kverges
Enthusiast
This is sort of a general tech question, but this seems an active place to post, so here goes:
I have read and discussed cryogenic treatment at great length, but so far with no scientific discussion of the physics or metallurgy involved. FWIW, I have taken one course in solid state physics of solids, in which we discussed to some extent the physics behind alloys, heat treating, work hardening, annealing and other engineering practices and principles. So I don't think of myself as a complete ignoramus; just enough to be dangerous.
In all the situations we studied that involve transforming a solid via temperature changes, heat is required. The physical reason is that the additional kinetic energy (vibration amplitude) in the crystal lattice allows the atoms that make up the lattice the ability to migrate, change crystal structure, allow impurities to escape (like hydrogen), and so on. The item is then quenched (cooled quickly or slowly) to cease this activity and the material has a different physical characteristic (such as tensile strength, hardness, etc).
Perhaps the best example for an amateur scientist is the melting of sulfur. At room temp, sulfur is typically a crystalline yellow. It can be melted and forms a red liquid (cool for us nerds). If you pour the molten sulfur into water to quickly quench it, then it stays red and rubbery - so-called "amorphous" sulfur (if you don't believe me, you can do this at home pretty easily once you get some sulfur powder or crystals). Let that red blob sit at room temp for a few days, and it becomes crystalline yellow; the atoms have sufficient motion to rearrange at room temperature. Although I have not tried it, if you cooled the sulfur to liquid nitrogen temps or lower, I suspect that this transformation might not occur as quickly or perhaps ever, so long as the amorphous sulfur was sufficiently cold.
What I am getting at is that a cooled metal part (that had already sat at room temp for a long time) probably should not change structure as it cools (or is there a phase change of some kind at cryogenic temperatures into another form of solid?). The cooler the piece, the less vibrational energy of the atoms, and the less chance to rearrange. The ultimate extreme would be absolute zero, which by definition means the atoms are motionless and therefore no structural change would be possible.
So now that I have gone on ad nauseam, can someone scientifically explain how cryogenic treatment is supposed to affect the typical ferrous alloys that are treated? As you can imagine, my "smoke and mirrors" detector has been going off for a long time on this, but I would love to learn the error of my ways.
Keith
I have read and discussed cryogenic treatment at great length, but so far with no scientific discussion of the physics or metallurgy involved. FWIW, I have taken one course in solid state physics of solids, in which we discussed to some extent the physics behind alloys, heat treating, work hardening, annealing and other engineering practices and principles. So I don't think of myself as a complete ignoramus; just enough to be dangerous.
In all the situations we studied that involve transforming a solid via temperature changes, heat is required. The physical reason is that the additional kinetic energy (vibration amplitude) in the crystal lattice allows the atoms that make up the lattice the ability to migrate, change crystal structure, allow impurities to escape (like hydrogen), and so on. The item is then quenched (cooled quickly or slowly) to cease this activity and the material has a different physical characteristic (such as tensile strength, hardness, etc).
Perhaps the best example for an amateur scientist is the melting of sulfur. At room temp, sulfur is typically a crystalline yellow. It can be melted and forms a red liquid (cool for us nerds). If you pour the molten sulfur into water to quickly quench it, then it stays red and rubbery - so-called "amorphous" sulfur (if you don't believe me, you can do this at home pretty easily once you get some sulfur powder or crystals). Let that red blob sit at room temp for a few days, and it becomes crystalline yellow; the atoms have sufficient motion to rearrange at room temperature. Although I have not tried it, if you cooled the sulfur to liquid nitrogen temps or lower, I suspect that this transformation might not occur as quickly or perhaps ever, so long as the amorphous sulfur was sufficiently cold.
What I am getting at is that a cooled metal part (that had already sat at room temp for a long time) probably should not change structure as it cools (or is there a phase change of some kind at cryogenic temperatures into another form of solid?). The cooler the piece, the less vibrational energy of the atoms, and the less chance to rearrange. The ultimate extreme would be absolute zero, which by definition means the atoms are motionless and therefore no structural change would be possible.
So now that I have gone on ad nauseam, can someone scientifically explain how cryogenic treatment is supposed to affect the typical ferrous alloys that are treated? As you can imagine, my "smoke and mirrors" detector has been going off for a long time on this, but I would love to learn the error of my ways.
Keith
