How to Weld Cast Iron with A MIG Welder: Comprehensive Guide

Cast iron, one of the most brittle types of metal on the planet gets every new welder into thinking, “can we weld cast iron?” Well, literally many of us have at least one time heard from someone that cast iron cannot be welded.

They basically refer to the fact that cast iron generally consists of an excessive amount of carbon content which can be even 10 times higher than most steels. Well, that’s true.

The main concern with cast iron is, if you’re not fully aware of the strategies and tactics which are certainly required in order to work with this sensitive metal, you can make it even worse or even ruin your whole project. So the question still remains,

Can Cast Iron be Welded or Brazed?

Well, yes you can. At least our title has already spoilered you that! Okay, so now that we know it can be welded, but there are still many things to consider.

Is Cast Iron Hard to Weld?

Certainly, and as we said before, it is one of the most brittle metals on the planet, and covers with a high amount of carbon. You need to be very efficient and conscious when you’re going to weld cast iron. In fact, there is a study that suggests you only have a 50% chance to successfully weld this metal due to the diversified types of other metals that are proportionately included inside its body. Two of them are iron and steel apart from carbon.

Difference between Weldable and Non-Weldable Cast Iron

There are basically four different types of cast iron. All of them come with a different range of difficulty in order to weld. In fact, two of them are completely impossible to weld. Let’s learn about four of them in brief:

Weldable Cast Iron

  • Grey Iron: This type of cast iron basically consists of graphitic microstructure. You can weld them, but it would be quite difficult.
  • Ductile Iron: well, this type of cast iron is a bit unique because you can usually bend them without possibly breaking it. They have a high amount of nodular graphite but you can usually weld them like that of grey iron.

Non-Weldable Cast Iron

  • White Iron: unfortunately, this type of cast iron is literally impossible to weld. It doesn’t consist of any amount and type of graphite.
  • Malleable Iron: similar to that of white iron, you cannot also weld this category. As the name suggests, the cast inside it has been transformed into a malleable structure so it may transfer its form again if you’re even trying to weld.

how to weld cast iron with mig welder

How to Weld Cast Iron?

Now, there are basically three ways to weld cast iron. You can choose either MIG welding or TIG welding in order to effectively weld cast iron. But in this guide, we’re going to learn about the MIG welding process since it’s the easiest and most effective way to weld cast iron. So let’s begin:

What are the Required Gears?

As we all know welding generally requires some tools and equipment to get started. Since welding is a fire intensive work, apart from having welder, electrode and other tools, you’re gonna need some safety gear in order to protect yourself from potential accidents or hazards. So we can divide them into two sections.

Personal Safety Gears

  • Welding Helmet: no matter what material you weld, you’ll need this helmet in order to protect your eyes and face from potential sparks and flames which are generated through welding metal parts. Besides, the helmet should include an auto-darkening feature meaning you can be able to precisely observe the process despite having bright light over the arc.
  • Welding Jacket: welding jacket will protect and cover your full upper body including chest and arms from fire and flames. Besides, wearing a fire-resistant welding jacket should be your first priority before initiating the process.
  • Gloves: welding gloves are crucial. Your hands and wrists at the closest body part from the welding area. So you should definitely protect them by wearing fire-resistant gloves.
  • Chaps and Kneepads: welding chaps are basically used to protect your lower body or legs from potential hazards and flames. Besides, you can also wear kneepads which are designed to make you feel comfortable working on different positions.
  • Respirators or Masks: welding generates an incalculable amount of toxic fumes which aren’t good for our body. In this case, wearing a respirator or mask is highly recommended.
  • Welding Boots: lastly, you got to protect your feet by wearing a standard fire-resistant welding boot so as to protect them from hot metals and sparks.

