A few years ago, I repaired several cast iron pump impellar housings that were cracking around the footings. The first thing I did was to drill the ends of the crack all the way through with a 1/4" bit. Then I used a 1/8" cutting disc on a side grinder to dig out the crack, cutting in from both sides, creating a double bevel. Before welding, I would preheat the entire housing to approx 500 deg. F, and preheat the repair area plus a few inches until it was a dull red in color. In between passes, I would re-heat. I had a helper keep the entire housing hot (using a rosebud) the whole time. I used SMAW with an electrode called "Castalloy". I don't remember the manufacturer, but I've seen it alot down here in Louisiana.
After I finished welding I would bury the housing in a box of warm sand.
I made a steel box with a hinged top and a propane burner underneath to heat the sand. It's important to let the sand heat up for a couple hours before you put the part in as you want to be sure that any moisture has evaporated. I would leave the burner on for a couple hours after I put the housing in, and then let it cool off overnight. The only one that re-cracked was one that I rushed and did'nt remove the entire crack to begin with. It never pays to get in a hurry, especially with cast iron!
Anyway, that's not a very technical process, but it works.
Good Luck,
Tim
Not knowing alot about your situation is a handicap but I will offer you an idea I have used on some tough cast iron repairs.
Forum