Removing Hydrogen by adding Nitrogen 3

[stanislasdz]

I have read somewhere that some steelmakers introduce nitrogen in the steel molten and after the vacuum refining process and degassing the nitrogen will form bubbles. The degassing of these bubbles take with them some dissolved hydrogen

1- Is that True?
2 -Anyone have some informations about this

Thanks

Stan

 

[steelmtllrgst]

Hi Stan.

There are many grades of stainless steel that have nitrogen added, and it is usually done AFTER degassing. The reason for this is that there is an equilibrium nitrogen content reached during degas and it is a waste of expensive nitrogen-bearing alloys to add it before and then remove by degas.

Hydrogen will be removed during degas whether nitrogen is present or not, due to lower partial pressure in vacuum treatment combined (typically) with either argon or nitrogen gas stirring.

Any gas bubbles (nitrogen gas injected, argon gas injected, or nitrogen bubbles formed by precipitation at vacuum pressures) will essentially have zero partial pressure of H and remove some hydrogen.

Hope this helped.

 

[EdStainless]

Yes, it is done to some extent. This is similar to the use of argon to de-oxidize after carbon reduction in stainless steels.
You need these bubbles to be as large as possible. The near zero partial pressure of H2 and O2 inside the bubbles will cause a driving force for diffusion of the gasses from the steal into the bubbles.

If you were using vacuum degas I would guess that you would bubble N2 first and then go to vacuum, but I don't recall.


= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[arunmrao]

Instead of nitrogen ,argon is more common. There is a booklet on this topic by SFSA " Gases in steel". Please check if it is still available. The idea of purging the argon gas is that they would be the nucleating centres for the dissolved hydrogen gas in the metal. As the argon gas rises up,it aso enables to raise the hydrogen gas to the surface.

Do it carefully,and always keep observing the surface for the bubbles, if you do not find one,it means the pressure is building up in the liquid metal. Just abandon and run for safety!


If you think education is expensive, try Ignorance.
- Andy McIntyre


_____________________________________

 

[stanislasdz]

Thanks guys

It was very helpfull !

Any others comments are welcome

 

[strider6]

have a look at this site:

http://www.steeluniversity.org/content/html/eng/default.asp?catid=1&pageid=1016899460

http://www.steeluniversity.org/content/html/eng/default.asp?catid=195&pageid=2081272018

hope this help u

s

Corrosion Prevention & Corrosion Control

 

[deadrange]

All:

A couple of key points I wouldl ike to add.

1) The Nitrogen being introduced after vacuum degassing will not help displace the hydrogen in the steel. At least not to appreciable amounts. Hydrogen would be removed to below 1ppm based on hydris testing after degassing operation.

2) Argon is typically the gas used in the degassing operation for stirring, for a few reasons.
a) Noble gas, would from any determinental compounds
b) Temperature is higher than Nitrogen. Fear is freezing off the porous plug.

3) Bubbles are important during the degassing operation. Well not bubble as much as the mixing action. In a properly running operation there is a rolling action where the slag and molten metal interface and NMI are retained in the slag.

4) Subsequent hydrogen pickup in molten steel is usually found through the refractories. Wet brick has been a traditional location for extra hydrogen in steel. Watch for unexpected hydrogen pick-up in first heats on tundishes.

5) Normal steelmaking operations the hydrogen in the molten steel will be somewhere around 3 ppm prior to degassing. After degassing somewhere around 0.8-1 ppm should be expected.

 

[stanislasdz]

Great forum and great guys
thanks all !