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Welding Cast Iron

Thursday, 19th March 2020
Graham (Tech Advisor)
The Welders Warehouse Online Shop

Welding Cast Iron has quite a few potential pitfalls, but if done correctly, it’s not difficult.

Why is Welding Cast Iron problematic

The key reason why welding cast iron can be problematic is the high carbon content.  During the welding process, this carbon migrates into the weld metal and/or the heat affected zone adjacent to the weld metal, causing elevated hardness/brittleness.  This is how Cast Iron gets its reputation for post weld cracking.

Process for Welding Cast Iron

Gas Welding heats the Cast Iron slower than Arc based processes and the flame is lower temperature than an arc.  This means Carbon migration is not normally a problem.  Use of a proprietary Cast iron Gas Welding rod is important.  The only real downsides to Gas Welding Cast Iron is the amount of heat needed if components are large.  Gas Welding is also a slow process.

Arc/Stick Welding is, arguably, the best all-round process for Welding Cast Iron, provided the correct welding rods are used.  Cast iron Welding Rods have a special Graphite rich flux, this graphite chemically ties up the Carbon in the Cast Iron, limiting migration into the weld metal and heat affected zone.  There are two common types of Cast iron Welding Rod, Ferro-Nickel and Pure Nickel.  Ferro-Nickel are typically 53% Steel and 47% Nickel.  Ferro-Nickel Rods are cheaper than pure Nickel and are ideal for welding Cast Iron to Steel.  Pure Nickel will produce a softer, more malleable weld deposit.  I would advocate using Ferro-Nickel, unless the job specifically requires Pure Nickel.

Mig Welding is, in my opinion, not a great way to weld Cast Iron.  Whilst there are specialist Flux Cored Wires available, unless you have a repeating application that you can create a procedure for, I would not advocate Mig Welding Cast iron.

Tig Welding is not considered a suitable process for Welding Cast Iron.  An open arc process such as Tig offers no opportunity to mitigate Carbon migration.

Welding Techniques

Gas Welding – There are no specific techniques that need to be deployed.

Arc/Stick Welding – All of the following are important:

  1. Prep the job with a ‘U’ shaped groove, avoid sharp corners as this can lead to heat build up which will exacerbate carbon migration.
  2. Use the correct type of welding rod.
  3. Ensure the component is AT LEAST at room temperature, adding a small amount of pre-heat will help, but you only need the component to be warm to the touch.
  4. Limit the amount of welding done in one run.  As a rule of thumb, do not put down a continuous run that has a length greater than 10x the diameter of the welding rod being used.  Having said that, it’s ok to put down multiple runs in different parts of the component (see graphic in next item).  Eg, if repairing a 300mm crack with a 3.2mm rod, you can weld a run of 32mm, then do another 32mm run in another part of the crack.  Avoid letting the weld area get too hot, this is the purpose of short runs.
  5. If you’re repairing  crack, run a bead across each end of the crack to avoid the crack spreading further.
  6. Keep the welding rod vertical, not at an angle, like you would for most stick welding.
  7. Don’t expect to weld cast iron quickly, the key is to take you time and do it properly.

I hope you found this blog article about Welding Cast Iron useful, if things work out well for you, please feel free to post some pictures of your achievements on our Facebook Page

Please let me know what you thought of this article by leaving a comment.  Don’t worry, your email address won’t be added to a database or shared and you won’t receive any unsolicited email.





  1. Anold says:

    I want to welding my three leg pot please help me with the process

    1. Graham says:

      Hi Arnold
      The information in my Article on welding cast iron should be sufficient to help you with the job:
      Otherwise, take the job to someone with experience of this kind of repair on a cast iron item.
      Regards Graham

  2. Jan Alsemgeest says:

    Hi Graham. Thank for sharing your knowledge.
    I want to weld-up the cast iron combustion chambers in a 60ties V8 cilinderhead for the reason to reduce the volume,re-shape and make it more efficient (read more HP). I’m planned to heat the head to 600 till 800 degrees Celcius and then arc weld it with rods.
    Do you have advice what rods to use, what Amp to use and how to temper the head after welding (the time needed to cool of to room temperature?). Other adices are welcome. For our race class we are stuck to these heads and therefor I start this project. Thanks in advance.
    Best regards Jan from the Netherlandse

    1. Graham says:

      Hi Jan
      Pre Heat sounds good, although 300ºC should be adequate.
      Ensure you heat the Cylinder Head evenly to avoid the risk of distortion.
      I would use a Ferro Nickel type rod.
      The size of rod will depend on how big the parts are and how big you want the weld to be. I would guess 2.5mm or 3.2mm diameter rods, given a V8 Head is likely to be quite big, but I don’t know how much weld you need to reduce the volume.
      Cool the Cylinder Head as slowly as possible, maybe put it in sand, or surround it with bricks. The slower it cools the better.
      I regret I don’t have experience of tempering a Cylinder Head, so you will need to seek advice elsewhere for that.
      Hope that helps 😀

