You don't want to reduce the nitrogen, it is the most powerful austenite stablizer in the alloy.
Now, if you are casting and have the nitrogen too high you can reduce it by bubbling Argon through the molten metal. I seem to recall that coarse bubbles work best.
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Corrosion never sleeps, but it can be managed.
Sorry that I had a bit of a sarcastic remark there, just couldn't help myself.
EdStainless is correct. Nitrogen is integral to this alloy. However, if you have added too much prior to casting, removal can be done through argon bubbling. I can't place the term "coarse" bubbles, but I seem to remember "slow and steady" as the terms I'd heard. (Large bubbles?)
While on this topic,can someone please let me know the Nitrogen bearing compounds that could be added to introduce Nitrogen during melting in an open air induction furnace.
Thanks a lot .
For an induction furnace that is open to atmosphere, nitrogen will be introduced into liquid steel from the atmosphere. You will have no problem dissolving nitrogen in liquid steel because the solubility of nitrogen in steel increases as a function of temperature. Nitrogen can also be introduced from steel scrap used for melting.
The solubility of a gas in liquid steel is proportional to the square root of the partial pressure of the gas over the liquid steel (Sievert's Law). Thus, 1 atm of air pressure over liquid steel will be a source of nitrogen and oxygen. There is no need to introduce nitrogen-bearing compounds. You will need to use secondary steel making practices like AOD or VOD to actually degas the melt and control final chemical composition
thanks for some basic preview that you've give to us, all your tips had been done in my comp. but some information i 've heaerd about flux material from uk that can controk\l Ni gas in casting product. because we always face by Ni rest in casting that it should be as duplex standard. is anybody there know the flux or material supplier connecting to duplex process?
thanks guys.
Dony (Stainlees steel engineer of mb group indonesia)
When I was a melting engineer in an electric arc furnace facility we used NitroVan (nitrogen impregnated vanadium alloy) to pick up nitrogen (for carbon steel). The metal was shrouded during casting (with argon) so little pickup was gained during casting. I don't remember there being a good recovery percentage on the NitroVan though. Another item, when I was the melting engineer in an induction furnace facility, we accidently forced air into a melt (nickel alloy) we were trying to control the nitrogen pickup on (argon was supposed to be forced in, blanketing the molten metal). The nitrogen content went from ~500ppm (normal, open air melting) to ~1000ppm. (With the proper blanketing we were able to stay <300ppm.) Proper shrouding during the teeming and casting process was also necessary to control the nitrogen pickup.
Coquette (Dony):
In your last post are you saying that you are seeing nitrogen pickup during your casting? If so, what kind of casting are you doing? There are certain methods that can be applied depending on the situation. Casting through a flux can indeed lessen the contact time with air but I'm not so sure about it modifying nitrogen content though it is entirely possible. Also, are you sure you're not getting a secondary recovery of nitrogen from a late addition?
In stainless grades the natural up-take/release of N from the atmosphere is no significant. If you are trying to add nitrogen and you need to hit a range you are going to need to do it using nitrogen injection.
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Corrosion never sleeps, but it can be managed.
I'm not very familiar with duplex steels, but for stainless the easiest way is direct nitrogen gas injection during refining - AOD or some type of lance. We have also used high nitrogen charge materials with varying recovery, but direct gas injection is much more controllable / predictable. We also have made some nitridable (is that a word?) tool steels that specifically had high aluminum contents (over 1%) to promote nitriding. As far as I aware, removing nitrogen can only be done through argon stirring, or vacuum degas.
thanks partners,
special to arunmrao , where can i get those specific material nitrovan? is it possible to our process because my comp . do the process by arc furnace 150 kgs? how about the step it should be fill to the molten metal? tempereature?
where is your last job experience? thanks guys
to others
how can i get the information the investment casting in all over the world? because i 've plan to make corporation for some our special order and also do research for specific material. a thousand honours for u all partners..
Coquette 150 kgs arc furnace?? Is it a lab furnace? My job experience? I am a foundry engineer with 20 years of casting experience. Now I run my own foundry.
US companies are directly offering these compounds to their vendors in India for introducing Nitrogen. I have no access to these proprietary products. Hence I had made a request in my earlier posting.
Coquette if you can become a member of SFSA or CDA in UK you can have information and professional assistance in your assignment.
