Heat it up....weld with low hydrogen and peen the ever living hell outta it.
I’ve welded a couple, but used a nickel rod. I’ve never tried low hydrogen on cast iron.
Other than brazing, a high nickel content rod is all I ever use on cast iron.
Just by it's nature, most all cast iron is under a lot of stress to begin with. That's why sudden changes in temperature create such havoc on it, much like glass.
