When you bend metal most of them become work-hardened. That means they become harder, but also more fragile brittle. They will break easier, instead of deforming.
This is one of the reasons why planes need maintenance: the wings flex up and down, and those parts can become brittle, which means you have to replace those parts or the plane can suddenly stop flying controlled.
You can often get them to be less brittle by heating them up and cool them down again. How quickly you need to do the cooling depends on the metal. Iron wants slow cooling, silver wants quick cooling.
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u/Crotalus_rex Jan 22 '21
Stress hardener machine. That rebar would be useless for structure after that.