  3. Walt Bolthouse says:

    I would really appreciate any advice you could give me regarding stick welding or brazing 10 ft lengths of 6″ ID Cast Iron water pipe together to make 20 ft lengths and then 1008 steel flanges ½” thick at each end to connect these together. This is CISPI 301 sewer pipe, I believe to be grey iron which would have minimum C content of 4.1% by spec. Wall thickness of the tube is roughly ½”

    1. Graham says:

      Hi Walt
      I regret I can’t really add anything to the information contained within the blog article regarding technique and notes on welding Cast Iron. It’s not possible for me to write you a specific weld procedure without being a lot more involved in the job and I can’t get that involved.
      You might be best off speaking to someone local to yourself who has experience of welding cast iron, as they would be able to get more involved.
      Sorry I couldn’t help any further.
      Regards Graham

  4. Bernabe Mercado says:

    Very good tutorial,good explanation on welding.

    1. Graham says:

      Hi Bernabe
      Thanks for the comment, glad you found the article on Welding Cast Iron useful.
      Regards Graham

  5. Rene Exner says:

    Hi Graham
    Thank you very much for your advice It was a great help.
    It look like the bit I need to weld is a steel casting.
    Many thanks

  6. Rene Exner says:

    Hi Graham thank you very much for your reply.
    This a part that has been cast and put onto the bike frame it has two lugs one of witch has snapped though the center of the bolt hole witch would mount the main stand of the BSA D7 Bantam.so I am thinking grinding away the existing threads putting down a weld as you said with a cars iron rod then building the rest up with a standard metal rod would this be ok? Many thanks

    1. Graham says:

      You’re welcome, glad you’ve managed to get the job sorted!

  7. Rene Exner says:

    Hi Graham
    I Have a BSA bike frame that has a cast iron bit that has broken that holds the main stand what welding rod should I use to build it up as I don’t have the piece that brock off?
    Kind regards

    1. Graham says:

      Hi Rene
      If you’re welding onto Cast Iron you will need to use a Cast Iron Rod.
      Having Said that, once you have a layer of Cast Iron welding rod on the Cast Iron, you could use a different material to build up. So the Cast Iron rod would act as a buffer between the Cast Iron and a different material on top. I say this because Cast Iron welding rod deposit is pretty soft and so might not be ideal. I can’t be specific because I’m not familiar with exactly what you need to do or how much wear or stress the finished weld will be under.
      hope that helps, at least a bit 🙂
      Regards Graham

  8. Randy Bryant says:

    Have a crack in a tractor motor block, oil seeps from it, how well does the Mickle rod work with contaminated cast?

    1. Graham says:

      Hi Randy
      Welding contaminated cast iron is not a good idea! You will need to eradicate the contamination before you attempt to weld it. Try heating it up gently with a flame to burn off the oil contamination.
      Hope that helps, Graham

  9. Dan Green says:

    Any suggestions on vertical and overhead cast iron weld

    1. Graham says:

      Hi Dan
      Technique would be much the same as welding steel in position, just take care not to weld too much in one go. Lots of short bursts!
      Hope that helps!
      Cheers Graham

  10. Joseph says:

    Hi Gram its Joseph here tomorrow or its already I am going to weld Isuzu block cast iron I have your tips I will be be using mig but it consists of arc, co2 ,aluminum let you know when finish

  11. Carol Davis says:

    I have a gas stove, over the burners is cast iron that the pots and pans sit on, the [weld’s?] are coming apart so they don’t sit level nor can they be slid from one side to the other as I have 2 sides/parts to the top. I’m wondering if JB weld would hold up during cooking. I could just twist wire together tightly and just be satisfied as they’re pretty expensive to replace and I can’t spend a lot of money on the and from what I’ve read welding might ruin them so I HAVE to replace them and I can use them as they are but I’m thinking that they might just get worse with more coming loose…..I totally understand if you can’t help but you don’t know if you don’t ask. Thanks in advance for your time. Carol

    1. Graham says:

      Hi Carol
      Hard to comment in any depth without seeing the issue/job.
      My first thought is that if the issue is likely to get worse, to the point when you have to replace the parts, you have little to lose from trying a repair!
      If you decide to try a repair, the first thing to do is establish the metal is definitely Cast Iron.
      Easiest way is to grind a small area and see what colour sparks are produced. Red sparks mean Cast Iron, Orange sparks mean Steel. It’s then a case of using the correct Welding Rod.
      If it’s Cast Iron, then use a Cast Iron rod (Obviously 🙂
      If it’s steel, I would suggest our 312 dissimilar rods as they are very strong, and crack resistant.
      You can find both on our Welding Rods Page.
      I hope that helps.
      Kind Regards Graham

