How to Weld Cast Iron

Welding cast iron has always been an issue among folks and I often hear lots of stories around people taking their cast iron parts to the local welding shop and being turned away all because some welders out there still believe cast iron cannot be welded, could this be true? Could this be a fact? Or is it all just down to the fact that those local welders do not have access to the right tools. For example, if all your mechanic has was a screwdriver, then it will be impossible to get any real work done.

The blank truth about the cast iron is that it can be welded, and a great number of welders out there have been doing this successfully for decades and maybe they are not just ready to share their secrets. Well, that ends today, as I would be taking you through all you need to know about welding cast iron and how exactly to weld cast iron. I am going to break it down so easily that In the end, you will realize you don’t need to be a pro to weld cast iron. Anyone with a complete box tool and a welding helmet should be able to make these repairs if instructions are followed critically.

Before we go into more details and in-depth discuss on how to weld cast iron, there are a few things I want you to have at the back of your mind while reading through this tutorial, first is the fact that welding cast iron is possible although based on experience among various welders, it is often put at a 50/50 chance of having a successful weld cast iron. However, note that, before any welding project, be sure to clean the casting, pre-heat the alloy, choose an appropriate welding technique, and Low and slow is the key to cast iron welding which means you don’t want to weld too much or get it too hot.

Cast Iron

Cast Iron is a hard, relatively brittle alloy of iron and carbon which can be readily cast in a mold and contains a higher proportion of carbon than steel. If you are starting out with welding cast iron, you should know that generally, it is more or less a 50% chance of success right off the bat. Cast iron usually has about 2 percent carbon in it, the rest of it is a combination of Iron and other trash elements and that is the reason why some of them weld great while some don’t produce a good weld at all. Most times just to make sure it has enough iron in it, you can decide to test it out with the use of a magnet to test the magnetic field around the material.

Cast Iron Carbon Problems

When welding cast iron, take your time to look at the break in the iron material you want to weld, you would notice that because cast iron has 2 to 4% carbon in it with a lot of silicon. The more carbon content your metals have, the harder and stronger they get, which makes them more crack sensitive. This is where welding cast iron comes in different, because while welding cast iron you need to start following the real rules of welding and not just striking an arc on a material.

Cast iron with lots of carbon content doesn’t have a lot of elongation in it, so what happens most times when you weld is that the weld shrinks, which in turn causes cracks mostly right down the middle of the weld.

This can be avoided or compensated through several ways and techniques, some of which are Pre-heating, braising, alloys such as Nirod, etc.

Normally, when welding Cast Iron, you want to preheat the part to a minimum of 3000F to prevent the cracking process during the cooling process.  Also, welding in small sections and skipping around will result in less distortion and relieve some of the stress around the weld which in turn reduces the chances of part cracking in the cast iron.

Deciding the Type of Cast Iron 

The initial step of this sort of welding is distinguishing what kind of cast iron it is. There are various sorts, and you won’t have any desire to weld the greater part of them. Here is a rundown of their weldability: 

Cast irons are a group of iron-carbon combinations. Their high carbon content (generally 2–4%) gives cast iron its trademark hardness. In any case, hardness comes to the detriment of malleability. It is less malleable in contrast with steel or wrought iron. The heating and cooling cycles during welding cause expansion and contraction in the metal, initiating pressure. Cast irons don’t extend or deform when heated, rather, they crack, making them very hard to weld. This trademark can be improved by including diverse alloys. 

Gray iron: Weldable with difficulty, they are the most well-known type of cast iron. Carbon accelerates out into graphite chips during assembling into either a pearlite or ferrite crystalline microstructure. It is more bendable and weldable than white cast iron. Be that as it may, it despite everything represents a test to forthcoming welders as the graphite chips inside gray cast iron can enter the weld pool to cause weld metal embrittlement. 

White iron: Almost unweldable, They hold the carbon as iron carbide without encouraging it out as graphite. The cementite crystalline microstructure is extremely hard and fragile. White cast iron is commonly viewed as unweldable.

Malleable iron: Weldable however uncommon, as it’s a broad and moderate procedure. 

Wrought iron: Not welded, as welding changes the properties of the metal, rendering it futile. 

The most ideal approach to determine what kind of cast iron needs welding is to counsel the item manually or contact the manufacturer if it’s not expressed on the material. There’s a slight distinction in the appearance of new cracks in the material, however except if you’re knowledgeable about deciding this, it pays to discover from the manufacturer. 

Gray cast iron is the most widely recognized sort of cast iron welded and ought to be the main cast iron you endeavor to fuse except if you’re knowledgeable about casting or welding it. Having somebody experienced to help you is another acceptable alternative.

Iron Casting Materials

Most of the time, there are several different ways to repair castings, and one of the ways is stick welding that makes separate different types of consumables, you can make a ferrule weld, a nickel 55 soft weld, and also a nickel 99 soft weld. The difference between them is that the ferrule weld is basically a steel electrode designed weld casting but it will not be machinable. So if you have to do any machine, you have to stare clear of ferrule weld. The nickel 55 has a lower end which gives it more strength and the nickel 99 which has almost a 100 percent nickel. This is because of it an absolute non-ferrous alloy that does not absorb any carbon in their weld so it is very good for single-pass welds or for castings that need to be machined. So make sure you are absolutely certain of the material you intend to use to weld your castings.

