Start with the least abrasive substance. Semi chrome is good, but it can do the damage described, if rubbed too hard for too long. If the rust has penetrated the metal, there will be one or more pits. Short of grinding or another abrasive method, there's nothing that can be done about that. I have had some luck using bronze wool. It is softer than steel wool and does not tend to polish the metal unless a great deal of pressure is used. I would put a liquid or paste metal cleaner on the spot and use a soft cloth or Q-tip to work with, being very gentle. If that doesn't do it, you can go to the bronze wool, leaving the cleaner on the blade to prevent too much friction. It really takes experimentation because rust and its damage can vary.