It's cast iron. There is a better repair for this problem. Grind the holes out on the arm and weld a tube with a 7/16" hole in it that hangs out the bottom about a half inch. Use a 7/16" bolt that goes through the center and drill a 1/8 hole in it for grease. Tap threads for a fitting on the top so you can grease it. Works great. I fixed two of them this way. Now you don't have 2 small spots that will wear out again, you have a whole shaft that is greased, that won't wear out.

Nice repair!