you can't feel it but it has the appearance of a bearing race that is starting to go little fractures in the finish, looks like a lobe on a camshaft that's starting to wear off
did it come off an engine that sat for long period, or had water intrusion? You could try to polish it with some crocus cloth, it might remove the discoloration and give you a better look.
These cranks are hardened.-------They are part of a roller bearing set-up.------You can not buy O/S rollers if you grind it down.----Only a few specialized shops claim to repair outboards cranks.
Try polishing it with a strip of #600 wet/dry sandpaper that is wetted down with mineral spirits. If it polishes up to a mirror finish within a short period, use it.
