Effects of Burn Marks Due to Grinding

The biggest problem is that the "burnt" areas have been locally hardened and will not respond to thermal and mechanical stresses in the same manner as the "clean" areas. This may not be a problem but I do not know how your products are being used. Suggest that you add coolant flow during grinding to keep part temperatures relatively even (it will also help control "dust" and metal metal filings (which can be removed with a magnetic plug in the drain pan or the return piping).

I agree with previous comments, but one more thought. Depending upon the severity of the "burn" it could cause a localized stress riser resulting in a broken ring when installing. It's best to add coolant and not push the grinding operation beyond the thermal limits of the metal being ground. An old German engineer I once worked with had a saying, "Frist there is tight, and then there is broke".