Macro Inclusions during Continuous Casting

[WLR]

I would like o find out more about the following:

Macro calcium aluminate inclusions found in medium carbon Al-killed steel after casting on a six strand bloom caster.

Inclusions found on these steel qualities reveal high levels of alumina (58-64%), reasonable lime contents (15-22%), low silica and MgO and traces of sodium, MnO and Ti2O.
It is clear that casting powder is involved due to the sodium present (± 1.8%), but is does not explain the high alumina content.

What could be possible sources ? Could these inclusions originate in the ladles or from casting refractories such as submerged entry nozzles or refractory material used in the slide gates? All casting refractories used are Al-C. Tap blocks used in ladles around tap hole are TAB alumina (almost pure alumina). My opinion is that these are not inclusions that form within the tundish or mould since many of the inclusions can be traced back to a second heat in a sequence casting whereas the first heat was clean. Thus I speculate that these inclusion might have been present during steelmaking and ended up in the mould, floated out to the steel / slag interface and got entrained due to some turbulence on the mould meniscus level.

Any info would be of great help.
Thanks

 

[EdStainless]

I have seen inclusions that were carried over from earlier operations (melt or refine) and then agglomerated with mold powder.
What about your filtering practices?
I presume that the ladles are bottom pour. It sound like you have some level control issues if you are experiencing turbulance in the tundish or mold.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[TVP]

I agree with your evaluation WLR. The calcium aluminate inclusions sound like normal remnants of the deoxidation process. These inclusions are often found with mold powder because they "knock off" the mold powder as they pass through the mold during casting.