There are lots of cases that carbon pick up is seen between ladle and tundish in our plant during continuous casting of slab steel (even more than 0.02 wt%). What is the reason of this phenomenon?
We use rice powder, mgo mass gunning and dry mass in the tundish and alumina graphite ladle nozzle and stopper.
Best regards
Are you using C-Magnesia brick in your ladle? If yes, Carbon might be coming from refractory. Graphite is also a source of carbon. Your FeO in slag should be very low if carbon pickup is observed.
Dear Mr Srivastava
Yes. We use magnesia carbon brick in ladle. But in many cases we don't have any carbon pick up during ladle furnace treatment while carbon pick up is seen just between final sample of ladle furnace and tundish sample.
What is there in your tundish flux? Are you using rice husk? Because ReOxidation I have heard about but carbon pickup in tundish is new to me.
Yes. We use rice husk in the tundish which contain carbon (approximately 40% wt carbon), It can be one of the carbon pickup in molten steel. But we don't have carbon pickup always while use rice husk in all heat. What do you think about sampling method? May be when molten steel sampling is done at surface of steel, carbon of rice husk enter to sample and cause carbon pickup in sample.
Yes, it is possible that your samples become contaminated with rice husk. For which you can take multiple samples from the tundish at different depths. If readings at all depth are same then it may not be due to rice husk. Also take the sample at both areas 1. Near turbostop 2. Farther the turbostop
Yes. Sampling is so important. In fact we have two different phenomenon:
1. Carbon pick up in tundish sample which disappears in slab sample: in that case wrong tundish sampling can be the reason.
2. Carbon pick up in tundish sample which remains in slab sample: reason of this phenomenon is not clear.
what is your opinion about this two phenomenon?
And to 1. This is not wrong sampling. This is all about the location where from you take the tundish sample. If you are taking sample from the place where turbulent mixing is very high, you may get carbon in your sample because now lot of molten rice husk has been mixed with steel. People use weir for this purpose so that interfacial mixing of slag with steel can be reduced. You change the location of sampling means go deeper into the steel you might find lower carbon.
Ans-2 if carbon pickup is not observed in slab sample then I believe there is no problem because slab is the main product to go for rolling.
Dear Amiy
Please see the attached picture which shows a carbon pick up between ladle and tundish. Carbon pick up is not disappears in slab sample.
Please calculate the amount of carbon picked up per heat in kg using following method.
(%Carbon in slab- %carbon in tundish )* heat size
Also take more samples from slab and plates both. Don't cut the sample from centre plane because macrosegregation may increase the carbon. Provide plate samples also.
Dear Amiy
In fact, carbon pick up between ladle and tundish is the main problem, not between tundish and slab. We dont have any carbon pick up between tundish and slab samples at all.
As we can see at attached picture above, in low carbon steel that no graphite added to ladle, there is a significant carbon pick up between ladle and tundish sample, while carbon content in ladle during ladle furnace operation is approximately fix.
The problem of this kind of carbon pick up is that carbon does not decrease such in slab tundish.So I am looking for some reason of this phenomenon?
Dear Sharifian,
I am not sure about heat size in plant but if we consider 100 ton liquid steel, it makes for about 25-30 kg carbon pick-up in each heat. This amount of carbon seems too much for ladle refractory, mold powder, stopper rod, ladle shroud or nozzle.
Is this case common in all heats in tundish sequence or it happens randomly? As far as I saw in picture, FeSi, FeMn, FeCr additions are not the case. But have you changed the additives in storage bins recently, the flux additions bins might be contaminated by previous materials.
Dear Alan
This case happens randomly.
Also we are talking about carbon pick up in tundish, which no ferro alloys are added to tundish. So I think ferro alloys can not cause carbon pick up in tundish.
This problem is not new and we have had it for several years.
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