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Can You Weld Cast Iron to Steel? The Surprising Answer!

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worker welding cast iron

Cast iron is among the most difficult materials to weld. It is not only hard, but also brittle and prone to cracking. This is why many welders shy away from welding cast iron. However, with the right tools and techniques, it is possible to weld cast iron to steel.

The key to welding cast iron to steel is to use a low-carbon steel rod. This will help to prevent the cast iron from cracking. In addition, it is important to use a welding rod that is the same size as the base metal. This will create a strong bond between the two metals. However, it is possible to weld most cast iron types to steel with the right tools.

If you are new to cast iron welding, you are in luck, as this article will take an in-depth look at welding cast iron to steel, the best tools and techniques for welding, and other related questions.


What Makes Both Cast Iron and Steel Metals Unique?

1. Carbon Content

The difference between cast iron and steel is the carbon content in each metal. For cast iron, the carbon content is around 1.7–4%c carbon, while steel has 0.05–1.7%. On the other hand, cast iron contains more silicon and impurities compared to steel which ends up affecting such things as shrinkage rate, melting point, hardness, ductility, weldability, and castability.

One of the easiest steels to weld is the low carbon steel, which is around 0.05–0.30% carbon. Medium carbon steel, on the other hand, comes with around 0.30–0.50% carbon, and it is quite hard to weld and may experience some cracking problems, necessitating a bit of preheating before working on it.

Among the hardest types of steel to work with is ultra-high steel, which comes with around 0.90–1.70% carbon. You can blame this on the metallurgical changes it undergoes when heated, which prevents it from serving its purpose.

As seen, the higher the carbon content in a certain metal, the harder it is to work with it.

Let's look at some of the basic types of cast iron:
  • Gray Iron: This is one of the most common types of cast iron, which is brittle with reduced elasticity, making it easy to crack, especially as it cools down. It may need preheating before welding.
  • Nodular Iron: Nodular iron is a cast iron that gains ductility from added alloying elements such as magnesium. It has reduced chances of cracking, which may reduce ductility in the heat-affected zones (HAZ), which are the areas next to the welded joints.
  • White Iron: This is similar to high-alloy cast irons as they are extremely hard and brittle, making them pretty hard to weld.
  • Malleable Iron: This is white iron that has been taken through heat treatment to gain more ductility. This reduces the chances of cracking, making it easily weldable. However, it may also require additional heat treatment to reduce hardness and maintain (HAZ) ductility.

2. Different Volume Changes When Exposed to High Temperatures

There is a difference between cast iron and steel in terms of expansion and contraction under different temperatures. In the case of cast iron, such as gray iron, there is no huge impact in terms of expansion and contraction, and if the temperatures are high enough, the metal will break.

On the other hand, steel will expand and contract much more than cast iron. In the case of welding cast iron to steel, the increased expansion and contraction will add some stress to the cast iron side and increase the chances of cracking.


3. Melting Points

Another difference that should be considered while welding cast iron to steel is their varying melting points. For cast iron, the melting point is quite low at 2,200°F, while steel comes at 2,600°F.


4. Impurities

Cast iron will come with several impurities, including free carbon, air gaps, sand, oil, sulfur and phosphorous, and grease. These impurities may cause some defects, such as porosity and hot cracking.

On the other hand, steel is way cleaner with fewer impurities.


The 8 Steps to Weld Cast Iron to Steel

Before embarking on welding cast iron to steel, ensure you have the right gear for the job. Let’s look at how to go about welding cast iron to steel.

1. Identify the Materials for the Job

Before embarking on the job, you should first choose the right materials. It is important to be aware of the nature of cast iron parts as you may be working on cast steel rather than cast iron. One of the more common types of cast iron is gray iron, but you may have some other kind of iron.


2. Clean the Metals

You can use an angle rider or sandblast, followed by a file to remove any remaining carbon or abrasive materials. Cast iron has several impurities that must be removed before working on the metal.

In case the cast iron metal has absorbed some oil, a flame torch or non-chlorinated degreasers can come in handy to remove the oil. Avoid using chlorine in any welding environment as you may create some poisonous gasses in case of an electric arc or gas flame.


