Steels with low silicon contents ( less than 0.1 %) 5

[stanislasdz]

I want to know more about the steels about low silicon contents les than 0.1 % especially in :

- Steelmaking
- Field of application of these steels

Thanks

 

[TVP]

stan,

I am only familiar with the use of low Si steels for wrought applications (wire/bar/sheet) not for castings. Si is a ferrite strengthener, so reducing the Si content reduces the flow stress, making cold forming/forging easier. These steels are deoxidized with Al, and may also have an addition of V for further grain refining. A synthetic slag is frequently used during ladle refining together with Ar bubbling to float the nonmetallic inclusions so that they can be removed, further improving formability and machinability.

 

[stanislasdz]

great !

Thanks

 

[arunmrao]

Stanislasdz,
You too are branded as a castings guy,like I am. My sympathies. Low Si steels are difficult to manufacture because of ease of oxidation during processing.
They are normally used for stampings,pressings and deep drawn materials.
TVP has explained well the way low Si steel is manufactured.

Is your company diversifying from steel castings into steel products. All your recent postings tend to be leaning that way!

I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
_____________________________________

 

[deadrange]

I'd just like to add my $0.02 worth.

Low Silicon steels, 0.10 wt % or lower are much more difficult to produce to a clean steel practice. Like was previously stated, Al is typically used as the only killing agent. In most cases, since melt shops are catch carbon, the steel is typically blown much lower than needed, thereby increasing the oxygen level. While some Silicon is used, the majority of the killing is done with Aluminum. As we all know Al2O3 is the primary oxide formed, and with the high levels of oxygen alot of oxide is formed. Unlike SiO2, Al2O3 is hard and non-deformable. It also plays havoc on refractory in the form of stickers and large macro-inclusions that can get entrained in the steel.

The other problem with lower Si steels is Aluminum efficiency and clean taps. Since a good portion of the oxygen from the blow remain in the furnace slag, if the heat tap is poor, then efficiency is bad, and you start with an unkilled heat. If the heat is tapped very cleanly, EBT for example, then efficiency can be really high, causing excessive aluminum to remain in the system. Having high aluminum levels in the steel is a detriment during processing since oxygen is introduced during the reheating process at the LMF, also during exposed stirring. This again leads to the formation of Al2O3. The later forming Al2O3 is considered worse than early formers since there is less flotation time and typically they form smaller inclusions.

So in conclusion, low Si steels are more difficult for steelmakers to produce. That isn't to say impossible, just more difficult. There are tricks of the trade that can be applied to ease the Al-only killed steels, but they must be learned through trials and some different refractory usages.

 

[TVP]

deadrange just provided an expert-level summary of the challenges to produce low Si steels. One method that some steelmakers use for producing clean steels (low inclusion levels) of this type is to perform vacuum degassing after ladle refining. During the vacuum degassing process the inclusion count can be further reduced by additional Ar stirring and slag interaction, while the dissolved gas content is also reduced. Mittal Steel's Gandrange facility (formerly Unimetal) and Hylsa in Mexico are two examples that use this practice, with some final alloying additions also taking place, including precise sulfur "dosing" in order to optimize the type and amount of non-metallic inclusions. Use the following link to find more information on the subject:

http://www.google.com/search?hl=en&q=vacuum+degassing+argon+slag+inclusion&aq=f&oq=

 

[metengr]

I agree as stated above. Well worth much more than $0.02, I would say deserving of a purple star.

 

[steelmtllrgst]

Please also note that many inquiries for <.10% Si also have a very strict Al maximum with the goal being to minimize B types in the "superclean" steel. Many ask for low Si and also <0.015% Al - leaving only a 0.005% range for Al in order to get just an OK deox.

These grades are difficult, but use of good secondary refining practice and experienced operators, they can be quite consistently achieved.

 

[stanislasdz]

A first thinks for ALL !

The member of the metal and metallurgy forum are my second family !! thanks for your advices

TVP, Arunmrao, Metengr, Redpicker..... and others you are very helpfful guys !

I will read and try to understand each answer

Arunmrao ; My sympathies too, you are a smart man, YES since few months ago i 'am in steel forging plant. Sorry i have betrrayed the steel casting !!! many thanks for your advices .....