Welding cast iron is like playing golf. Because once in a while things go really well and that tricks you into thinking you’ve found the secret. But the next time you try, you’ll be presented with a new set of circumstances that make you realize you haven’t really found the secret. You were lucky.

The problem with cast iron is, in a word… Carbon… and lots of it.

So what about carbon? Carbon is the secret ingredient in steel that allows it to be heat treated to make really tough but useful things like: drill bits, razor blades, tools, and ball bearings.

I mean, just look at the ball bearings, they’re harder than a woodpecker’s lips, that’s tough! You get my drift… And if you’ve ever tried to solder a ball bearing to something, you know that soldering can be very brittle.

Let me try to put it in perspective. High carbon steel, such as ball bearing steel, typically contains about 0.6 percent to 1 percent total carbon.

Now let’s look at cast iron. Most cast irons contain at least 3 percent carbon, and sometimes as much as 4 percent carbon. For soldering, that’s a lot. And that’s without taking into account other problems like oil and exhaust combustion residue that are present in many cast iron welding jobs.

Cast iron contains so much carbon that it cannot be dissolved in the metal when it solidifies from the molten state. What happens in some foundries is that excess carbon is present in graphite flakes.

These graphite flakes are good for things like engine blocks and machine components because they actually lubricate wear surfaces like cylinder walls.

But all that carbon in the form of graphite makes welding really difficult. Any area in or around the weld that reaches temperatures near melting point and cools too quickly will be hard and brittle.

So what is the best approach? What is the best welding process? And what is the best welding rod for welding cast iron?

Lately I have had a lot of success using an unconventional method of welding cast iron. Are you ready for this?

I weld it with TIG in Alternating Current and with aluminum bronze contribution. I know it’s a bit off-beat, but here’s my reasoning.

*AC has less penetration than DCEN and you don’t really want to remove all the crap that’s in the cast iron, you just want melting.

* AC also allows aluminum bronze to be wetted better with less amperage.

* Aluminum bronze rod is stronger than silicon bronze and even a few fathoms.

* Shrinkage stresses from bronze to aluminum are much less than nickel rod and help prevent cracking in adjacent areas.

Regardless of which method you use to weld cast iron, a good hot preheat of around 500-600f goes a long way, as does cleaning the metal to a bright shine in the weld area.