The problem with cast iron is that when you weld it, there is a really good chance that there will be heat related molecular changes in the material right around the weld, where things like carbide and graphite will separate out of the base metal. You can see this if you try to cut through the material with a hacksaw after welding it, it's as if the area is case hardened. The surface of the material hardens and becomes more brittle, so it cracks much more easily. Even if it doesn't crack immediately from heat caused differential stresses when the weld cools, there is a much higher chance of it cracking when stressed later.
One of the reasons for brazing is that much less heat is used, and it is typically not concentrated on the immediate spot that is being worked to the degree that an arc weld operation concentrates heat. So with brazing, you heat the whole area of the repair to at least 300 degrees, then play the torch on where you want to deposit material, dip the rod in flux (or use pre-fluxed rod) and heat to the point of the rod melting and sticking to the cast iron.
One of the challenges of brazing or welding cast iron is that the base metal typically also has at least some junk in it, and a few things I have welded with nickel-rod in the past had *lots* of non-iron ingredients (nickle, lead, etc.) which start bubbling up to the surface when you started melting the base metal. This problem, plus any oil that has soaked into the casting will cause you grief. Cast iron is a bit like a sponge, and absorbs a surprising amount of oil, diesel fuel, etc. So I have had to bake a couple of smaller items that I needed to braze, and then go over them with some flap wheels to clean up the surface, before I have brazed them. It wasn't about heating them to do the brazing, it was about burning out the junk, so much to my wife's consternation I broiled them in the oven for several hours (after opening some windows) to get rid of the junk. I have seen others throw pieces in a wood stove for several hours to do the same thing.
So after baking the casting, abrading it with abrasives to clean the surface, I have had 100% success with brazing cast iron peices, and then just throwing a welding blanket folded up to 4 thicknesses over it to slow down the cooling a bit. The silicone bronze rods I have used are a pretty hard braze material when they cool, so it's not as if they will easily wear down with a dirt contact attachment. I am sure it would wear faster than iron or steel would, especially if you are constantly running into rock, but it's not a soft repair such as soldering might be.
Just something to consider...
