Recarburizers are additives used to add carbon to molten iron (primarily cast iron, such as gray iron and ductile iron) during the casting process, particularly during the melting stage.
Their use has a crucial and complex impact on the final quality of castings.
Core Functions and Impacts of Recarburizers
1. Replenishing and Adjusting Carbon Content
Core Function: During the melting process, the carbon content in the molten iron can fall below the desired level due to oxidation, rust, and elemental burnout.
The primary function of a recarburizer is to precisely raise the carbon content of the molten iron to within the required process range.
This is particularly critical when using scrap steel for melting: In modern foundries, large quantities of scrap steel are used as a charge to reduce costs and improve casting performance.
Scrap steel itself has a very low carbon content, so recarburizers are necessary to raise the carbon content from approximately 0.2%-0.8% to the 2.8%-3.8% required for cast iron.
2. Improving molten iron quality
Enhancing graphitization: High-quality recarburizers (especially those that have undergone high-temperature graphitization) can act as "nuclei" for carbon precipitation in the molten iron, promoting graphite nucleation and growth.
This helps produce finer, more evenly distributed type A graphite, thereby improving the mechanical properties of the casting.
Reducing molten iron's tendency to undercool: Good graphitization reduces the molten iron's undercooling, making the crystallization process more stable and reducing the risk of unfavorable microstructures (such as type D graphite).
Purifying molten iron: Adding recarburizers during the smelting process allows them to float on the surface of the molten iron, reducing its contact with air and preventing oxidation.
At the same time, some impurities are removed from the slag along with the recarburizers.
3. Improving the mechanical properties and processability of castings
Improving strength and hardness: By optimizing graphite morphology and matrix structure, the tensile strength, hardness, and elastic modulus of the casting can be increased.
Enhanced Wear Resistance: Evenly distributed graphite has a lubricating effect and can store lubricant, thereby improving the wear resistance of castings.
Improved Machinability: The appropriate graphite morphology (especially flake graphite) acts as a chipbreaker and lubricates the tool during cutting, making castings easier to machine, achieving a smoother surface finish, and extending tool life.
4. Stable Production and Cost Reduction
Stable Composition: The use of recarburizers allows for more precise control of the chemical composition of the final molten iron, reducing quality instability caused by charge fluctuations.
Economical and Efficient: Compared to using only pig iron, the "scrap steel + recarburizer" process can significantly reduce raw material costs.
Summary: Recarburizers are a double-edged sword in casting production:
Positive: They are an indispensable "flavoring agent" and "optimizer" in modern casting processes. They can economically and precisely adjust the composition, significantly improving molten iron quality, ultimately producing high-quality castings with high strength, stable performance, and excellent machinability.
Negative: If inferior recarburizer is used or improperly operated, it will become the source of defects, introduce harmful impurities, and cause a series of serious problems such as porosity, slag inclusions, white cast iron, and graphite floating.
