I have a 4" cast iron floor drain cover that is corroding due to the salty water from when my water softener recycles.

How can I replace this drain cover? Do I have to replace with another cast iron drain cover? I'm afraid I'm going to have the same issue in a couple of years if I do. Can I use a plastic ABS 4" drain cover? If so, how do I make the transition?

I have 3 drains "routed" to that floor drain. Please see picture.