We rely on heat treated metals in my line of business, so I have just about enough experience with it to be dangerous. That said, I'm certainly no metallurgist, so take what I say with a grain of salt.
Assuming it's a simple carbon steel, this would be what you're dealing with:
You're well below the eutectic at 600°F.
You're not crossing into any bizarre phase change realms.
If it's a
non-hardened steel that you're starting with, and assuming you cool from your 600°F back down in a nice slow process (like simply turning the oven off and letting the whole system come down), you should return to the exact same point you started from.
If you started with a hardened steel, all bets are off. You could re-temper the steel at 600°F depending on how long you leave it in the oven at that temperature.
Of course, if it's not a simple low carbon steel all bets are off. Stainless acts differently, precipitation hardened steel acts differently, exotic alloys always act differently, and of course anything not steel acts differently (some aluminum alloys I work with can be aged at temps as low as 300°F.)
Do you even have an oven that will get you to 600°F? That's a bit more than your typical Kenmore can do. I'd suggest a lower temperature and maybe not a huge dwell time & you'll probably be ok.