There are a lot of things I know nothing about, and metallurgy is one of them. I know there is a lot of knowledge about that here on the Forum, so here is my question.
When I send rear end housings to the powder coating shop, they often pass them through their oven before blasting and coating them, to remove all the grease and stuff inside. I just got a pair back from them, and they still had the sleeves in them. I noticed that those sleeves were the easiest ones to remove that I have ever encountered. (They were stuck so badly that I had broken my sleeve puller on them before sending them to the shop, so I sent them on their way while I was waiting for a new puller.)
So I got to thinking that I might just leave them all in there to be baked in the future, before trying to remove them. Now I'm wondering whether that baking process will remove the hardening from the sleeves. The powder coating ovens get to about 400 degrees. Is that hot enough to remove the hardening from the sleeves?
Mike, I do believe that heating will take the temper out of them. When I was welding we always "baked" the welds at somewhere between 400 and 600 degrees to "stress relieve" the welds. Temps were dependant on the thickness and type of metal. I believe the thin sleeves will lose some of the temper and hardening. I would not want to use a sleeve that had been heated to the temp of a powder coat oven. Just my opinions as Im not a stress reliever or metallurgist. Maybe we have one that will chime in with a good answer.....
I would take the sleeves to someone who has a hardness tester (probably a tool and die shop or a heat treating shop). Ask around, I am sure there is someone near you who can do it.
They can probably give you some very good insight as to what you now have. I would also take some that haven't been heated.
I suspect you will be pleasantly surprised.
Buy new hardened sleeves, why even think about taking a chance on used sleeves.