These specific carbon raiser cost results from the cost price of the recarburiser and the achieved carbon yield. In induction furnaces, the carbon recovery is closely associated with following parameters:
1. Method and sequence of charging
- First add successively scrap steel + recarburiser (RC)
- Operation with a heel: First of all the heel is to be diluted through adding scrap steel, followed by recarburiser
- First addition of recarburiser at approx. 800°C and then in steps of approx. 100°C
- After charging of steel scrap, add returns, pig iron and other alloys.
- After the complete dissolution of the recarburiser, add FeSi-75
- %CE=%C+1/3% SI (S and P elevate % CE as well)
- With GJL, sulphur is to be added at the end of the melting time; sulphur has a strong inhibitory effect on the solubility of carbon.
2. Cleanliness of charge materials
- Minimise slagging: Rusty scrap and non-shot-blasted returns increase the slag, when deslagging the carbon which is trapped in the slag is lost.
3. Charge make-up
- I. % heel (yes/no)
- II. % steel (>40% improves carbon recovery opens more options to use various recarburisers)
- III. % returns
- IV. % pig iron
4. Furnace type and 5. Stirring action of furnace
- Through the good stirring action of line frequency crucible melting furnaces, a good dissolution of the recarburiser is achieved.
- With medium frequency crucible furnaces and moderate stirring actions the carbon dissolation is acceptable.
- Distance between the top of the induction coil and the maximum furnace filling level – poor stirring action and difficult dissolution at a distance of >250mm
6. Power of furnace
- >0,5 MW/t: Through the high power-/meling rate the recarburiser has less time to dissolve.
- With high-power furnaces the recarburiser has only 15 – 20 minutes time to dissolve between the first liquid phase and the extraction of the first sample.
7. Other accompanying elements
- The content of other metal-based alloys (Si, Cu, Mn, etc.) should be kept as low as possible while adding the recarburiser.
- S-contents >0,04% severely impede the solubility of carbon, i.e. grey iron returns as well as sulphur containing alloys should be added after the steel scrap has absorbed the recarburiser.
9. Size and morphology of the recarburiser
- The grain size should not exceed 5mm. It should have a high surface-to-volume ratio.
- “Better a bit to fine than too coarse“
- Ideal is 0,1–3,00mm and a dust friction content <0,1mm should be avoided.
10. Target carbon content
- Carbon saturation of the iron reduces the solubility of further carbon.