Affects of extreme cold on metal?


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milcaztra
May 19, 2004, 01:19 PM
I know what the frig does to a Hershey's bar, but I'm curious about the affects of extreme cold temperatures on metal. I remember reading the comments of a custom knife seller that he had seen a top quality knife break in the Arctic. I've read about pistol slides cracking in cold weather.

So, for all of you metallurgists or engineers, does cold temperature make metal more brittle or more likely to fracture under stress? Would cryo treatment have any effect on the likelihood of fracture?

Thanks!

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Jeff White
May 19, 2004, 02:21 PM
I'm not a metallurgist, but when we were training up for Brim Frost 83 we received a lot of classes on how the extreme cold would affect our equipment. They told us that cold soaked steel could become ver rittle and shatter, but only when it was cold soaked. After it warmed back up to a reasonable temp that wasn't suposed to be a concern.

Jeff

mete
May 19, 2004, 02:39 PM
I am a metallurgist and your question depends on the metal.Back in the 1800s russian troops had buttons made of tin , the cold temperatures of the russian winter caused a crystal transformation which caused the buttons to come apart ! Cryogenic treatment will have no effect on brittleness of steel in cold temperatures. There is a phenomonen called brittle transition temperature in steel- below a certain temperature the steel becomes brittle .This is dependent on the chemistry.It is one of the problems of the steel of the Titanic which caused brittle fracture which lead to the sinking. This phenomenon is known today ,unlike in the past but I don't know if the gun makers take it into consideration other than the military.

milcaztra
May 19, 2004, 04:38 PM
Interesting. Ok, so let's say that the molecular structure of a steel changes or transforms at cold temperatures, depending on the type of steel -- composition and heat treat. If you apply stress to metal in this environment, the probability of failure increases. Most of us don't experience these kinds of failures b/c we don't stress our equipment to these extremes -- atleast I know that I don't. :D

If you stress metal repeatedly when it's extremely cold, would that be kinda like "cold working" it, causing additional crystalization of the structure and brittleness, possibly increasing the likelihood of failure even at normal temperatures? If so, how would you "reset" the molecular structure? I know that after using brass a number of times, the brass needs to be annealed to restore ductility. Would the same principle apply to some extent. I saw on a cryo site a while back that after deep cryo (-300F for 20 hours), the company ran the subject metals through three cycles up to 300F. I'm assuming that the deep cold may have created permanent changes in the steel's molecular structure, so it had to be softened by this pseudo-annealing process.

Thanks in advance for your thoughts!

BobCat
May 19, 2004, 05:20 PM
Mete is right, it depends on the steel chemistry and previous heat treatment.

This is not the place to give lectures but it may be the place to pass along references.

If you can find a book called Introduction to Manufacturing Processes by John A. Schey, all your questions will be answered. The original slim volume is preferred - Second Edition is too thick, looks like a textbook (because it *is* a textbook), and the original one is much more accessible and less intimidating. The ISBN is 0-07-055274-6.

An absolute classic is Steels: Heat Treatment and Processing Principles by George Krauss. ISBN 0-87170-370-X, published by ASM International (formerly American Society for Metals). This is another classic but not a quick read.

There is a great softbound called Engineer to Win by Carroll Smith, ISBN 0-87938-186-8. It is aimed at the Auto Racing community but has the answers you are looking for. It is old - look on bibliofind or one of those.

If you are anywhere near a University library, look for the Metals Handbook from ASM International. It is a multi-volume compendium but Volume 1 (of any Edition) contains a wealth of information on irons and steels, and it is accessible (technical but it is in plain enough language you will not have a problem).

On the Web, look at http://www.steelynx.net/ and dig around.

I apologise for going on at such length without answering your question, but I love this field and I think you will gain more by looking up some answers than by my giving you half-baked, over-simplified misinformation.

Purrrs,
BobCat

entropy
May 19, 2004, 06:07 PM
Ask the Russians, they're the experts!:evil: All my Mosins are quite hale and hearty, dating, 1899, 1916, 1940-something, and 1942!:evil:

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