Can bent lawn mower blades be bent back to shape?

Someone borrowed my riding mower and returned it with the blade tips bent out of shape. Instead of being on a horizontal plane, they curl downwards rather severely at the tip. When I mow, it leaves a spiral shaped cut in the gr, a bunch of circles. Can I heat up the blades and bend them back to being straight? I have an oxy/acet torch. Do the blades need to be quenched in oil or water after heating them up? I happen to have a 5 gallon bucket that's full of used motor oil right next to the table vice and o/a torch. I've already priced a set of 3 new blades, they're about 70 bucks.