How to Weld Cast Iron (anyone can do it)

For a lot of people the thought of fixing old stoves is daunting because a lot of the old stoves used cast iron, and cast iron is difficult to weld right?

No, not at all if you know a few tricks.

First off let me say that just the other day I welded up some broken brackets on a 124 year old cast iron pot bellied stove, and it certainly was not the equipment. My welder is an AC only Craftsman buzzbox junk thingy that can barely hold an arc. And I do not have any cutting torches, just a propane bottle to solder copper joints with. And welding rod...who even said you need to go out and buy cast iron welding rod? Not me.

If you have to weld cast iron now and then, you can honestly just use 6011 welding rod. In fact I welded cast iron the other day with it. (6011 stick rod 1/8 inch)

The real trick to cast iron is not really the rod that is used (we are arc welding, which is really just a big spark plug that creates an electrical gap that is so hot it can melt steel. The rod is just a filler. Yes 6011 is putting mild steel in the weld, but it also is melting base metal so its flowing cast iron in as well). I would not cast iron weld a 1940 Allis Chalmers head back together, but some stove parts here and there...go for it. As I said, there is a trick, and it is to both pre-heat, and post heat the steel.

I heat the steel up I want to weld first, weld it, grind it, then heat it up with the torch when I am done. Then let it cool a bit...not getting it cold...just less intense then it was. Then heat it up with my torch again...but not as hot, doing that 3 or four times so the cast iron is cooled down slowly. Immersing the cast iron in sand will do the same thing.

I did this the other day on the mitten rail brackets on a pot bellied stove I am rebuilding. It had two broken brackets and about 2 hours worth of cutting, welding, grinding and drilling created 2 new ones that are indistinguishable from the 2 good ones. If when you weld, you do have pits or holes, use a little bondo or liquid steel to fill them in. In mild steel you can go back and fill them holes in then grind it flush, with cast iron though, limit the welding to the least amount possible.

Again...my method is not going to let you pass a cast iron weld x-rayed test I know, but it will get you by. Pre-heat-weld-post heat: that is the trick to welding cast, and yes with 6011 welding rod if that is what you have.

Interesting. Thanks!

Bop it?

LOL may try this with my mig welder ....

I also have welded cast iron with a very old AC only Hobart welder and unknown rod probably 6011. It can be done....... in a pinch. I have also welded cast iron parts with a TIG welder and used monel (nickel /copper alloy) filler rods along with a 400F preheat and cooling in sand with very good results.

The thing you have to remember is cast iron is very strong under compression and very weak under tension, an that it expands/contracts in ALL three dimensions AND this is important it expands/contracts at a different rate than steel. You weld it cold, it gets hot and expands and puts the surrounding iron under compresion (strong) it now has a bead of a different metal holding it together, as it cools it contracts (weak) and it's prone to cracking right next to the weld usually while it is still cooling.

So the preheat is very important the posses isn't as important you just want good weld penetration and you want to use a filler rod that has a similar melting temp as cast iron. I like nickle rod because it seems to flow better and that's what your "supposed" to use.

One other thing not all cast is the same some has bubbles in it practically all has sand in it and you never really know how it will act. Some cast iron welds well some is nearly impossible.