In the recarburizer field, "carbon content" and "fixed carbon" are two often-confused but distinct indicators. Understanding their difference is crucial for evaluating recarburizer quality and predicting its effectiveness.
"Carbon content" is a theoretical chemical concept that refers to the total mass percentage of all carbon elements in a sample (including carbon in any form). It is measured through elemental analysis.
Fixed carbon: An industrial concept that refers to the mass percentage of solid carbon in a sample that does not volatilize after heating at a specific high temperature and is available for recarburization reactions. It is a calculated value, not a direct measurement.
To use a simple analogy, carbon content is the total weight of a bowl of dry flour, while fixed carbon is like the weight of flour that remains after sieving out water and impurities, which can actually be used to make noodles.
In the steelmaking process, solid carbon that can dissolve in molten iron is required. The fixed carbon indicator directly indicates the amount of this available carbon.
A high fixed carbon content (e.g., FC > 98.5%) indicates that the recarburizer is extremely pure, with very low ash and volatile matter. The absorption rate is high (approaching 95% or even higher) during use, and the recarburization effect is stable and predictable.
Harmful impurities (S, P, N, etc.) and ash introduced into the molten steel are minimal, which helps improve steel quality.
High carbon content but low fixed carbon: This situation indicates that the product contains a large amount of volatile matter.
For example, a sample may have a measured carbon content of 99%, but its calculated fixed carbon value is only 92%. This 7% difference is the volatile matter.
Hazards: When this recarburizer is added to hot molten iron, the 7% volatile matter will quickly vaporize, causing violent boiling and splashing of the molten iron. This not only poses a safety hazard, but also results in extremely low carbon absorption, as most of the carbon escapes as gas, rendering it ineffective in recarburizing. Furthermore, gases in the volatile matter (such as H₂ and N₂) may enter the molten steel, causing defects.
When purchasing and evaluating recarburizers:
- Primarily focus on the fixed carbon metric: The fixed carbon percentage is the gold standard for measuring the active ingredients and purity of the recarburizer. The higher the fixed carbon percentage, the better the quality. Beware of the trap of high "carbon content": Don't be misled by high "carbon content"; always request a complete industrial analysis report.
- Integrate with other indicators: In addition to high fixed carbon, further focus on indicators such as sulfur content (S%) and nitrogen content (N%), which have a significant impact on steel quality.
Fixed carbon is defined as "effective carbon" from an application perspective, while carbon content is simply "total carbon" from a chemical perspective. For recarburizers, "effective" is far more important than "total."
