How to repair porcelain/cast iron sink scratches

Question

This is an under the counter sink installation and I do not want to remove the granite counter top to remove and repair the sink. Please advise best process to eliminate srcatches, dull spots. Most repair services in my area advertise a polymer spray-on process? Is there anything better?

If this does not work, is it possible to cut out the cast iron sink and replace with a new surface mount sink. If so how do I cut out the sink??

Look forward to your reply.

Lou