Bar Keeper's Friend is your, er, friend if there's any rust or other nasties on the steel. It's oxalic acid based so after scrubbing off the rust and other crud with that and a scotchbrite pad the steel will self-passivate in a week or so.
Stuff dries out you skin something fierce, though, so you might better use gloves. I found this out after scrubbing down five NASTY kegs over a 6 hour period. Back of my hands felt like lizard scales for a week.