Pick the Welding Process to weld cast Iron

When you’ve decided the material is gray cast iron, the following stage is picking what process you will use to weld it. You can weld cast iron with each welding procedure if you utilize the correct filler material and welding technique. It’s basically founded on personal preferences, yet there are a couple of variables to consider. 

In case you’re welding up a machined surface, the best alternative would be to TIG weld it. The splash from MIG or stick welding may superfluously harm portions of the machined surface not being welded. TIG welding shouldn’t give you any scatter issues. 

Oxy-acetylene welding is another choice much of the time used to weld cast iron. It’s a decent choice to limit the outrageous warming and cooling of the electric welding procedures, and it’s simpler to keep up the temperatures of the parts with it. 

Brazing isn’t generally welding, as it doesn’t meld the metal as a weld does. Notwithstanding, it’s a decent choice in case you’re experiencing difficulty welding it for reasons unknown. Ensure the surfaces the brazing will adhere to are cleaned well, as it won’t adhere to messy or corroded iron. 

Stick and MIG welding are both attractive choices with the privilege consumables. With an inappropriate filler metal, it will undoubtedly cause splitting, so be certain you realize it’s the correct decision to weld cast iron.


Whatever alloy you opt for, if you intend to have more chances of success to cast welding, your castings must be well prepared before the welding process begins. These preparations involve careful cleaning of the casting in the area of the weld. This is usually done so as to get rid of all surface materials that may be present on the casting such as paint, grease, oil, and other foreign materials that might be stuck on the castings. Furthermore, professional and experienced welders advise that you should apply heat as carefully and slowly as possible to the area of the casting you intend to weld so as to remove all entrapped gas from the weld area of the base metal.    

So how about we discuss a simple technique often used to determine the readiness of your cast iron. This technique simply involves depositing a weld pass on the metal, if it turns out to be porous, that would indicate that there are impurities present, at this point, you would have to do some grinding off and repeat the process until the porosity disappears.


When faced with casting, you need to take look at the cracks to see how much of a crack it is and if it’s a full crack all the way through the casting. If the crack is not all the way through the casting, you would have to take a grinder carbide drill or anything of that nature that could take on and remove the material then you should V it out into around a 30-degree bevel and you might want to remove all of the cracks. Once that is done, the next step is to clean the material and then add a preheat to the casting.

The basis of preheating in the casting is to prevent the casting from cooling very fast. Preheating limits cracking problem or hopefully stops cracking problems totally. If you decide to just weld on an iron casting without any preheating, it will cool too fast and you would hear an awkward sound which only means your iron castings are just cracking again. Whatever you do you have to control the preheating in the casting. Welders who are really into iron cast weld make use of a small tool called the Temple stick which is marked with both Celsius and Fahrenheit, and there are also various degrees that they melt at. Suggested preheating is between 5000 to 12000 Fahrenheit

After preheating, you should touch the temple stick to the casting, and if the temple stick melts, that would mean you can weld on the casting. Meaning iron castings has enough heat into it to keep it from cracking. Also, if you intend to limit yourself in a perimeter of thermal, you can take a 3000 or 5000 level temple stick or even as high as a 7000 or 9000 temple stick. Then you can decide to stay within these ranges of heat temperature degrees to keep the casting in place, ensuring it’s not getting a lot of stress.


As discussed earlier, cracking is somewhat a common problem in welding iron cast, and it occurs during the welding stage which is termed the thermal contraction phase. When these contractions build up beyond the yielding point of the cast iron material, the weld cracks.

One method welders often use to reduce these encounters of iron cast cracking is a technique called peening which involves moderately striking the weld with a ball-peen hammer to a deformable weld bead while the weld is still soft. This technique and process decreases the risk of cracking in the weld quite significantly but a quick warning is this technique should only be used when working with a relatively ductile weld metal

Slow Cooling

After the casting, you can easily take a slow cool either by wrapping the iron casting in a fireproof blanket or put the casting in a helmet and drop it to a bit down 50 degrees an hour. This will allow the casting to acclimatize steadily to the cooling process allowing it to stress relief itself. But I’m sure as a home welder you are wondering if you have all these cooling methods at home. well, there are simpler and more accessible ways which include burying in the sand if you have to, the main aim here is to control the slow cooling of the casting.

Secret Method To Iron Casting Cooling When you are at Home

I’ll let you in on a secret of what I do for the controlled cooling of iron castings which works pretty fine for me and other welders I know. I take charcoal and put it in a grill and let it burn out while I am working on the casting itself, and after the charcoal is burned out, I’ll throw in more charcoal. When I am with the iron cast weld, let’s say for about 2 hours, I throw the iron casting in the charcoal grill and let it come down for about 2 days. This is one method you cause when trying to repair things at home.


Welding cast Iron might seem difficult but it is not impossible if you follow the right procedures carefully, as I mentioned earlier Iron cast welding is more than just striking an arc on the material it follows specific welding rules and procedures.

When an in-house iron cast welding is done effectively, it saves you a lot of time and money and although the honest truth is that it can be quite difficult to successfully perform an iron cast weld, it comes with a lot of welding failures resulting from cracks and other damages that come with it. If critical parts are involved, it may be wise to seek the workmanship of a welding facility with experienced welders to ensure a successful result.

If welding is performed in-house, it is crucial to research the steps required to effectively produce a welded part. Four key steps should be taken before getting started

From our guidelines o how to weld cast iron, you should be able to get with iron cast welding yourself or at least have enough insights to try. If not you can always contact a welding pro around you for more practical. Good Luck Welding your next cast Iron!   

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