Yes, cast iron can be welded. It’s a little bit difficult task but not impossible. Considering the brittle nature of cast iron, there will be broken parts of cast iron. The only way to repair such broken parts is welding.
Considering the various types of cast irons out there, I will be mainly talking about gray cast iron. This is the most common in their kind.
Besides, the white iron is almost not weldable and the ductile iron is pretty rare to weld. However, you can apply most of the tips mentioned herewith other types as well.
I will talk about which welding method should be applied while welding the casting iron including a video demonstration. Since it is a difficult kind of welding, make sure to follow all the safety protocols like wearing your helmet, jacket, gloves, and so on.
Why It Is Difficult To Weld Cast Iron?
When you compare cast iron to wrought iron or steel, it is unique. They are enriched with high carbon content (between 2% – 4%). That’s the reason they belong to iron-carbon allows an enriched carbon content gives it the unique characteristics of hardness.
Because of the hardness of the cast iron, it is really difficult to weld. Welding cast irons induce tensile stress because of the several heating and cooling cause expansion and contraction in the metal. Instead of deforming or stretching, cast irons crack which makes it so difficult to weld.
A simple crack or if you break a vital cast component, it means you are losing thousands of dollars for the replacement parts. It’s a nightmare for most of the cast iron machine owners who don’t know how to weld it the right way.
Broken parts will get ruined even more just because of a simple wrong move. There is a hidden danger as well. Outside, it will look strong but internally it will remain weak.
There are two options available to you. You can either hire a professional cast-iron welding specialist spending thousands of dollars or you can start learning it yourself. This article will NOT make you an expert in this field, but it’s a good starting point to break the learning block.
Guideline For Cast Iron Welding
If you select the gray cast iron to go forward, you can follow this guideline. Decide first which welding process (TIG/MIG) you will use to weld the gray cast iron. As long as you use the correct filler material and welding procedure, you can use any welding process to weld it.
However, take consideration of the following issues while choosing your preferred welding process:
- Go for the TIG welding process if you plan to weld up a machined surface. The reason is pretty simple. MIG or stick welding will cause spatter which may damage the parts of the machined surface not being welded. TIG has no such problem of spatter!
- Keeping the extreme heat or cooling of the electric welding process to a minimum level is necessary for welding. To do so, many consider the oxy-acetylene welding as a pretty good option for the cast iron welding.
- If you have to go for the MIG and stick welding process, go for it with the right consumables. But you will have a crack in the end result if you use the wrong filler metal. And, don’t forget to wear protective leather welding jacket to protect yourself.
Vital Tips To Follow While Cast Iron Welding
After you have determined your desired welding process to go forward, it’s time to move to the next level. Following these tips will help you a lot when you start welding any cast iron in the real world.
- Clean The Cast Iron Surface
Run a test to examine whether the surface of the casting iron is clean. You can deposit a weld pass on the metal. There won’t be any porous if the surface is properly clean. If it is not clean, clean it properly.
Before you weld anything, all the castings should be properly prepared. While you are preparing it, make sure to clean the weld zone. There should not be any foreign objects, paint, grease, or oil present.
The weld zone may have entrapped gas as well. For a very brief time, apply heat slowly and carefully on the weld zone to get rid of that entrapped gas.
- Choosing The Filler Wire
You are very limited when it comes to choosing the filler wire because only a few of them can weld the cast iron the right way. You are very much limited to use rich nickel enriched (99%) filler wire. Not just they are soft and machinable, it looks like the cast iron and they cool slowly.
The problem is, the pure nickel filler is expensive. An affordable alternative is using filler made with 55% nickel& 45% iron mix. When welded, it also looks like cast iron.
- Deciding Pre-heat or Cold Weld
Pre-heating the cast iron is a good option, but some opinions are suggesting that you can apply minimal heat to weld as well. But you have to stick to the one approach only. You can’t change the option during welding. Why?
Well, as mentioned earlier, it’s simply because of the brittle nature of the cast iron. Besides, cast iron has minimal deforming ability. On the other hand, heating has a deforming ability on the metal always.
This is where things get complicated…
You will end up having crack or stress in the weld if one part of the cast iron heats or coos faster than the other parts. So, you have to stick with one and I recommend pre-heating. Why?
Well, pre-heating significantly reduces the above-mentioned effect where it leads to crack in the weld. Only pre-heating will ensure the whole component of the cast iron to change uniformly.
So, it’s no wonder when experienced cast iron welders only stick to the pre-heat. While preheating, make sure you don’t touch anything without wearing a pair of welding gloves. Here is a video showing how to preheat the cast iron.
Various circumstances like the size of your casting may require any such repair without using any pre-heat. If this is the case, make sure to keep the parts cool, but not cold. Keep the casting temperature up to 100 degrees F. the welds should not be more than 1 inch long. Allow the weld and cast iron to cool down as mentioned above. Don’t do anything radical like cooling with water to cool it down.
- Ensure Slow Cooling
Probably the most critical parts of welding cast irons. Don’t apply a rapid cooling technique like quenching the weld in the water or compressed air. So, how should you cool the weld?
The golden rule is ‘The slower the cooling process, the better the result’. So, you can simply put the welded cast iron into the sand to cool slowly. It takes time and challenging, but you will get a better quality result.
Sealing The Crack
In the practical world, there is a real chance of having tiny cracks even when you follow all the steps and tips. That’s just the nature of the cast iron. When your casting has to be waterproof, this is a major problem. Use the sealing compound to seal such cracks.
Without adequate preparation and extensive care during the welding and cooling process, you won’t get a quality result. There are no short cut methods when you have to get long-lasting welding results from cast irons. Be patient and follow these above-mentioned process and tips.