"Whatever heat treatments the
"Whatever heat treatments the material has already undergone in the manufacturing process to harden it are for the most part final. Any further chemical changes are going to be very unlikely, especially for the amount of time and temperature we're talking about.
I'd be more concerned with cyclic stresses... and cracking. Don't want to take the hot gear and dunk it in cold water. Let it cool slowly.
450F is probably the highest you'd ever want or need to go. I only throw that number out because I've had some problems with bearings getting stuck on a shaft in the wrong spot during installation. I started with heating them up to 250F, got them stuck. Heated them up to Lord knows what to get them back off, put them back in the oven at 300F, got them stuck again, etc., etc. I found it a lot easiear and in the long run better for the material to be a little more bold in the first place and get her done without a lot of beating and banging."