turbine corrosion

[sampson240sx]

I recently got a turbo off a mitsubishi gs-t I found in a salvage yard. Its in great condition and the car had less than 100k on it. I took it apart and cleaned it up and found it had a little bit of corrosion on the exaust side of the turbine.  I tryed scrapeing it with an exacto-knife but its pretty hard. Anyone have any ideas of how to remove this?

Thanks much.