I'm certainly no expert welder, but I've welded a few cast pieces succesfully, and had a few failures. Some guys who deer hunt here on our place gave me a 4" cheap vice about 20 years ago. A few months ago I was seriously abusing it and broke the back jaw completely off. I figured it was finished. Didn't even bother to vee out the crack - just stuck it back in place and make a couple passes with 308-16 stainless. So far it's held. I use it about every day.
My worst failure was a broken fire extinguisher bracket off of our fire truck. I took it to welding school with me and repaired it using the technique right out of the book. Veed out the crack, built a brick enclosure, heated it red with a couple big rosebuds, welded it with a torch and cast rods, then slowly cooled it in air slaked lime. A beautiful repair. Next class the instructer proudly held it up to show everyone what could be done if we followed the book. I thought I was really something. After class I dropped it in the back floorboard of my car and it fell in half. Never had the heart to tell the instructer about that. . .