If you are looking to weld cast iron, this guide will give you an idea of what to expect as you go about doing it. To break a cast iron item, part or structure is a huge inconvenience, but if you can weld the item yourself, it is lots of money and headache saved. Let’s begin learning how.
Figure Out Your Cast Iron
Firstly, you have to figure out what kind of cast iron you will be working with. Most of them you may not be able to weld. Here is a quick list:
- Gray Iron - Can be welded, quite difficult
- White Iron - Nearly impossible to weld
- Ductile iron - Can be welded, rarely done as it is slow and time-consuming
- Malleable Iron - Cannot be welded.
Machining The Part?
If you are machining the part after you complete the weld job, use a nickel type electrode.
Determine Your Welding Process
If you will be welding an object that was machined, TIG welding would be the way to go. Thanks to the splatter of MIG and Stick welding, the machined object could end up damaged unnecessarily. Thankfully, TIG welding will keep things clean.
Other options you can use is oxy-acetylene welding, which is commonly used in the welding of cast iron. It helps keep the extreme heat and and cool-down of welding methods to a minimum, and is simpler to keep track of the temps of your components with this method.
Brazing is also a fine choice in the event you are having a difficult time welding.
Lastly, so long as you have the right materials, stick or MIG are fine to use-otherwise, cracking could be an issue. Make sure you have all the right welding machines and materials in place before you use these methods.
Pick Out Filler Wire and Electrode
Only a select few filler wires and electrodes will weld cast iron correctly. Choose the right ones because if you go with one not designed for cast iron, it will cool too fast and leave you with stress cracks. Or, it may not fuse with cast iron properly.
Good Filler Wire and Electrode Choices
- Iron - This is cost effective and creates a different colored weld than cast iron. This is tough to use thanks to the higher shrink properties. It should be noted that this material is NOT machinable, thanks to how it hardens during the welding process.
- Nickel/ Iron Mix - Consisting of 55% nickel and 45% iron, this type of welding rod is affordable and looks like cast iron once totally welded. This weld is machinable and has reduced shrink in from welding than other iron rods, which means cracking is minimized.
- Rich Nickel - This is the ideal type of electrode or wire to use thanks to its soft, machinable properties. It looks just like cast iron and does not cool down too fast. The disadvantage is that these consumables are quite expensive and are not ideal for welding thick sections.
- Brazing bronze - Welders can use rods and a TIG welder or oxy-acetylene braze. This is great for providing a durable bond in a crack or among 2 parts that need to be joined. It’s great because it does not cause cracking nor change of the cast iron properties.
- Stainless Steel - Cast iron fused with austenite stainless steel will not harden and alter the properties of iron consumables. The stainless steel will expand and contract a lot during the heating and cooling process of welding, making it a challenge to use. Despite this, it is still great for making a machinable surface and for welding cast iron.
Clean Off The Casting
Make sure you begin by cleaning off the casting properly before you begin welding. Clean off any materials from the alloy’s surface, such as paint or grease, dirt, and other foreign materials. Make sure that when you apply heat to the weld area you do it slowly and with utmost care. This helps get rid of any gas trapped in the weld zone.
Should I Cold Weld or Pre-Heat?
More often than not, pre-heating is the way to go. However, some applications are okay for cold welding.
Cast iron’s quite brittle and is not able to deform as well as some other metals when bending or expanding and contracting. Heat makes metal deform, and if one piece cools or heats faster than the other, you can be sure that cracking will occur either in the metal or the weld.
Preheating is the way to go because it brings the area of your weld closer to the temp at which you will be welding, helping the whole part to change in a uniform way. The characteristics of cast iron change once the temp reaches 1400 degrees F, so excessive heat isn’t critical.
On the other hand, welding cast iron using cold methods may help in not creating visible cracks. It will create a more durable weld than a hotter weld minus the need for preheating. It should be noted that stress internally still happens, which shows up later on for the component being welded. It creates a weaker weld overall compared to correctly preheating before the weld takes place.
That being said, preheating is the way to go. This way you can be sure it is strong inside and out.
Cool It Slow
Don’t use compressed air or water to cool the weld. Allow it to cool off over a few days if needed. If using gray cast iron, you might be able to put it in the sand or warm oven. It’s best to just take it slow- you will get a better overall result.
It’s not going to be easy to weld cast iron, as it requires a lot of prep and patience especially when it comes to the cooling process. It’s best to just take things slow and do it right the first time, as not doing so could leave you with cracks or just a weak overall weld. Take your time and do it right-you will be glad you did.