Creep in CRES 301 Full Hard

[NaikD]

All,

For ASTM A 666, (301 full hard), from -25 deg C to 60 deg C, I am wondering whether the material would be susceptible to creep as data for such low temperature do not exist.

I did extensive survey on creep. Creep is unimportant below temperatures close to 0.3 times melting temp (in Kelvin) which is about 500 deg C for BCC, body centered crystallographc stucture of 301 full hard. And we are no where operating around that temperature.

Can anyone support or refute?

Thanks,

- NaikD

 

[NickE]

No, creep is not a factor. Creep is the result of hightemperatures as you state.

However, it seems that you are seeing dimensional change over time. Is the material truly spring temper 301? if so, what stress levels are you seeing?

(or are you just asking for confirmation of your extensive survey?)

 

[metengr]

To add to NickE's post, AISI Type 301 austenitic stainless steel that is in a full hard condition is not BCC in crystal structure. The original crystalline structure for 301 annealed is FCC (face centered cubic) and upon cold working to harden will partially transform to martensite, which is a BCT (body centered tetragonal) structure, and not BCC.

To answer your question, creep deformation (time dependent permanent deformation) is not a concern at the temperatures you reported for this material.

 

[NaikD]

All,

Thanks for quick reply. I posted a question on Finite Element Analysis Forum under "Stress Strain Curve"

http://www.eng-tips.com/viewthread.cfm?qid=135761&page=1

Just wanted to confirm from experts here that creep is not a factor.

NickE,

Yes, it is dimensional change over 26 cycles from -25 to 60 deg C thermal cycles on a strip (fixed beam with central loading). The details are in the above link and I got some very good answers. The stress is 151 ksi and the material is in plastic zone on stress strain curve.

metengr,

I learnt something new here from you. I am glad that I did post a message here.

Thank you all,

- NaikD

 

[NickE]

How did you determine the stresses of 151ksi? Through FEA?

Do you have test reports for the strip you are using? My Sandvik book gives a yield strength range from 160-250ksi.

My experience with FEA of springs is that mostly the answers are close, but that real springs behave a little differently.

good luck

 

[EdStainless]

Stress relaxation is a big factor in highly strained materials. Cyclic temperatures or stresses can often result in changes that are unexpected. Normally these effects go away after a few cycles and then you can measure the real changes.

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Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[NaikD]

NickE/EdStainless,

The stress was determined by nonlinear FEA. The material is ASTM A666 (CRES 301 Full Hard) and according to the standard yield strength is 140 ksi and ultimate strength is 180 ksi. If I look at the stress strain curve, the elastic limit is approximately at 115 ksi.

Although the component experiences thermal limit cycles and plastic stress, correct me if I am wrong, I do not see any stress relaxation as the temperature limits are not very high. Since component is in plastic zone, the strains due to temperature limit cycling are nonrecoverable as long as the stresses remain plastic.

Thanks,

- NaikD