How to Weld Cast Iron – The Ultimate Guide for Welders

How to weld cast iron guide for Beginners

I have seen many welders looking for a guide on how to weld cast iron like a proIt is an exciting subject because repairing the worn out parts and fractured pieces. This process takes expertise, and a single move can ruin everything.

So I have written a complete guide that would be helpful for you in dealing with the cast iron welding process. You would be able to comprehend the necessary method and ways to get this job done in a detailed manner.

So at this point, we all know that the cast iron is brittle in nature due to carbon content in the mixture causes the metal to shrink and crack when heated at a certain temperature. Because of this factor, much care is required to weld cast iron. For welding cast iron, it’s essential to account for pre & post-heating preparation, heat management while welding and rod selection.

You should understand that there are various kinds of cast iron, so to weld it, you should consider the condition in which it is welded like for machined surface, the best option to weld would be through TIG.

It is favoring to preheat the entire casting part to prevent residual stresses that can lead to cracking. The best rod to weld cast iron is the selection of the type of rod that suits the application.

Choosing the Right Welding Rod for Cast Iron:

Use of 99% nickel rods:

These nickels based are often expensive. 99% of nickel rods produce welds that are machinable and works best on casting with low or medium phosphorus contents.

Use of 55% nickel rods:

These are cheaper compared to 99% of nickel rods and are economical. They, too, are machinable and used in the repairing of thick sections. It has a lower coefficient expansion than 99% rod, so fewer fusion line cracks.

Use of Steel rods:

Steel rods are the cheapest option and best used for simple repairs and fillers. They are not machinable and produce hard welds, requiring some extra grinding to finish. These rods also have benefit as this rod is much more user-friendly when arc welding and through this welding can be done on surfaces that are not entirely clean before welding.

Welding of Grey Cast Iron:

Grey Cast Iron Welding
                                                           Image Credits: Kyle Levesque

You might probably hear it can you weld cast iron, well the answer is, it depends on the type of cast iron as well as on the condition in which it is welded like for machined surface, the best option to weld would be through TIG. MIG and stick welding not preferable as the spatter produced from these may damage parts of the machined surface not being welded while TIG doesn’t have spatter issues.

But MIG and stick can be desirable by using the right consumables in maintained conditions; if not, then wrong filler metal can cause cracking, so it is necessary to choose the right filler for welding of cast iron.

Oxy-acetylene welding is also frequently used to weld cast iron. Also, it is an excellent option to minimize the extreme heating and cooling produced from the electric welding processes, and it is easier to maintain the temperatures of the components with it.

As brazing is not a welding process, but it’s a good option if there is trouble during welding; just make sure the surface to be brazed is cleaned well.

The next step involving is selecting the type of welding method. For each kind of welding, a brief description is given.

Using Stick welding for Cast Iron:

Stick welding also shielded metal arc welding consumable electrode covered with flux is used. Different types of the electrode can be used depending on the requirement.

Three main filler types that work well with cast iron

  • Cast iron covered electrodes.
  • Copper alloy electrodes
  • Nickel alloy electrodes

For cast iron welding nickel alloy electrode is the most common one as nickel-iron weld is stronger with a lower coefficient of thermal expansion, which will reduce welding stress and improves resistance to cracking also nickel electrodes can be used without a preheat.

Oxy-acetylene Welding for Cast Iron:

Electrodes are used in oxy-acetylene welding in this oxy-acetylene torch provides the energy for welding. Copper zinc electrodes and cast-iron electrodes are both suitable for oxy-acetylene welding of cast iron. In order to avoid oxidation in cast iron, care must be taken during acetylene welding, as this causes silicon loss and formation of white iron in the weld. Welding rod should be meted in the molten metal weld pool, rather than directly by flame, to minimize temperature gradient.

Braze welding of Cast Iron:

As in brazing, there is minimal impact on the base metal, so braze welding is a standard method for joining cast iron parts. This welding rod provides filler that adheres to the cast iron surface. Because of the lower melting point of filler compared to cast iron, the filler does not dilute with the cast iron but adheres to the surface.

For brazing, cleanliness of the surface is critical since the joint is dependent on the quality of the filler wetting the surface of the base metal. Fluxes are used in welding to clean the metal surface.

