Cast iron is difficult to weld, but definitely not impossible. Typically the process will involve making repairs to castings rather than joining castings to other parts. These repairs can either be done in the foundry where the castings are made, or made for the purpose of repairing defects to the casting discovered after the part has been completely machined.
The most common type of cast iron used in welding applications is gray cast iron, but all types of cast iron can be welded. Generally, cast iron has a carbon content of between two and four percent, which is about 10 times the amount found in most steels. That high carbon content causes the carbon to form graphite flakes, with the graphite creating the characteristic cast iron appearance when it’s fractured.
When making castings, welders pour molten iron into a mold and allow it to cool slowly. The slow cooling process allows for the welder to create crack-free castings. This is perhaps the most important thing to remember during cast iron welding in Phoenix, AZ: the casting must be allowed to cool slowly, or at least kept cool enough at all times that the cooling rate is not important.
The critical temperature for most cast iron is about 1450 degrees Fahrenheit. At that temperature, certain conditions can arise that lead to cracking. The arc will heat the casting to temperatures beyond this level, but this is okay so long as the casting does not remain at that temperature for an extended period of time.
Here are a few other considerations to keep in mind during cast iron welding:
- Choose the right electrode: If you are going to machine the part after welding it, you should use a nickel-type electrode. You might need to alternate electrodes depending on the type of weld. For example, a single-pass, high-dilution weld will likely require a different type of electrode than you’d use for multiple pass welds, fill passes or root passes.
- Heating: It is typically preferred to preheat your cast iron before welding it. However, you can also successfully weld cast iron by keeping it cool.
- Welding with preheating: Preheating the cast iron before welding slows the cooling rate of the weld and its surrounding region. Preheat to anywhere between 500 and 1200 degrees Fahrenheit, but never heat to more than 1400 degrees Fahrenheit, as that will put the metal into its critical temperature range. Weld using a low current, and after welding allow the part to cool as slowly as possible, wrapping it in an insulating blanket or burying it in dry sand.
- Welding without preheating: When not preheating to the same extent, you should still raise the temperature of the material to about 100 degrees Fahrenheit, but no more than that. You’ll need to peen after welding with this technique.
For more information about the processes used during cast iron welding in Phoenix, AZ and the applications for which it makes the most sense, contact Metal Pro Inc. today.