It is a super cold tempering process that greatly increases conductivity and greatly reduces overall wear.

Its a process I have been following and reading about probably for three years now. The tranny Im rebuilding will be treated and everything else I can pull off the car when the tranny is swapped out along with all my valvetrain upgrades. Its not really a hardening process as much as a toughening process. The main characteristic Im after, however, is the reduced abrassive wear and reduced friction, which kinda go hand in hand but thats what Im after.

They use the process now a lot in tooling and more and more in high performance motor sports. You may already be familiar with it if you have bought high end brake rotors. A lot of them are now being cryo treated and the extension in life by way of the reduction in wear is amazing to say nothing of their resistance to warping.

You can google it and come up with a bunch of good information.

With respect to spark plugs, it does a similar thing. Keeps the conductivity of copper but gives them the overall life of something like Platinum.