How to weld cast iron?

Welding cast iron can be problematic for welders due to a significant amount of carbon. Carbon content in cast iron is typically between 2% and 4%, with other elements such as manganese, chromium, nickel, molybdenum, copper, etc. However, having a higher percentage of carbon proves to be a nightmare for most welders as the above rate is ten times more than what is present in the steel.

It is pretty challenging to crack cast iron without welding as, besides the elements mentioned above, they also contain traces of sulfur and phosphorus, as adding impurities makes the iron stronger.

How many grades of cast iron are included?

How to weld cast iron?

Before going towards the steps, let’s know how many grades of cast iron are available.

  • Grey iron
  • White iron
  • Ductile iron
  • Malleable iron

These five types of cast iron are so identical that it is impossible to distinguish them from each other without a thorough analysis. Nevertheless, cast iron is durable and has been used for many years with high resistance to getting rusty.

What are the steps to weld a cast iron?

How to weld cast iron?

The steps include;

  • Determine the welding area
  • Using electrodes
  • Pre-heating before welding
  • Cooling down

Determine the welding area:

The process is quite complicated. It is harder to weld a rusty part than a shiny brittle one.

Joining two broken cast iron pieces through welding is not a good idea. Brazing in this regard is a good idea. Repairing the cast iron damaged part with welding is preferable, like fixing the cracked part or filling the hole in the cast iron.

What should you do to repair the cracked part of cast iron?

It is obvious to find the crack in the iron before repairing it. If you see a black mark as a crack, you will observe the piece of iron keenly. You can also smooth the surface so it shows the shot more clearly.

If you prefer to drill a hole, the act will prevent that crack from propagating. Drilling a little bit past the visible crack’s end is the most appropriate way in this regard. Using this method, the fracture will cease after reaching the hole. It lessens the possibility that a fracture on the other side of the hole will let the crack continue where it left off.

It’s improbable that the item will remain whole after being welded back together if the fracture ends aren’t drilled before welding. It can simply continue to fracture while you weld it or shatter it eventually. Until you reach the crevice at the bottom, grind down.

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Using electrodes:

Only some electrodes are made to weld cast iron properly, as most of them cool down quickly, so they cause cracks and do not join the broken part accurately. The best electrodes in this regard are:

  • Nickel-rich content:

The electrode is among the best and can join the iron, which is abundant in nickel. However, it is expensive and does not work on thick cast iron. But it has the excellent feature of not getting cool quickly.

  • For stainless steel:

Cast iron does not change its properties or harden like iron consumables when joined with stainless steel. It isn’t easy to employ since it does not considerably expand and contract during the heating and cooling of the fusion process. It produces a process that is machinable after welding.

  • Brazing:

We have two options for brazing bronze. We may use oxy-acetylene or a Tig welder. We can offer a solid sealant between two components that are trying to unite or in a crack. The two surfaces will be joined by brazing in this case without cast iron’s fundamental qualities being altered.

Pre-heating before welding:

Heat before welding is a better approach as it prevents cracking due to pressure. As it is hard to control the heat, you must have sufficient experience in this regard.

When iron is heated to 500 to 1300 degrees Fahrenheit, its internal stress is reduced. This allows the iron to be under the heat zone so that the cast iron will not crack due to pressure.

Measure the temperature frequently using the thermometer, most probably an infrared thermometer. But if you lack it, you can also determine the temperature with a keen observation.

Step 1: The color of iron changes according to temperature and represents the dull red color on heating up to 900 Fahrenheit, but in sunlight, you will not be able to see this change. A room with minimum light would be the best approach in this regard.

Step 2: Don’t be greedy; complete the work by boosting the heat flame. You must show patience and weigh until the iron becomes brick red or bright red at a temperature above 1300 degrees Fahrenheit.

Step 3: Heating a small welding area could be better as the pressure will crack the iron cast. You need to heat the whole part if possible. Otherwise, heat the larger iron region to bear the pressure effectively.

Cooling down:

Finally, you have to cool down the iron after the whole process. The process must be slow so that the iron will join appropriately. Never allow water or compressed air to engage with the welded part of cast iron.

It is a very time-consuming process. To get a perfect weld, it will be good for you to cool down the iron for 2 to 3 days. The best way to cool the welded part is to put it in the sand. Uniform cooling is required to achieve a perfect weld.

Some frequently asked questions

1.      Can you use a MIG welder to weld the cast iron?

We can use the MIG process in this regard, but it could be better for cast iron welding. For cast welding, an MMA stick is preferable.

2.      Why is it difficult to weld cast iron?

Heating other metals causes expansion, casting iron cracks down on the heating. So that is the reason behind the difficulty a welder faces while welding cast iron.

3.      What if we braze rather than weld the cast iron?

Welding is best for repairing the damaged area, but if you want to join the two broken parts, then brazing is preferable in this regard.

4.      What kind of metal is unable to weld?

Different alloys, including aluminum and steel, titanium and steel, and aluminum with copper, are impossible to weld due to their metallurgical properties.

Final thoughts:

In the above discussion, we have briefly explained cast iron welding. The method is complicated for an inexperienced person, but they can firmly weld the damaged part of the iron. Carefully read the steps mentioned above if you don’t want to confront any difficulty.

I hope you have enjoyed this informative blog.

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