Essential Welding Tools

  • A MIG Welder: since you’re going to MIG weld cast iron, you’ll need a standard MIG welder which would consist of all the general functionality and power to effectively weld your material.
  • Electrodes: knowing the appropriate type of electrode to use over your cast iron is very critical just like knowing how to weld it. You see, electrodes can play a vital role since cast iron is very sensitive. An electrode with a combination of 55% & 45% of nickel and iron respectively would be a good choice.
    But if you want more precise and slow cooling electrodes which are best for especially welding cast iron, you should go for high nickel intensive ones. But they would be a bit expensive.
  • Filler Metals or Consumables: there are basically two types of filler metals that are used with cast iron. One is iron and the other is stainless steel. Iron consumables basically consist of a high shrinkage possibility which is why stainless steel can be a better choice as it never hardens and shrinks. But since stainless steel also expands its properties during the cooling and preheating stage, it is also a bit challenging to work with this material.
  • Shielding Gas: A ratio of 80:20 mixtures of argon and carbon dioxide is best for MIG welding cast iron. But since cast iron is highly vulnerable to rust, oftentimes using it also becomes worthless which is bad.
  • Welding C-Clamps: c-clams are very essential. They are basically used to firmly hold and secure your workpieces over your welding table so it doesn’t move aside during welding ensuring you a perfect weld.
  • Magnets and Sheet Metal Gauge: magnets can be very helpful when you’re trying to weld on different angles such as 90 degrees and 45 degrees. On the other hand, sheet metal gauge is used to measure the accurate size and thickness of the material you’re gonna weld.

Conditions Required For Your Workplace

A well-ventilated workplace is required to perform any sort of welding operation. This is because welding generates a heavy amount of fumes and gases which are very toxic and can easily mix with the air surrounding you making it unhealthy for anyone’s body to inhale.

The Step By Step Process to MIG Weld Cast Iron

  • Wearing Your Safety Gear: As safety is our first priority, we’re required to ensure this first. Just put on your wedding jackets and chaps and wear your welding gloves and boots. Besides, you should also wear a mask or respirator (if you have) before initiating the process.
  • Preheating The Cast Iron: cast iron should be sufficiently preheated in order to appropriately weld the metal. Otherwise, it will definitely lead to cracking over its body. You can do the preheating task by using your MIG welder.
    However, there are basically two approaches by which you can weld cast iron. One is called preheated welding and the other is called non-preheated welding.
    Generally, preheated welding is performed by heating the cast iron from 500 to 1200 degrees. This is the most effective and frequently used technique. At this temperature, the iron inside the metal gets stretched preventing it from cracking.
    On the other hand, a non-preheated welding approach is basically concerned with heating the iron up to 100-degree Fahrenheit. Lower to this temperature is definitely not recommended and you may certainly end up cracking the iron. The advantage of performing this technique is you can do it without using a torch.
    Lastly, using either of the techniques will require you some filler metals which are suitable for using over cast iron.
  • Preparation of Your Weld Metal: now this is very important, you need to adequately clean up your workpiece from all sorts of dirt and rust so they don’t lead to unanticipated contamination. You can use the angle grinder to do that. Besides, as cast iron is prone to cracking, you can drill a hole on the end of the cracks so they don’t get expanded.
  • Repairing the Cracks: apart from drilling on crack edges, you’re required to attach some cast parts over the cracks so that it works like a patch allowing you to weld with fewer concerns.
  • Clamp The Workpieces: you should clamp down your workpieces with your welding table or the surface you’re working on. This is very crucial because performing processes like welding can anytime dis-align your parts leading to a serious wrapping of your workpiece & ruin your whole project.
  • Welding Using Studding Method: now that we have come into the main process. We’ll basically use this method which is called studding in order to weld cast iron. This works by basically drilling holes inside the cracks and sealing them with patches like the way we’ve done before. Now weld over those patches with short welds (up to 1 inch) to effectively perform the operation.
  • Ensure Slow Cooling: this process is very critical because it duly reflects the accuracy and outcome of your welding. You need to allow the metal to get cool slowly in order to have the best result. Besides, you can also put sand over it for slow cooling.

Measures to Ensure Safety

Last but not least, having a fire extinguisher near your workplace will ensure overall safety throughout your welding operation. Besides, wind up everything after your work is done and store them in a clean area to use for the next time.

Final Words

Cast iron is one of the most difficult materials to work with. But knowing how to weld cast iron with a MIG welder can be a real challenge for any beginner welder. But we believe this guide would be helpful enough to get it done perfectly. Thanks for reading the whole post.

Stay along with us for our upcoming welding-related guides and articles.

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Gary Hargrave

Gary Hargrave

My name is Gary P. Hargrave. I started this website to enlighten and help train the thousands of potential welders out there on the nitty-gritties of this job. In this industry, I believe that passion is everything.

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