How To Weld Cast Iron? Some Magic Techniques
Welding cast iron is a challenge due to its composition and special properties. So, people observed the critical situation of how to weld cast iron. You can weld cast iron successfully by using suitable welding techniques. During welding, you might face a high carbon content which is also a main problem of cast iron.
This carbon migrates into the weld metal or the heat-affected zone during the welding process. So, as a result, it is hard and brittle. Due to post-weld cracking, cast iron has earned a bad image. In this article, we will discuss the whole process of welding cast iron and also tell you some welding techniques.
What is cast iron?
Pig iron, which is used to make cast iron, is produced either directly from the molten state in which it is found or by re-melting it with significant additions of iron, steel, limestone, and carbon. It is prepared by re-melting with additives, after which several actions are taken to remove unwanted pollutants.
Why is it difficult to Weld Cast Iron?
Cast iron is difficult to weld because of its high carbon content. However, cast iron is not impossible to weld if you use the right welding technique. Using the correct temperature heat, welding technique, welding rods, and cooling down as needed can help to weld it.
Also by following expert tips and help can easily weld cast iron with minor difficulty. After some practice, you can become an expert in welding.
How to Weld Cast Iron?
Cast iron is one of the most difficult materials to weld that requires experience and significant steps. Here we discuss simple ways to weld cast iron by following these steps.
Collect the Materials and Welding Equipment:
Now, arrange in one line all the necessary welding equipment and materials you need for welding cast iron according to the welding technique and requirements. The following list of contents is as follows.
| Material | Welding Equipment |
| Required metal | Welding Machine |
| Welding Electrodes | Working Table |
| Welding Flux | Welding Cables |
| Shielding Gas | Welding Curtains |
| Cleaning Tools | Welding Tools |
| Safety Precautions | Welding Chart |
Wear the Safety Precautions:
First, wear safety protection to protect yourself from any accidents such as heat, burns, electric shocks, eye infections, and other damages.
- Wear safety glasses to protect your eyes.
- Wear long pants legs and long sleeves.
- Use a hood to protect the back of your head.
- Wear a tight-fitting, opaque welder’s helmet to protect your face from UV radiation.
- Wear gloves to protect your hands.
- Cover your head with a fabric cap.
Identify the Alloy:
First of all, before welding the cast iron must be analyzed and its types. So, there are several types of cast iron that have their special properties and require different welding ways.
| Type of Cast Iron | Explanation | Properties | Welding technique |
| White Iron | White Cast iron is formed when carbon in solution cannot solidify into graphite. | Hard (321-500)High compressiveTensile strength (200-410)High HeatResistanceLow Durability | Welding the white cast iron can be significantly more difficult because it cracks. |
| Grey Cast iron | Grey cast iron is found in castings known for its grey color and appearance caused by graphite fractures in the material. | Hard (156 – 302)Tensile strength (152 – 431)Yield strengthImpact resistance | MMA, MIG, gas welding, and SMAW are generally used to weld the grey cast iron with specialized nickel-based filler wires. |
| Ductile Cast Iron | Due to the metal’s round graphite structures, ductile iron is renowned for its impact and fatigue resistance, elongation, and wear resistance. | Hard (143 – 302)Tensile strength (345 – 827)CastabilityFatigue strengthAbrasion resistanceMachinabilityCompression | Successful welding of ductile iron produces mechanical properties comparable to those of the base iron. |
| Malleable Cast Iron | Malleable Cast Iron is quite similar to cast iron but has different properties. Cast iron fittings that are heated transform malleable iron to become a far more robust material. | Hard (110 – 156 (ferritic)149 – 321 (pearlitic & martensitic)Greater ductilityTensile strength (276 – 724)Elasticity | Welding malleable iron fittings will require special weld rods/electrodes to obtain acceptable weld metal and results. |
Inspection and Preparation to Weld Cast Iron:
Clean Cast Iron: Before welding, clean the surface of the cast iron by using any soap or detergent, and chemicals do any oils, dirt, or anything that remains.
