What is the steel in hydraulic pistons?

I was asking recently about the HF 12" slip rolls (1" diam rolls). The replies led me to believe that they would be too wimpy. Since I don't
have room for a bigger one, I'm going to make my own: beefy (2" rolls), but small (12", 40-45lbs). I don't think that I've ever rolled anything bigger than 12" & I have a neighbor with 36" rolls if I do.
I'm wondering if pistons from hydraulic cylinders would make good rolls. Specifically, how hard would they be to machine? Even if I find the right diameter, I would need to turn down the ends.
Is 2" a common diameter for hyd pistons?
I occasionally see cylinders at the dump, but not frequently enough to wait for. So, do you think that I could find some, somewhere?
Thanks, Bob
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