It depends.
If it's not too bad and just some very shallow pitting, a buffing wheel can sometimes get it out, given enough time.
There's also re-graining, which is basically sanding down the metal, but it is very time consuming. Basically, you start with a course grit, sand in one direction, then switch to a slightly less-coarse grit, and sand in a perpendicular direction (to your original direction), then go to the next grit, and switch back to the original direction--and keep doing that all the way down to 1500 grit, and maybe finish with some buffing at the end.