Examine the cast iron: Check the cast iron for cracks or signs of damage. Use the NDT method to check for hidden defects to make sure.
Heat and preheat Temperature: Choose the correct heat temperature for welding cast iron because if the temperature is too high, you will heat the surface much faster than the metal underneath. The result is that it cracks.
Welding Rod: Choose the ideal welding electrode, flux, and filler wire for your welding procedure. Also, choose the right welding rod for your cast iron type.
- 99% Nickel Rod
- Steel Rods
- 55% Nickel Rods
Welding Machine: Set up your welding machine according to weld cast iron requirements. Make sure that all the wires of the machine are properly set and working at a great level.
Examine the Welding machine: Before starting up examine the welding machine that it works in good condition without any sign of damage.
Heat and Preheat the Cast Iron:
The most crucial aspect is that casting iron is best welded with extensive preheating. But keeping cast iron cool—not cold, but cool—is another technique to efficiently weld it. But once you decide on a course of action, follow it through. Keep it warm or cool, but don’t switch the way in the middle of the process.
- Hot Welding: Suppose that one part of the metal heats or cools faster than the other part of the metal then the chances of cracks and stress happen. So, it is better not to use more heat in the component because the cast iron has the factor to change once the temperature is over 1400°F.
- Cold Welding: A cold method of welding cast iron helps to reduce the temperature so that cracks and strong welds are not likely. However, in this process, internal strength remains poor in cold welding.
| Type of Cast Iron | Max inter pass temperature | Min Preheat temperature |
| Gray | 650°C (1200°F) | 315°C (600°F) |
| Ductile | 650°C (1200°F) | 21-315°C (70-600°F) |
| Malleable | 650°C (1200°F) | 21-315°C (70-600°F) |
Use the Welding Techniques:
Many welding techniques are used to weld the cast iron. These techniques are used according to the requirements and the condition of the cast iron.
SMAW:
- SMAW is also known as Sticking welding which is mostly used to weld the cast iron.
- To create the electric arc that uses a consumable electrode coated with flux to weld.
- Cast iron-covered electrodes, copper alloy electrodes, and nickel alloy electrodes can be used depending on the application. But nickel alloy electrodes are mostly used according to their matching color and thermal properties.Â
- Preheating is important to reduce cracking by at least 250 °F. Also used to control the cooling rate.
MIG
- MIG or GMAW welding techniques are also used to weld the cast iron.
- To protect the weld pool, use the nickel-alloy filler metal wire and an 80% argon / 20% carbon dioxide shielding gas.
- For beginners, it is not suitable to use the ERNi-1 for MIG welding when the ERNi-1 contains pure nickel.
- To avoid cracking, proper pre- and post-heating are necessary.
Oxy-Acetylene Welding
- This welding is a fusion welding process that is mostly used for repairing and dealing with small pieces of cast iron.
- In the welding process, it uses a flame created by the combination of oxygen and acetylene gases.
- For oxy-acetylene welding of cast iron, both copper zinc electrodes and cast iron electrodes are appropriate.
- Avoid the white iron and silicon loss development when welding with acetylene by preventing cast iron oxidation.
Finish Process:
After completing the process of welding, ensure the several steps.
- Give the cast iron some rest to cool down.
- After cooling, use a brush to clean off any slag or scum. Also, clean the place where welding was done.
- Make sure there are no cracks or defects. Remove cracks by re-welding.
- Apply coating or paint as required.
Our point of view
Cast iron is not impossible to weld but using the proper technique to suit your weld. We have discussed the entire process of welding step by step. So, follow every instruction carefully if you want to weld cast iron indoors activities.
You can also take the help of a professional. They will recommend and suggest to you because they are trained. You can achieve good results by using the proper welding process, filler wire selection, and experimenting. However, with a practice or two you can weld cast iron like an expert.
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