According to RoyJ :
Depending on HOW OLD it really is, the frame could be good old mild
steel or some of the newer HSLA grades and may or may not be heat
treated. One thing to keep in mind is that trailers have been flexed for
a lot of miles. That adds up to a lot of work hardening, fatigue spots,
etc.

Does work hardening from flexing explain the angle recovered
from old bed frames? :-)

Enjoy,
DoN.
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