It depends on the specific material. There are many types of cast iron. I think turbie housins have a little more nickel than plain old grey cast iron, could be confusing it though. The nickel would make it easier to weld.

There are generally two methods for welding cast iron. The most reliable is to gently and evenly heat it up till it's just glowing, maintain that heat, weld it and then slowly let it cool. Either bury it in hot sand or control the cool off with the gas torch.

Another less reliable way is to do it cold. Butter each side of the weld with nickel before doing a full weld.

Can also be braised but that might melt in a turbine housing.

Pretty much, if you're not an expert welder it's unwise to try welding up something as valuable as a turbine housing.

Edit: You can always practise on a junk one...