The Carpenter site provides the following (you do need to register, but it is free):
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Stress for rupture
Test temp 10 hours 100 hours 1000 hours
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800 [°]F/430 [°]C 142 ksi/979 MPa 117 ksi/807 MPa 91 ksi/627 MPa
900 [°]F/480 [°]C 109 ksi/752 MPa 82 ksi/565 MPa 54 ksi/372 MPa
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Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
The way to convert the data given by Corypad to room temperature is to use the Larson-Miller parameter:
P=(T+460)(log t + c) where c ranges from 17 to 23 and T is in farhenheit. Just extrapolate to room temp. I guarantee no one has measured room temperature creep for these materials.
israelkk;
The materials you are interested in will not have any measurable creep deformation at room temperature. The only deformation you will measure is elastic until the applied stress approaches the yield strength of the material and local slip processes produce permanent deformation.
Stress relaxation normally requires thermally activated slip, and I just don't see how this can happen at room temperature.
metengr
I agree unless the question was taking that into account. There is some infinitessimilly small amount of creep. It's hard to know in these forums the context in which the question is being asked.
My application is upto 90 Celsius. However, in actual test on mechanical springs made of Music wire or AISI 302 wire at spring temper for 7000 hours at 80000psi (yield was 261000psi) the creep was ~1% at ~80% of yield stress relaxation and creep will be ~6.8%. Extrapolateing to 20 years will give ~8.2%. Why Custom 455,465 will be different? can you comment? The stresses on the actual parts are about 70% to 80% of the yield strength.
israelkk;
Understanding the complete context of your question, the stress relaxation of heavily cold worked material (like the AISI Type 302) under constant load probably occurred from a mechanism similar to power law creep, instead of thermally activated creep. In this case, the application of constant stress in the heavily cold worked material (which contained an enormous amount of stored energy from cold working) promoted dislocation glide, similar to a thermally activated diffusion mechanism. I am not sure that extrapolation can be performed because as dislocation glide occurs, the amount of stored energy diminishes and I don't believe the creep deformation/relaxation would continue.
The reason I don't think precipitation hardened, martensitic stainless steel (Custom 450) would behave in a similar fashion (as heavily cold worked austenitic stainless steel) is that the precipitates from the aging heat treatment would prohibit this type of dislocation movement under constant load. In this case, thermally activated creep diffusion would be required to promote stress relaxation. These are just my own opinions.
You will most likely have to conduct specific creep testing, monitoring strain over time under constant load to obtain this type of specific data. The Larson Miller data is for creep rupture extrapolations not creep deformation data.
I am using the Custom 455,465 for a machined helical torsion spring. I have developed formulations based on tested cases reported on the literature which I use for relaxtion/creep analysis for long period loading of mechanical springs. Extrapolation is not just my idea, it was used in the literature to extrapolate fron a 7000hr tests to 100000 hours.
My formulation is mostly based on the data from Music wire and AISI 302. With no other massive information concerning other alloys I use those formulations for other alloys too. From your discussion about the difference between a cold worked case to just heat treated case I assume that using my formulation will give me quite a margin of safey and my design will be on the safe side. At lease I have a tool to estimate the worst case of relaxation/creep.
metengr hit this on the head.
I think that you are mixing effects here. Did you carefully tensile test the 302 spring wire? Had it been thermaly stress relived? Did you load and unload samples multiple times to the 80ksi level? Are you sure that there was no plastic deformation at this level? Did you test samples as springs or dead loaded wire? Most of what you measured was probably stress relaxation effects.
In a PH grade there will be very little residual stress after aging. This is a lot different than the situation with HCW302.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
I did not test any of those materials I am based on the work reported in the literature back in the 1950-1960 that was tested springs made of Music wire and AISI 302. The test were conducted at 20C, 150C and 250C temperatures. The stress were in the elastic zone and never abouve 67% of yield stress.
There is a phenomena with the hardening of 455 that may help with the problem.
If you severely cold work 455 the time required to precipitation harden is reduce by a least 75%, 1 hour vs 4 hours at temperature. Though not directly involved our group had very lengthily discussions with Carpenter concerning this phenomena early on during the introduction of 455. We were getting measurable dimensional changes over short periods of time in components made from very highly cold worked 455 that inadvertently been heat treated at shorter times than recommended. There was considerable work done on this matter by our group and Carp. There was a report put out and I have no idea of the distribution. The report concerned the low temperature movement of 455 after heat treatment. I do remember being told that it wasn’t totally stress related.
I don’t think I’ll have the report but will look.
At this times I was in discussion with Armco about the embrittlement of 17/4, unknown and not appreciated by anyone but me at the time.
