Cast iron? I could be wrong, but I don't think the flanges are cast iron. Cast steel maybe.Welding cast iron to steel is never a good idea, Below is a quote from a welding site listing the problem of welding a cast iron flange to a steel axle shaft,
Quote "The main problem with welding cast iron comes from its high carbon content. During the welding process, this carbon migrates into the weld metal and/or the heat-affected zone adjacent to the weld metal, making it hard & brittle. This is how Cast Iron gets its reputation for post-weld cracking." end quote