Mobile Bob pretty much got it all.
Cast iron, especially 'dirty' cast iron sometimes doen't take to grinding out Vee notches very well. It smears graphite and aluminum oxide into the weld zone. BUT that's a small place to be doing any arc gouging. The solution is simple. Don't grind it out, cut it out. Use a carbide burr in a grinder and it'll solve both contamination problems at once and do a better job of cutting a J groove.
Harold's Car Museum in Reno bought Rockmount Research "Jupiter A TIG" wire from me for that particular job. They pre-heated to 700F, TIG welded and peened with an air operated shot peener, then wrapped the head in a thermal blanket and left it for hours.
Always check for cracks with dye penetrant, or one of the home brew substitutes, after re-surfacing. "Magnetic Particle" and "MagnaFlux" operations usually don't work on welded cast iron. Nickel is not magnetic.
A cheap and easy crack check can be done (OUTdoors) by painting the part with white gas or lighter fluid, wiping the surface off quickly and spraying the part with foot powder. The pressurized can stuff. Cracks will show up in the white powder as dark lines.
