Properties at cryogenic temperatures for CF8M material 1

[ballvalve1337]

Hello,

i want to do an thermal FEA with Ansys. Material is CF8M (1.4408). The Analysis require thermal expansion coefficient, thermal conductivity, elastic modulus and poison ratio at -196°C (77k)
Can anybody tell me where I can get these values? I asked Google but i cant find anything. ASME only provides material properties for "room temperature".

Thank you!

 

[metengr]

As a first cut, you can approximate the same properties from RT to -196 deg C.

 

[EdStainless]

Why not use standard 316 properties since CF8M is the case equivalent?
Search cryogenic properties of 316 stainless steel

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

At that low temperature 77k, the alloy will probably have a phase transformation from fcc to BCT (martensitic) which would change the thermal expansion coefficient (CTE). CTE could be decreased since BCT/BCC is less dense than fcc.

 

[EdStainless]

One issue with castings is the residual ferrite. If it has been well annealed to assure that there is no residual ferrite then the CTE going cold will be the same as for wrought product.
Try this:

https://www.nickelinstitute.org/~/m...opertiesofAusteniticStainlessSteel_4368_.ashx

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P.E. Metallurgy, Plymouth Tube

 

[Guest102023]

Ed,
You have touched on the most significant issue here. ASTM casting standards permit a quite high maximum ferrite content, such that physical properties like CTE will be variable through the allowable range. Not to mention that ferrite significantly impairs cryogenic fracture toughness.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[EdStainless]

In service the best way to handle this is first homogenize the castings, say 6hrs at 2100F.
Then the castings should be gently temperature cycled, say from RT to -200F, back to RT then to 1000F (for stress relief). I would do this a couple of times.
As for the OP question, data for analysis, he needs to make some assumptions.
The data for wrought 316 will be the best case possible.
The worst case? It might be real ugly.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

LOL. Since when did physical properties suddenly become mechancel properties in the OP? The OP asked for physical properties like TC, Mod and Poissons ratio.

 

[EdStainless]

The physical properties are what I am talking about. High levels of residual ferrite or a skew in chemistry will have significant impact on CTE. The Mod will be fine either way, as will PR, TC, and HC.

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P.E. Metallurgy, Plymouth Tube

 

[ballvalve1337]

Thank you for your answers. I am not only able to find cf8m properties at cryogenic temperatures. i am also not able to find ANY austenitic material propoerties at cryogenic temperatures.
Has anybody got an idea where to get 316 properties? A datasheet or something?

 

[metengr]

For austenitic stainless steel go to the Nickel Development Institute;

https://www.nickelinstitute.org/en/...eratures_MechanicalandPhysicalProperties.aspx

 

[moltenmetal]

This is a good question, and I admit I come to this discussion much less informed than most of the posters here.

If I buy a commodity, mass-market CF8M investment cast article such as a 3pc ball valve, should I expect that the caster has cared much about residual ferrite, or has done a post-casting anneal? I thought that residual ferrite in these cast materials was in there by design, as it is in some of the weld filler metals?

The other thing people sometimes forget about CF8M is its carbon content. To my knowledge, there is no CF8M/CF3M dual certified material available, unlike the F316/L material which is ubiquitous. Am I incorrect on that?

 

[metengr]

You are not incorrect. I have not seen dual certification of cast CF8M grades, as well. I found the residual ferrite varies with the cast material. However, the level of residual ferrite does not cause rejection for the applications I have seen. If necessary, the residual ferrite content can be specified for the application subject to agreement between the Purchaser and Supplier.

 

[EdStainless]

Ferrite control is one of the most common addition requirements that you see added to specs.
We used to buy CF3M casting to the CF8M mechanical properties, so I guess it could have dual certed, but never was reported that way. And to be honest what we got was CF3MN, they used nitrogen to increase strength and improve austenite stability.
Ferrite control is important for cryo service as well as for acid service. There are many weak acids that will dissolve the ferrite quickly (both castings and welds), fluids such as tomato sauces and orange juice come to mind.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Here is another source on physical properties among other valuable information in an interesting publication;
See page 23

http://nvlpubs.nist.gov/nistpubs/Legacy/IR/nbsir81-1645.pdf

 

[MagBen]

I was just wondering how the cryogenic data were generated. 316 (CF8M) and 304 (CF8) will experience a martensitic transformation at low temperature when exposing to strain at mechanical testing, 304 will have the phase transformation even without presenting any strain! Did people take this into consideration?

As for residual ferrite, it is not necessarily a bad thing. Sometimes it may be intentional to 1. eliminate corner cracking, 2. prevent weld hot cracking, etc.

 

[moltenmetal]

MagBen is onto what I'd heard before- that the ferrite content is deliberate to control hot cracking- same as with some of the welding filler metals. The detrimental corrosion consequences in the filler metals are mitigated by extra alloying constituents, but not in the cast materials- you want extra goodies there, you need a different grade.

 

[EdStainless]

The wrought materials will not transform when cold, unless there is residual ferrite or heavy cold work.
They will stay fully austenitic to LH2 temps. Our LH2 lines stay fully non-magnetic.
Castings have other issues as well, you need some ferrite on initial solidification to help prevent hot tearing but you also need additions to promote castability. You end up with a slightly different balance of elements, but when solution annealed you should be able to remove all ferrite, unless someone cheated on the Ni, Mn, N content. This gets harder with low C since C is an austenite stabilizer.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

See the link below. The broken tensile specimen of 316LN was transformed up to 26% of martensite at low temperature! i would expect more volume of phase transformation on 316 since 316LN has more N to stabilize austenite.
Link

I remember i read an article saying wrought 304 has a martensite transformation at low temp alone, while 316 does not, when no strain was present (unfortunately i couldnot find the site of the article). composition makes the difference, 304 does not have much Mo to stabilize austenite.

Lots of our Kovar alloy customers request to test martensitic transformation at -80C and -196C. we sometimes got 0-10% transformation at -196C, and I ever had a project to add a bit more carbon to prevent transformation without much effect on CTE. Invar 36 does not have this problem due to higher Ni content.

 

[EdStainless]

Yes Ben, when strained past yield at LHe temps it will transform.
The unstrained portions are still 100% austenite.
We have run ITER material, but the Ni content was much higher.

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P.E. Metallurgy, Plymouth Tube