I'm not sure of the joint design or the grade of cast iron you're working with, so any suggestions would be subject to the alloy of the part your working with, any thing else would just be guessing.
In most cases I've seem, cast iron welding will not to stand up to thermal cycling, as in the case of a turbo flange, the best solution is to machine a mating part for the dissimilar metals and fasten together by bolting.
There are ways to weld parts like this, but you'd be well advised to have the particulars of both materials, and what each one needs as far as welding, before jumping into a welding project. Every cast iron takes different welding techniques and filler wire, just depends on what cast iron alloy you are dealing with.
Rouse