I've heard that there's no such thing as truly 'stainless' stainless
steel...

In practice stainless means "Stain Less" not stain free. Some grades are
more "Less" than others.

Bill

Just a short note to let you know that non magnetic stainless steel
generally has an Austenitic microstructure and magnetic stainless steel has
a ferritic microstructure

you will also find that on some twin screwed vessels one shaft is ferritic
and the other is austenitic guess which one corrodes quickest

Regards

E