MIG Welding of Cast Iron:

Usually, MIG welding is not recommended as spatter produce from it can affect the base metal, but using desirable consumable in maintained condition welding through MIG can be possible.

Here are some tips for MIG welding of cast iron

  • For MIG, nickel wire is the best choice, but as it is expensive, so, stainless steel MIG wire can also be used.
  • 80/20 i.e., 80% argon, 20% carbon dioxide gas works excellent in most situations; the downside of this option is that the weld will rust eventually.
  • Brazing wire can also be used but is weak weld and not suggested for metals that experience impact or loading.

Use of TIG welding for Cast Iron:

For TIG welding nickel wire is the best option for this job. It is expensive, but the process can provide a clean weld on most cast iron jobs. For TIG, it is also possible to cold-weld i.e., skipping pre & post heating stages if correct gas, wire, and settings are used.

Also See: Best Welding Helmet for Tig 2020

Silicon Bronze for Cast Iron Welding:

I have seen many of my students and welding fellows to inquire about silicon bronze welding for cast iron. So I will keep this section straight. Remember, this method depends on the nature of the specimen.

  • Rinse the sample clean and preheat it.
  • Clean the welding part with a grinder to remove any disproportion of surfaces.
  • Now hold the sample and start with the small welding beads.
  • Make grooves and chamfer the surface with a torch and get deep penetration.
  • Now you can use Nickle rod with stick welding for welding.
  • There is also an option to use silicon bronze filler with Tig welding.
  • Let the specimen cool you are done.

A Quick Overview of the Whole Process:

info about welding

Welding of cast iron skillet:

For skillet welding, TIG welding with a Ni cast rod, which is 99% nickel rod or brazing can be used for cast iron. preheat temperature for brazing should be 9000 F and 13000 F for fusion welding.

If during welding didn’t want the coating on the inside of the skillet or the enamel on the outside, so for this preheat done below 5500 F and several steel metal plates heated up to 5500 F and skillet is then welded on the top of these hot metal plates. Both skillet and metal plates kept at 5500 F during the welding process with an oxy-acetylene torch with a rosebud tip.

Cast iron welding at home:

For the welding of cast iron to be done at home, it is crucial to follow some steps that are required to produce a welded part. Following steps should be taken before welding:

  • Identification of alloy
  • Cleaning the casting thoroughly
  • Selection of preheat temperature
  • Selection of appropriate welding technique

After the selection of alloy, whether it is gray (somehow weldable) or white (almost unweldable), cast iron cleaning of casting is done to remove any paint, grease, oil, and other foreign material from the weld zone. To remove the entrapped gas from the weld zone of the base material, it is useful to apply heat carefully.

As all cast irons are vulnerable to cracking under stress, so heat control is the vital factor to avoid cracking. Welding of cast iron requires three steps:

  • Preheating
  • Low-heat input
  • Slow cooling

Thermal expansion is the primary reason for heat control.  As the warm metal expands if localized heating is done this zone will be the expanded zone then the rest of the casting so stress will build up at this point and this localized heat zone will call heat-affected zone (HAZ)

Stress builds up in casting due to restricted expansion and contraction is relieved by stretching. Preheating decreases the thermal gradient between casting and HZ and minimize tensile stress caused by welding.

Check Also: Best Welding boots 2020

Some other Queries People Ask (FAQs):

Why does cast iron crack when it is welded?

The cooling rate is a key player here. If the temperature gradient from room temperature to the welding temperature would be sharp then it will generate thermal stresses which will result in cracking of the sample. So it is important that the sample should be preheated.

Do you prefer preheating cast iron before welding?

Yes, the reason is again the cooling rate. This process will let the cooling rate slow of the weld and the HAZ.

Conclusion:

Finally, we have ended this up. Cast Iron welding is a tough and hectic job. You have to go through a lot of processes to get this job done. Remember, whatever you are doing always take great care of yourself. Personal Protection is significant. You can see the best welding helmets 2020 guide; it covers a lot of detail regarding self-protection.

In the end, if you feel something is missing and miswritten here, you can always make your contributions in the comment section. Thank you!


Hello Everyone, I am James from Kentucky and been into this welding fiasco for 13 years in that time I have worked as a private welder and did most of the auto restoration work. In this recent, COVID-19 outbreak I decided to start a welding blog and share welding tips along with product reviews.

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