I haven't read through the whole thread yet, so this may already have been adressed:
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Originally Posted by Berlioz /img/forum/go_quote.gif
Ferrous metals typically contain a solid solution called austentite. This is one of the weakest, softest alloy phases of iron. If rapidly cooled, this solution undergoes a process known as Martensitic Transformation, which turns the austentite into martensite. For many applications, martensite has superior properties (increased tensile strength, increased hardness, increased conductivity), so cryogenically treated steels are often found in medical and military equipment.
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Err, I thought this eutectoid (as the name suggests) reaction occurred at high temperature only?
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It can occur at high temperatures as well. This is why some metals are heat treated. This reaction also occurs with a rapid decrease in temperature though. Just two different ways to achieve the same result.
I'm pretty sure this is somewhat incorrect. Martensite is formed by rapidly cooling a euctectoid alloy of steel form a temperature above the temperature of the eutectoid point. To understand this, (and why cryo freezing should not form martensite), you need to understand what happens when a eutectoid allow of steel cools normally. When above the 723 C, a eutectoid steel is 100% austenite, which is a close packed FCC crystal structure. When it cools to below 723 C, it seperates into a combination of ferrite and cementite (BCC structure, which is less densely packed) which is called pearlite, since when viewed under a microscope, the lines that can be seen from the way the ferrite and cementite algn looks like a pearl. However, if the metal is quenched (rapidly cooled from above 723C) rather than slowly cooled, the alloy does not have time to seperate into ferrite and cementite, and instead forms martensite, which is a stressed BCC structure that has lots of defects (extra atoms of carbon trapped inside the crystalline structure). Please take note that defects make a metal stiffer and more brittle. Martensite is an extremely stiff, and equally brittle material.
I am not sure of how cryo effects the process, but I'm pretty sure from my understandings that once a material has settled into ferrite+cementite structure, you can't jsut cool it more to get martensite, since you need to input more energy to get it back into an FCC structure (remember that martensite is formed because the metal cools faster than FCC can transform into BCC). HOWEVER, it may be possible that cryo freezing steels will cause it to
collapse into an FCC structure since an FCC is denser (and thus smaller, for same # of atoms) and since cooling something makes it shrink. (please note, this previosu statement was jsut a GUESS, I don't
know anything about cryo)
This may all be irrelevant though, since cryo-parts deals with non-ferrous metals.
To the OP, atomic vs molecular is just semantics (sp?) for metals, since as mentioned, alloys don't really have distinct molecules. I would describe everything above with either word, its obvious no one is talkign about quarks, although electrons and protons have a lot to do with all this (since bonding and crystalline structures have a lot to do with attraction of atoms, which is effected by protons and electrons). I'm not advocating one way or another (I hadn't even head of cryo-parts till i read this thread), but I'm just saying, your reason for attacking the company seems a bit absurd. It's jsut word choice, nothing more.
Sorry if this has all been said already, I only read the first 3 pages.
