Quote:
|
Originally Posted by 1983/300CD
|
Steel is a special material. It is one of the exceptions to rules just like water is. With that, let me go on.
"Today's cryogenic treatment is a further advancement of this metals-aging "secret" practiced by these old craftsmen."
I visited these sights and none of them seemed to be that of a respectable foundary. I think they are trying to sucker people out of their money.
This will take a while to explain so bear with me.
So hear is the deal. Steel is comprised of mainly carbon and iron (then manganese and other things, bla bla bla, I know.) . Threre is typically two differnt phases in the material. For this we will say alpha and beta (Fe3C actually) are the names of our two phases.
Now, the alpha phase will form a crystal structure. The beta phase, meh, not so much. Its more of that of a glass (liquid, ceramic, dirka dirka...)
Stress is applied to the material. The material begins to elastically deform, until it reaches is yeild strengh. Then this happens. A material plasically deforms by the propogation of dislocations. In other words, lines of molecules break, reform with another line, and pass this "break" on through the lines and lines of molecules. This happens easily in the alpha phase easily because it is in a crystal structure, and molecules slide over one another easier than the messed up arrangement of the "beta" phase.
So these dislocations propogate thought the material till they hit a phase boundary. They stop there. They build up the more that the material is strained. It gets to the point where there is this congestion of dislocations in the material that it resist dislocation movement more and more. This is called stain hardening.
More stress is applied and the steel strains further. The material finally reaches a point where it can no longer pass dislocations through it and the material becomes brittle. Brittle is strong, but not as forgiving. Cracks form through the material form, and the matterial fails. The end.
So the moral of the story. The smaller the grains, the quicker the dislocations become conjested, the stronger the material, the more brittle the material. Visa versa.
An example of large grains being soft is anneled copper gaskets, which they stick in the furnace, grains grow in size, and the material becomes more maleable. Large grains = soft
Sort of. This is where the misunderstanding occurs.
Now I will explain what is going on with the "cryo" system
The process is called quenching. I talked about this before in another post. This is nothing new. You cool the steel so quick that it can't form these two separate phases. Instead, it forms martensite. Martensite has a crystal structure that doesn't like crack propogation. I.E., it is brittle. (and strong) However, brittle matterials are unpredictable, therefore, hardly ever used in engineering. Glass is unbelievably strong....
... if you could cast it free of suface defects and cracks.
Ok I am done for tonight. I hope I was coheirent.