The best method of getting aluminium into solution in Cr/Ni/Fe alloy? 1

[dacf]

Hi, I am conducting a project in dimensional control of investment casting. I wonder if anyone can help me with the following:

What is the best method of getting aluminium into solution in a Cr/Ni/Fe alloy using an electric induction furnace? I am gaining good yield just by adding pure Al to molten bath, but some aluminium appears to melt on contact and remains as a film on metal bath surface. After removing any slag this is very difficult to remove. This surplus Al appears to cause casting inclusions as it oxidises readily.

It is not a solubility problem as I have achieved a higher % of aluminium in solution previously.

Any Ideas?

 

[unclesyd]

Can you add one of the Nickel Aluminides?

 

[EdStainless]

How much Al are you adding?
You really want to be as cold as possible when you add the Al. You will gain some temp due to the exotherm of the Al burning the residual oxygen out of your melt. You also want to have enought headroom on the temperature to allow you to go to full power after the Al addition in order to get effective EM stirring. You may want to add a portion of your Fe or Ni after the Al. To cool the bath and to help physically cover it.
If you are not using another deoxidizer first, and an argon melt blanket, reliable recoveries will be hard.
I used to add 7% Al to Co based alloys.

What size is the furnace? What size and freq is the power?

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Corrosion never sleeps, but it can be managed.

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

 

[arunmrao]

What percentage of aluminium in the melt are you aiming. If it is low add it while tapping the metal. Furnace additions produces a dross layer which is difficult to skim. Also due to oxide forming tendency of Al,the metal is sluggish and it is difficult to get a good and clean surface on the casting. Try to pour small quantities as fast as possible .

 

[mcguire]

These melts, if they are manganese/silicon deoxidized, have several hundred ppm of oxygen. This will all form Al2O3 after your aluminum addition. Removing this requires floatation. We used to bottom bubble argon through the melt in a large ladle to get good removal. You must not expose the surface to oxygen or nitrogen or aluminum will form a slaggy compound with these rapidly.
For maximum recovery, first deoxidize with some sacrificial aluminum. Let the oxide float to the slag, then add the amount of aluminum you need as coated Al wire through the slag, and you should get 90+% recovery.

 

[rd400guy]

Also, be aware that high aluminum grades are "gummy" during pouring. We make PH 15-7 Mo with 1.10% Al, and we teem through a nozzle 5mm greater in bore than any other grade we make. It is very gummy during teeming.

 

[mcguire]

Calcium treatment helps the nozzle clogging problem by making a calcio-alumina oxide which is liquid at pouring temperatures.