Corrosion on Sink Drain?

Not sure if this is corrosion or some sort of limescale? The drain is stainless steel. I think what happened was I used some sort of drain cleaner at some point and it got on the steel and I didn't wash it off. And now it's caused this to happen. Any cleaning tips? I've tried a brass brush to no avail. Hoping some sort of chemical cleaner to loosen it up? Thanks!

 

Are you sure that section isn’t copper? Looks a lot like copper corrosion.

 

The part that is still silver is stainless. The part that is corroded is most likely brass. I dont think there is much you can do without damaging the stainless. Wire brush is about all I can think of but try not to touch the stainless. It will slowly corrode again though.

 

That's what I thought - but the specs on the item does say stainless steel.

Looks like it'll just be easier to change the drain out. Well better to, not necessarily easier.