Manufacturers suggested name is seat ring; material is stainless steel with stellite
NSN 6150-01-462-0827
NSN 5905-00-931-3808
NSN 5990-01-544-4360
NSN 6645-01-562-7154
NSN 5975-01-277-1617
NSN 6620-01-035-6501
NSN 6650-00-403-6386
NSN 6110-01-515-2720
NSN 6150-00-184-5523
NSN 5975-00-752-7644
NSN 5960-01-599-9821
NSN 5910-00-448-1361