Cast iron welding is always a game of dice. I don’t care who you are.

There are so many different grades things are made of and it’s not always obvious which one you’re about to weld.

There are ways to tell, like the spark test, but I have yet to see someone who can tell one type of cast iron from another by spark test.

So why is cast iron so hard to weld? Because it contains one metric ton of carbon. Consider this for a minute… Tool steels contain about 1 percent carbon and are considered difficult to weld due to over-hardening and even cracking problems.

Cast iron contains more than 2 percent carbon, and sometimes up to 4 percent. When so much carbon is present in iron, it hardens easily. But all that carbon has a purpose… it turns into graphite and that actually has a purpose as a lubricant on the cylinder walls of a combustion engine.

But for welding, all that carbon and graphite is horrible. Carbon in those percentages causes hardening of the weld metal and surrounding heat affected area. To make matters worse, cast iron is very brittle.

It doesn’t bend, it breaks. It can be good for engine blocks, but it’s hit or miss under load.

Return to the tig welding mold. What is the best rod to overcome the excessive amount of carbon present in the cast iron base metal? The most popular choice in arc welding rods seems to be nickel rods, also called ni rods. But tests have shown that for tig welding cast iron, aluminum bronze is a very good choice.

Aluminum bronze. yes you heard me these tig welding rods work great for tig welding iron castings.

Let’s see why…

1. Weld deposit will not harden due to high carbon content.

2. The solidifying weld metal does not have high shrinkage stresses that cause the metal to crack next to the welded areas.

3. Aluminum and bronze TIG welding rods are nearly as strong as steel.

4. When A/C welded, these Al bronze TIG welding rods flow and wet easily and achieve a minimal amount of cast iron base metal dilution. That’s always a good thing.

5. Aluminum and bronze TIG welding rods are much cheaper than nickel rods.

A good tip for using this rod for welding iron castings is to set the gtaw machine to air conditioning as if you were welding aluminum. This will allow the bronze filler metal to flow without mixing too much iron and carbon in the weld.

Try it. You’re going to thank me for this.