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cryogenic processed springs


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i need some AR magazine springs.  

 

For action springs I have had good luck with CS springs from sprinco and flatwire springs from Tubbs. So I checked both of their sites for springs and found both make a 17-7 flatwire magazine spring. I actually like the fact that Tubbs says it *can* hold more rounds in a magazine. I'm thinking that would make it easier to load a full 30 round mag on a closed bolt - something that might be very useful in competition.

 

Sprinco does cryogenic treatment on their flatwire magazine spring and tubbs doesn't. I can't find any definitive information on what exactly the advantages of cryo treatment would be on a magazine spring other than longevity ... but I don't think I could ever load and empty a magazine enough to wear out a regular 17-7 spring.

 

Does anyone know if there are additional advantages (or claimed advantages) of cryo treatment of springs?

If cryo treatment would aid in preventing spring fatigue of a constantly compressed mag spring I could see that as an advantage ...

 

 

 

 

 

 

 

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17 hours ago, emjbe said:

i need some AR magazine springs.  

 

For action springs I have had good luck with CS springs from sprinco and flatwire springs from Tubbs. So I checked both of their sites for springs and found both make a 17-7 flatwire magazine spring. I actually like the fact that Tubbs says it *can* hold more rounds in a magazine. I'm thinking that would make it easier to load a full 30 round mag on a closed bolt - something that might be very useful in competition.

 

Sprinco does cryogenic treatment on their flatwire magazine spring and tubbs doesn't. I can't find any definitive information on what exactly the advantages of cryo treatment would be on a magazine spring other than longevity ... but I don't think I could ever load and empty a magazine enough to wear out a regular 17-7 spring.

 

Does anyone know if there are additional advantages (or claimed advantages) of cryo treatment of springs?

If cryo treatment would aid in preventing spring fatigue of a constantly compressed mag spring I could see that as an advantage ...

 

 

 

 

 

 

 

I've had a hard time figuring out information about this topic too; a lot of the information seems to be from industry websites trying to hype up their product which makes me less inclined to believe their claims.  I know that LMT cryo-treats their barrels for all of their AR's.

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This isn't my specialty, but I studied some metallurgy in undergrad and went to grad school in materials science. I think I have a bit more than the curious layman's perspective, but not definitive knowledge on the topic. At minimum I know the terms to search for and can find unbiased commentary on the process.

In short, I believe cryogenic treatments are valuable to barrels designed to receive them. It doesn't work for every steel alloy, so don't send your existing barrel off to have it done.  The cryogenic treatment raises the hardness and strength of certain steels, which I think will contribute to longer barrel life assuming that the barrel isn't abused by mag dumps and allowed to get excessively hot.

With respect to springs, the cryo treatment in most beneficial for small stresses by increasing the stress limit at which no fatigue occurs. It doesn't seem to improve the cycle life of the spring if this compression limit is exceeded. I'm not certain, but I suspect that a fully compressed magazine spring is beyond the infinite cycle stress limit because our experience is them wearing out in 100's of cycles and not 10's of thousands. Someone who does more mechanical design probably has better insight on this though.


My opinion is based on a light reading of this dissertation The Effect of Cryogenic Treatment on the Fatigue Life of Chrome Silicon Steel Compression Springhttps://epublications.marquette.edu/cgi/viewcontent.cgi?article=1122&context=dissertations_mu

I summarized my understanding the research's conclusion in a cartoon of a S-N curve. The rate of degradation doesn't change at high stress loadings, but the threshold stress at which no degradation is noticed is higher after cryo treatment.  So maybe it makes the most sense for Production shooters who only load 10 rounds in 15+ capacity mags in the off chance that they're stressing their springs within that magic 35-30% UTS window that shows a difference.

 

fatigue.png

Edited by belus
added percentages to graph
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Tl;dr: Cryotreating may help the spring retain its initial tension over time, depending on alloy and heat treatment. It may also help fatigue life, as previously mentioned, but again depends upon the alloy and heat treatment.

 

Nerd answer:

Performing cryogenic heat treatments are for highly alloyed martensitic steels (or martensitic stainless steels). During the quenching process from the austenite temperature (varies by alloy composition, ~900°C), there is a phase transformation into martensite. This occurs over a temperature range known as "Martensite start" and "Martensite Finish" temperatures (Ms, Mf; respectively). For many alloys this range is several to tens of degrees Celsius, and the Mf is above 300°C for most low alloy steels. However, some alloys, this Mf is below room temperature (due to composition stabilizing the austenite), and you'll have some retained austenite that didn't transform into martensite. This retained austenite can undergo deformation induced transformation (mechanism for transformation induced plasticity, or TRIP). If you want it to fully transform before any service, as to not have distortion in service (perhaps important for barrels or springs), you want to finish the martensite transformation. You do that by getting below the Mf, which can be -30°C, so you put in liquid nitrogen after quenching. The time between quenching and liquid nitrogen cryotreatment isn't typically super critical, because the atom mobility is quite low at room temperature.

 

 

Edited by Benevolence
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On 9/10/2020 at 11:13 PM, emjbe said:

This is great information and specific answer of a 5% difference over time is great.


You might be reading that graph backwards. Sorry it was unclear.  The Y-axis is stress applied and the X-axis is cycles to failure.

It doesn't say that the treated springs apply 5% more force as they age. Rather, the critical force below which they never break is 5% higher. If the force is greater than this critical value there's no difference between treated and untreated springs. If the cyclic force is lower than the critical value for the untreated steel, then again there's also no difference.  Only in a very narrow window of stress does the cyro treatment offer any benefit for springs.

There may be more subtitles in that dissertation that I didn't appreciate, but I concluded that there wasn't much impact on spring life.

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thanks - i'm sure you were very clear and I just have some studying to do in order to understand more of the details, so thanks for the extra details.

 

I've ordered mag springs from both Tubbs and Sprinco just to compare them in actual use.  I'll be replacing all of my oldest (approx 10 year) magpul springs. If there's any notable differences in use i'll report back here.

 

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