cause crack-like nitrogen pore defects in castings.
Standard: Gray cast iron mostly uses coal or petroleum coke recarburizers, and the nitrogen content of about 1000ppm can meet the requirements of most casting materials. For the production of ductile iron, it is necessary to choose graphite recarburizers or graphitized recarburizers with lower nitrogen content.
In summary, the difference between the quality of recarburizers requires comprehensive consideration of multiple indicators such as fixed carbon content, ash content, sulfur content, volatile matter, particle size, moisture content and nitrogen content. In practical applications, the appropriate recarburizer should be selected according to specific needs and furnace conditions.
