Control De Oxigeno En FP

Control de Oxigeno en FP

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Jorge Enrique Mantilla Barba
     
Acudo a Uds. con el objetivo de consultar información sobre:
 
         La importancia de controlar los ppm de oxigeno en Horno eléctrico, tienen un estándar (valores) para salida de FEA?
         Tienen estándar de llegada a FP?
         Como se logra un control más efectivo de estas ppm en FP?         Cuál es la forma más rápida de reducirlas en FP?
 
en este momento nuestro % de rendimiento de FeSi es muy bajo, el tratamiento de la escoria se ha convertido en un proceso critico  y tenemos muchas perdidas en tiempo en el FP.
muchas gracias
 
17 de maio, 2011
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Raimundo Augusto F O Fortes
     Dear Barba,
 
Roughly speaking, the soluble oxygen content (ppm O) can be managed according to:
- the steel grade requirements (quality)
- EAF productivity requirements vs. metallic yield

Steel grade requirements:
 
Soluble oxygen content is important for C, S and P removal.  
 
- Low sulfur grades require low oxygen content arriving at Ladle Furnace (LF). As the sulfur removal in EAF is almostnegligible, the soluble oxygen should be lower than 500 ppm. Besides, excessive slag carryover from EAF will also affect the soluble oxygen in LF. Hints (final %S and soluble oxygen at end of LF processing):
%S < 0.010%; 10-15 ppm O
%S > 0.020%; 20-35 ppm O
 
Of course, if there is no LF station, the soluble oxygen shall be < 500 ppm O.
Remark: be careful with deep oxygen removal (< 10 ppm O),because side effects like nozzles clogging at caster may come true.
  
- Low phosphorous grades (%P < 0.010%), higher oxygen potential 800-1000 ppm O is required, leading to higher Fe losses through FeO in the slag. However, slag off followed by intense carbon injection before tapping can provide significant decrease of soluble oxygen (< 600 ppm), but be careful with phosphorous reversion.  
 
- Lowcarbon grades (%C < 0.06%) follows the low phosphorous job procedures, except for the intense carbon injection, because sometimes recarburization takes place or even the carbon content of Fe-alloys might present a higher pick up. Most of times, the soluble oxygen content reaches 900-1100 ppm before tapping.
 
- Medium and high carbon grades (%C > 0.10%) are not supposed to be over oxidized forcarbon removal. Therefore, the soluble oxygen can be achieved around 400-500 ppm, saving Fe from oxidation.
 
- Low total oxygen content (clean steel), in these grades, high soluble oxygen content on tapping is definitely undesired, mainly if the required carbon is low and other deoxidant agent shall be used instead (Si or Al-killed steels), producing too much oxides (inclusions). If such inclusionsare not removed or modified on time, you are in trouble. In these cases "Total" oxygen is higher and more important than the soluble oxygen content.
 
EAF productivity
 
- If the steel market is demanded, you are pushed to cast more billets. Hence, chemical energy is required in EAF, and aggressive oxygen injection and gas takes place. In this scenario, the soluble oxygen is usually 700 - 800 ppmand FeO > 30%.
 
- Try to get FeO+MnO < 2% in the LF slag. There are several slag agents like CaC2 and SiC that helps on FeO+MnO reduction
 
- If you are not producing specialty steels, try to be away from Al in the LF. A minor additon on EAF tapping can used (0.1 kg Al/ton) for primary deoxidaton. But be aware that if EAF process at your mill is not enogh stable, sometimes very low soluble oxygencan be achieved and nozzle clogging may occur.
 
- If FeSi yield is low, check the amount of slag carry over from EAF through the ladle. That should be your first step. Check the taphole diameter (if it is EBT type) and quick tilting back.  
 
Regards,
RFortes

From: Jorge Enrique Mantilla Barba
Posted: Tuesday, May 17, 2011 6:02 PM
Subject: Control de Oxigeno en FP
Acudo a Uds. con el objetivo...