Rear leaf spring u-bolt plates - what are they made of?

[animal]

Okay, I realize this is probably a good way to prove my ignorance, but the spring pack lower plates on my '56 Ford Fairlane need the shock hole welded up and re-drilled. I can't believe they would be made of cast iron, since they are put under a load so often, but I want to make sure before I ruin them for good. Any help will be greatly appreciated.

 

[Bamamav]

All I've ever seen were steel.

 

[animal]

These are apparently cast iron. I hit a spot on the edge with my wire feed and it just melted.

 

[Old Iron]

If it's cast iron, use a nickle rod to weld it.