I think the best alloys mentioned in the article had an alphanumeric designation outside the 31x series, although 317 could have been one of them. “Duplex” sounds familiar, though. Very specialized, for when you really, really don’t want to see any rust. And correspondingly dear…
“Duplex 2205 provides nearly double the corrosion resistance typical in other austenitic stainless steels” (from the Best Stainless website). That’s one of the ones I remember reading about, perhaps the best one. I remember making a note to use it if I were doing a polished ss sculpture for a seaside location…