Just mild steel round bar. I don't think it's a big problem as the bends are so tight there is no place for them to open up, also, if I keep it lubricated there shouldn't be too much wear. If that becomes a problem I might have to case harden it, but I don't think that will be necessary.

A day without laughter is a day wasted- Charlie Chaplin
When wrestling a grizzly bear, you have to keep at it until the bear gets tired, not when you get tired.
1948 Chevy 2-Ton