RiverDave:
It's good to have another brother in the foundry industry. I'm a metallurgist/production manager at a centrifugal foundry in Indiana. I have been advocating the use of more sophisticated materials for use in impellers for a several years. At one point, I even gave one of the pump manufacturers (Chet's favorite) very specific written instructions including casting procedures for making a cupronickel impeller. They said the cupronickel impeller didn't work, which probably means that they didn't get the chemistry correct, and then gave up on the idea. The current crop of duplex stainless steels also seem to offer significant improvements over the 300 series SS which is currently used. Thinner, lighter, and stronger impellers are easily possible. This seems to be an area of pump technology which is mostly ignored by the manufacturers.
SteveM.