[El_Lloydeo]

Sounds like you have some gray cast iron. I personally like to weld cast, and I use nickel rod. Preheat is very important, but so is what you do with it ater welding. I have a tub of play sand which I will bury a hot freshly welded piece of cast in. Not a bad idea to heat up some scrap steel and bury it in the sand to heat the sand up too prior to welding your cast. When you cool your casting in the sand, it slows the cooling rate big time, thus making the casting a bit more ductile. Vermiculite will work too. I know a guy who has an old stove in his shop that he cools a casting in. He cranks it way up and turns it down 50 degrees an hour. He has never had one break. I have never had one break either using the sand.