Are the scorch marks actually black carbon? If you rub it with a piece of white cloth or paper towel, does it smudge the cloth?
The steel will discolor from the high temperatures you'll get when you heat a pot without water in it.
If you make sure there is always some water in the pot, it can't get any hotter than it did when the food that came in it was processed.
If you're worried about it, set your oven to the highest temperature possible (over 500) and bake the pot in it for a couple of hours. Then scrub it out with a steel wool pad to remove the coating.