Its difficult to answer with out the grade details however, some facts are as below
1. Heating to 400F will not cause microstructural change, grain recovery etc which help your bending process. There will not be any micro structure change due to age hardening temp is well above 400F.
2. Annealed condition is best microstructure for further cold forming. annealed microstructure will have all cold worked gains recovered for further deformation process. Based on the alloy grade , keep it above 770-800C ( UNS C17200- TS-200ksi) for 1hr for 1 inch thickness.
3. If you have cold word part then the grains will be elogated and further bending will cause cracks.