3. Prepare the Joint

Depending on the cast iron you use, you must prepare the joint before you start working on it. You can use a hammer and chisel to bevel the cast iron side of the metal. This will avoid contamination of the porous casting with abrasives.

You can also prepare the joint through a die grinder with carbide burrs or use an angle grinder but avoid too much heat on the cast iron. You can then use a file to remove any abrasive material.


4. Preheat the Joint

Preheating the joint reduces any chances of cracking, especially as it cools down. The best temperature to preheat the metal is at 500°F; you can use welding temperature sticks to check the temperature. For the preheating, you can use either a flame torch or an oven for the job.

flame torch

Image Credit: kboyd, Pixabay


5. Weld the Small Beads Scattered Over the Joint

Even if you have preheated the metals, you cannot weld a continuous bead because the cast iron may absorb too much heat and fill with multiple cracks. You will weld 1-inch beads scattered over the joint.

Focus on the arc as one side is cast iron and the other steel, especially if you use oxyfuel for the job. It will allow for less heat to be added to the cast iron, which protects it from rapid expansion. It will also prevent large amounts of carbon from entering the puddle and offer more heat to the steel part of the metal, which has a higher melting point.

The best advice would also be to weld straight beads without weaving. Also, ensure that the traveling speed is fast while welding to avoid too much heat on the cast iron.


6. Peen Each Bead

This is the process where you repeatedly hit each bead with a small rounded hammer at medium force. It will counter the weld metal shrinkage, especially since one side is steel. This is even more important if you are not using filler-based nickel materials.

ball peen hammer on white background

Image Credit: Hanna Yohanna, Shutterstock


7. Preheat Before the Metal Starts to Cool Down

After welding, ensure the metals have the same preheating temperature evenly spread out. Check the temperature and, if necessary, preheat the metal.


8. Ensure They Are Well Protected

Ensure you cover the metal as it cools down to prevent the iron from cracking after the welding process is complete. If you used an oven to preheat, use it again to cool the metals.


Methods of Welding Cast Iron to Steel

TIG Welding

It is possible to use TIG welding to weld cast iron to steel. This will require the use of nickel rods, including ERNiFe-Cl. For this, you must ensure that both base and filler materials are clean. Mild steel rods such as ER70S-6 are not recommended as they have a high risk of cracking.

MIG Welding

Using the short circuit transfer method, you can also use MIG welding to weld cast iron to steel. The main disadvantage of this method is the high cost of nickel wire and additional gas for the job.

The best wire for this job is the ERNiFe-Cl wire, which will cost you upwards of $100 for a 900gr nickel spool wire.

Mild Steel Rods vs Stick Welding Rods

Mild steel rods pose a great chance of making your welded metals crack as they start as low carbon rods and end up with high carbon along the welding process. This will result in the metal shrinking, pulling, and cracking. Some common rods that pose a huge risk include E7018, E6013, and E6011.

If you choose to use these rods, the best advice would be to use them for smaller low-value projects.

On the other hand, if you choose stick welding rods, the material you use will influence the type of output you get. For best results, utilize the ENiFe-Cl and the ENi-Cl or the ENiCu. Steel rod ESt and the common welding rods are not good for the job as they do not offer much ductility, and they also shrink.


Conclusion

Due to demanding conditions for welding cast iron to steel, most people will not recommend it, but if you are willing to do the work, using nickel filler material will go a long way in seeing the job to fruition. Always preheat the metal to reduce cracking and cool it down slowly to ensure the welded parts hold. However, weld cast iron to steel for the best results while working on smaller projects.


Featured Image Credit: Strannik_fox, Shutterstock

Cameron Dekker
 

Cameron grew up in Allentown, Pennsylvania, a once-proud steel town on the Lehigh River, where he got a taste of TIG welding in his high school shop class. He holds certificates for Certified WeldingEducator (CWE) and Certified Resistance Welding Technician (CRWT) from the American Welding Institute. His interests include scuba diving, sculpture, and kayaking.