A question that comes to mind in considering steel piers for underpinning your concrete slab foundation is “are they going to rust or otherwise corrode?” Fair question. One of the answers involves using galvanized steel piers.
Another method of corrosion protection for steel piers makes use of powder coating technology.
However, there is a report from the National Association of Engineers that questions the need for such protection for steel piers. The point raised is simple: get a few feet underground and there simply is not enough oxygen available for rust to develop at a fast enough pace to be a concern for the homeowner.
I ran across a couple of websites that talk about this report. You can read it here or here.
As I’ve said before. Opinions vary. On just about everything.