I grew up around a shop in the 1950's where we heat-straightened frames all the time. The low carbon steel used before the 1980's or so doesn't lose much if any strength when heated to a dull red color. Just don't approach the melting point and you'll be OK.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!