solution annealing of 304 Stainless Steel

[jiang1976]

Our vendor is planning to use liquid Nitrogen (in lieu of water) as the cooling method for the solution annealing of ASTM A240-304 Stainless steel cold formed head (2 heads). The head thicknesses are 49mm and 85mm.

Can we use liquid nitrogen as the cooling media?

 

[metengr]

jiang1976;

What diameter are the stainless heads? There is nothing to prohibit you from using liquid nitrogen as a cooling medium. This seems a little drastic to me, and I would be concerned about safety.

Why wasn't a water quench considered?

 

[jiang1976]

Thanks for you comments.

The vendor originally proposed to use water. I do no know the reason for the change.

the diameters are 2400mm (49 mm thick) and 4200mm (85 mm).

Do you mean it is techinically ok to use liquid nitrogen? is it possible to induce cracksof the 304 head during the cooling?

 

[metengr]

At 2400 mm diameter this is a serious safety issue in the shop (using liquid nitrogen will not induce cracks in this material, and is not necessary for cooling). Insist on using water quenching.

 

[arunmrao]

It is surprising to note that liquid nitrogen i being considered in lieu of water. Apart from safety issues,how is the economics being justified. I think there is something wrong in the thought process.

Small componnts,finish machined etc where value addition is very high one can consider exotic quenching methods,else stick to the basic practices.

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[jiang1976]

metrengr,

Thanks.

What kind of saty issues? Could you give me some examples?

 

[CoryPad]

One safety issue is splashing of liquid nitrogen. What is the temperature of the part before immersion? What is the ratio of part mass to LN2 bath mass? You can get violent motion of the LN2 when introducing a hotter part, even if it is only at room temperature.

Another safety issue is evaporation of LN2 can cause low oxygen conditions. The room will need to be appropriate for air flow, etc.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[EdStainless]

If they are going to blow very cold nitrogen gas onto the heads then it should work, provided that they do it uniformly enough to minimize distortion.
LN is a very poor quench. The cooling rates would be significantly slower than in water. The LN boils on the surface of the part and you end up with the part blanketed in nitrogen gas.

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[redpicker]

I suspect someone has things confused. AS EdStainless mentioned, LN2 does a poor job or heat transfer unless the surface is already very cold. You get a vapor blanket around the part and that seriously reduces the cooling rate. The object of quenching is not geting the material very cold, but to cool it quickly.

It would be much more likely that they are considering using a furnace that does not have water quenching capability (as in a vacuum furance) and are trying to back-flush with gaseous nitrogen for a quench. If so, you need to inquire about the cooling rates. I'm not sure what cooling rate is needed (some others may have better knowledge), but if they can meet the needed cooling rate, there is no reason it would not work. If they can't, you won't get a good solution anneal.

rp

 

[metengr]

For heads of this size, you need water quenching for an effective solution treatment.

 

[rmw]

Their water must contain some serious chlorides or other contaminants for them to go to this extent not to use water. Be careful.

rmw

 

[abassett]

I suspect redpicker is correct. Nitrogen back-flush in vacuum furnace sound more like it. Never a problem for me w/ thin section investment castings, but most of my 304 was 304L anyway, so the solution anneal was just a formality.