  12. Brad says:

    I recently bought a 1950’s radial drill press. One of the cast molded corners a a trough is chipped about 1/2″ x 3″
    I have arc welded exhaust manifold with ferrous nickle rod.
    To keep the trough shape I’m thinking of molding a pumice stone to the shape of the trough. Then slowly do a build up.
    Do you know of any problems with pumice.
    Do I need to heat the cast with a torch first?
    I’m painting when done non structural.
    I will grind outside to shape when cool

    1. Graham says:

      Hi Brad
      Not aware of any issues with Pumice, but don’t really know either way I’m afraid.
      Some pre heating is wise with old castings, hand hot should be sufficient.
      Remember to lay down short runs only, length 10 times rod diameter is ideal.
      Good Luck

  13. Tony says:

    Hi we need to weld s355 plate to graphite cast what rods do you suggest

    1. Graham says:

      Hi Tony
      I would suggest a Ferro-Nickel Cast Iron Rod.
      You need the Graphite type flux that these rods have.
      2.5mm Ferro-Nickel Rods
      3.2mm Ferro Nickel Rods
      Most of the technique points made in the blog article will still apply as it’s the Cast Iron that can cause problems.
      Hope that helps
      Cheers Graham

  14. Dave says:

    Hi Graham I have a large cast steel component to weld I believe it’s cast steel and the damage is on the side faces of bush housings if you can imagine 4 220 mm housings interlocking with a machine with the same configuration and connected horizontally by a 120 mm pin through bushes in the component , question is where bushes have broken up between faces it has chewed up the steel so I need to build up with wire or rods and face back up or maybe grind flat again what would you recommend nickel ?

    1. Graham says:

      Hi Dave
      Easiest way to check if a component is Steel or Cast Iron is to grind a small piece of it. If you get a stream of Orange sparks, it’s most likely steel. If you get a short stream of Reddish sparks, it’s most likely Cast Iron.
      If it’s Cast Iron I would use a Ferro Nickel Cast Iron MMA Rod
      If it’s cast steel then I would really need to see the job, but based on what you’ve said, Chrome Nickel Rod like our Dissimilar Steels rod would be a good bet.
      Hope that helps.
      Cheers Graham

  15. Paul says:

    Need some advice on welding cast housing on a Transmission but it’s all vertical job wondering if its possible? Also how weak it will be compared to prior brake?

    1. Graham says:

      Hi Paul
      Welding Cast Iron vertically is possible, but would be a challenge, better would be to remove the transmission and weld it flat. Strength should be OK, if all is done correctly. Cast Iron is unforgiving if you try to take short cuts.
      Hope that helps
      Cheers Graham

  16. justine kotati says:

    very educative article have really learnt slot

    1. Graham says:

      Thanks for the comment Justine, glad to hear you found the article useful.
      Kind Regards

  17. Jim Barnett G0JGB says:

    is the new cmt technique suitable for cast iron ?

    1. Graham says:

      Hi Jim
      I regret I’m not familiar enough with the Cold Metal Transfer process to definitively answer your question. I’m inclined to think it would not be suitable, because of it’s use of an open arc, but my suggestion would be to speak to a specialist like Fronius for a conclusive answer.
      Sorry I couldn’t be of more help
      Kind Regards

  18. marc Wheatley says:

    I am looking for supplies for arc welding cast. I live in Derbyshire. Dose BOC sale them.

    1. Graham says:

      Hi Marc
      Sorry I haven’t been able to reply sooner. I can’t speak for BOC, but you can find our Cast Iron Rods on this page:
      Cast Iron Rods
      Cheers Graham

  19. Steve says:

    What are the chances of being able to mig braze an engine block, mane the pros and cons

    1. Graham says:

      Hi Steve
      You would need to get the whole engine block hot to have a sporting chance. Using Mig on Cast Iron is risky because arcing on Cast Iron can cause the formation of White Iron, which is incredibly hard and brittle. If you are going to try it, place a piece of steel on the block and arc up on that, then run off onto the block. You will need to cut the piece of steel off afterwards.
      Personally, I would Braze it with an Oxy/Fuel Torch, or Stick Weld it.
      Hope that helps, good luck.

  20. davidokeefe says:

    Years ago gas welded some thick cast iron plates pre heated plates can’t remember temp but was quite high pre heat.after repair was finished I placed Weldmet in a box with a fine sand covering it fully and this helped to cool slowly but I would think filler materials have advanced a lot now great column graham

    1. Graham says:

      Thanks for the comment David
      Filler materials have advanced, but your method is still sound, especially where repairing older cast iron parts that may not be made from the best quality material. 300⁰C is a good pre-heat temp, but as you clearly know, any pre-heat helps as it reduces thermal shock.

  21. Wilfred Moses says:

    That’s really an informative article.
    However one more thing to add is that the welder’s hand should be steady and should be kept with a constant speed throughout the weld.

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