I have had really good results tig welding cast iron using AC and Aluminum bronze filler rod. ( thats ErCu-Al-A2)
But only on cast iron that does not operate at high temperatures like exhaust manifolds.
On those type jobs, there are better filler metals that more closely match the expansion and contraction of cast iron.
Nickel rods and even stainless have been used on exhaust manifolds successfully but those type parts can be a crap shoot.
This video shows a simple repair on a cast iron vise.
I have another repair to do where a larger vise cracked from someone cranking on a cheater bar and I will post that video as soon as I get it welded.