You have a hammer right. How about a vise. It should be in a soft annealed state. The vise should get it close just closing it in the jaws. Then open the vise up a bit and place 3 pieces of about 1/2 round (bolts will work) 2 on one side on each end and one on the other side in the middle on the bowed out side, tighten vise slowly and you will see it reverse the bow. Go easy. and figure out how much spring back you get. Keep moving the piece and spacers, working it and you can straighten. If you have and anvil and a hammer you can use that. Get the piece tapped flat as possible with just laying on anvil. Then if not perfect lift one end with a spacer like the above bolts and tap the high spot. EASY. Work the curves. If you use some care and don't rush you can get it near perfect. Then the grinder and the files will finish the job. If it is just bowed and the steel is soft it should be fine. If it is bend bend like a 90 or something, I would do it red hot myself other wise to much work hardening if worked cold.