I agree with Mr. Madias: "The usual meltshop practice for aluminum killed steel is to ad aluminum first, then ferroalloys". The addition of a strong oxide forming element is the most commonly used method of reducing the oxygen content of liquid steel.

Use the Ellingham diagram to help you decide which of the following may be suitable (cheapest) choices for this. In a process route including a VOD (vacum oxigen decarburaztion), some industrial practices intend to reduce the alumin consume (and cost) by decarburization reaction but this require (at least) to adjust the initial oxigen content and to adequate the slag properties

I hope I understood the question. The order of addition is FeSi, FeMn and then Al, normally with a break between deoxidation. The last insert, usually in the ladle and has the strongest effect. FeSi and FeMn are designed to remove a large proportion of oxygen AL.

The usual meltshop practice for aluminum killed steel is to ad aluminum first, then ferroalloys

 Al is the last

Yes, the correct sequence of addtion deoxidizers into steel melt is from weaker to stronger deoxidizers. When Fe-Mn added, the Ar shielding gas is needed. If not, the Mn volatilization will be occured.

If you are using the Mn and Si primarily as de-ox, then you would add Mn-Si-Al. Yes, with a nice pause between for mixing and reaction.  The real trick is to end up with virtually zero residual Al.

If you are trying to make alloy adjustments for either Mn or Si, then those additions would come after the Al.  Once the heat is de-oxidized you will have better recovery and you can control the results of the addition better.

FeMn-FeSi and then Al.

I hope its good to develop our own practice by checking the few samples In LECO Gas Analyzer because deoxidation practice also depends on the Quantity of the liquid metal, In some Steel foundry  it is notice that making deoxidation in furnace (top purging 40%) as well as in ladle(60%).

I admit that I rushed to answer. In general, fair is FeMn, FeSi and Al. But the order depends on the steel grade developed and aggregated, ie inverter, induction furnace or EAF. There have been situations where I worked with the sense, FeSi, FeMn and then Al. Chemical composition of steel can determine the order of addition of ferroalloys. The question is rather general. Perhaps related to a specific brand may be another answer.

I would agree with Dr. Constantin Marta.

I agree with Mr. Madias: "The usual meltshop practice for aluminum killed steel is to ad aluminum first, then ferroalloys". The addition of a strong oxide forming element is the most commonly used method of reducing the oxygen content of liquid steel.

Use the Ellingham diagram to help you decide which of the following may be suitable (cheapest) choices for this. In a process route including a VOD (vacum oxigen decarburaztion), some industrial practices intend to reduce the alumin consume (and cost) by decarburization reaction but this require (at least) to adjust the initial oxigen content and to adequate the slag properties

weak to stronger 

Mn, Si and Al

Usually, aluminum first, then ferrosiliconmanganese

If you add first the stronger deoxidizer, there is no case in adding the weaker one. The proper sequence is first FeMn, then FeSi and finaly, Al.

I can see a controversy on this topic. To all of you I say, do not forget that FeSi has large concentrations of aluminum as high as 3%, sometimes. Therefore, adding first FeSi will produce very small alumina inclusions unable to float out all through the refining process.  The final steel will contain very tiny inclusions which will  hinder the cleanliness. Oxygen concentration after FeSi additions is usually well bellow the equilibrium with silicon due to the presence of aluminum.  Aluminum concentration in FeSi is the main reason to decide first Al or FeSi. Please make thermo calculations!

If %C in the grade is more than 0.1, then coke should be added first, followed by simultaneous addition of SiMn and FeSi may be done in order to ensure complex de oxidation. Such that MnO and Sio2 liquid inclusions may form followed by Al. As recovery of Al is lowest.

While all the above answers are correct in their sense. One should not miss the commercial aspect too. With ferro-alloys cost swinging a lot, there may be a condition where killing by one deoxidizer over the other can take precedence.

Then there is grade restrictions. For silicon killed grades, deoxidation first with addition of petcoke, addition of SiMn and then FeSi would be the ideal choice. However, if there is restriction in Aluminium, then FeSi addition should be carefully done as FeSi is known to have around 3% Al.

As a general rule of thumb within the technical limits use the less costly ferro-alloy first.