What you want Lanse is forged steel clamps.
The cheap C clamps you buy at the box stores or harbor fright is gonna be cast or malleable iron.
Puddles shows a beautiful collection of clamps below. Of course I know he has many more of them then that.
Vice Grip makes some good specialty clamps for welding. Here's one that you would use a lot.
The sliding type clamp that Puddles shows is my all time favorite clamp. I think I used Wilton clamps like these years ago.
I always wanted a set of these and finally bought 3 of them at a machine shop auction a couple of years ago. Two 12" and one 16".
These are Bessey - from Germany.
Dunno the brand but they are good.
Remember: Drop forged steel or cast steel VS cast iron or maleable iron? Iron aint even close to the strength of steel.