Fenders are high strength steel. They're heated up all the time. Especially to pop out hail dents. Shrink stretched metal. Modern frames are hydroformed. They stick a tube of the steel in a mould. Pressurised water pushes the tub to the shape of the form. Ta-Da, frame rail. It's technically cold forged. Some frames have accordion crinkles along the very front. If it gets crushed its a one time thing on crash protection. It's not meant to be straighten back out. The entire rail needs to be replaced. I've been GM certified in frame repair. Nothing beats new. No matter how well you try to get it back that way. Close but not the same. If it was so, salvaged titled stuff would command more money. There's a difference and it can affect the vehicle. If a crashed vehicle doesn't bother you. That's ok to.