[MW:4530] evaluation of detrimental effect of straightening

Dear All

in my project a girder is fabricated from S355 K2+N(normallized heat treated for fine grain). after welding, a permanent distortion occured in it.

now distortion fixed with heating up to 300 c & hydrollic jack.

i know ,this temperature doesn't have significant effect. but how can i evaluate how much mechanical working affect on quality of plates & welds(especially on toughness & ductility& fatigue strength)?

another informations:

1- the type joint between web& flange is double bevel

2-thickness of web:20,thickness of flange:35

3-plate girder is used in primary frame

regards