Last Updated on September 2020
Cast iron, as you must be aware, is among the most challenging and often difficult metals to weld. You not only need a precision TIG welder but also experience on how to subject the cast to high amounts of electric power.
Cast iron can be deceiving to the eye. That is, it might appear strong after welding despite being weak internally, which can lead to cracks eventually. This means that you need to be well informed on how to weld cast iron to avoid wasting time or spending unnecessary cash by bringing in more experienced welders to perform tasks that you can do yourself.
We understand that welding cast iron is no walk in the park, which is why we have compiled this ‘how to’ guide to help you out.
Provided you follow the instructions we list and explain below, we guarantee you that welding cast iron will never be the same again. It might not become any easier, but the additional information will surely help you to avoid making silly mistakes and even better, know the tricks as well as the ins and outs of proper cast iron welding.
Steps On How to Weld Cast Iron Effectively
Step 1: Determining what type of Cast Iron you are Working On
There are different types of cast iron such as the common gray iron which can be welded, albeit with some difficulty. Other types include white iron (almost impossible to weld), ductile iron (difficult, slow and demanding to weld) and malleable iron (iron that cannot be weld as doing so alters the metal`s properties).
You can always understand the welding properties of your material by checking the manual or contacting the manufacturers. Of course, for experienced welders, it is always easy to observe the cracks and determine the repair routine.
The most popular type of weldable iron is gray cast iron. Although it might be challenging to weld this material, it is something you can manage with a proper welder.
The Cooling Factor in Cast Iron
Cooling is an important part of any welding project. When the castings are being prepared, the molten iron is usually carefully poured into a hot mold and left to cool slowly. Here`s an important point to keep in mind, cast iron usually has 2-4% carbon content, which is almost ten times more than other steel products. The high carbon concentration leads to the formation of graphite flakes, which gives the cast iron the grey color when it is fractured.
All castings should be allowed to cool gradually or should be kept cold enough such that the cooling rate becomes a non-factor.
Step 2: Determine the Appropriate Welding Process
Cast iron can be weld using almost all welding processes as long as you utilize the right filler materials and observe the processes to the latter. It all depends on your preferences in addition to several other factors such as these:
Surface being Weld
TIG welding is always the best method if you are welding a specific part of a machine. When fixing or repairing a small portion of an item, you have to be careful as spatter emanating from welding the surface under repair can ruin the appearance of the entire item. TIG welding doesn’t leave loads of spatter like stick welding or MIG, thus reducing the risk of spatter ruining the appearance of the entire surface.
Durability of Welds
MIG and stick welding can give you the best and most durable welds. Their use, however, comes with a caveat; you must use the right consumables. Utilizing incorrect filler metal will almost certainly lead to cracking, no matter the quality of welder you use. Therefore, be sure to check for compatibility before MIG or stick welding a particular surface.
Cooling and Heating Factors
Another point to consider is whether you are comfortable with the extreme cooling and heating temperatures associated with electric welding. Oxy-acetylene makes it easier to maintain temperatures and perform your welding tasks. You can also choose to braze (really isn’t welding) if welding the surface is proving a bit too difficult. Ensure the brazing surfaces are well cleaned as brazes rarely stick on rusty or dirty iron.
Step 3: Select the Electrode or Filler Wire
As mentioned in step 2, you have to be extra careful of the materials you use when welding. Some options will not fuse appropriately with cast iron, leaving an unappealing appearance while others tend to cool to quickly thus leading to stress cracks. Below are some of the options you have when it comes to wire consumables and electrodes.
Electrodes Rich in Nickel
These wires are often soft and highly machinable. Nickel is known to cool gradually, a feature which is ideal as it will cool at approximately the same pace as cast iron. Even better, nickel rich material is known to have the same gray appearance after cooling. These electrodes aren’t ideal for welding thick areas and will cost quite some dollars to acquire.
Nickel (55%) and Iron (45%) Alloy
Although these alloys are harder than electrodes that have high nickel content, they are still machinable and cool off to the same color as the cast iron, leaving your weld looking neat. These alloys are great for use due to affordability and low-shrinkage rate, meaning it doesn’t crack as much as iron.
Iron doesn’t cool to the same color as cast iron during welding. Expect a tougher challenge when using this material as it has high shrinkage properties and is not machinable. You can however, ground back iron when welding.
Stainless steel is not known to expand or contract often when exposed to heating and cooling during welding. This makes it difficult to weld cast iron. But, using it to weld cast iron will help you produce a machinable surface.
Step 4: Preheating or Cold-Welding
Before beginning your welding process, it is crucial to first clean up the surface. For top-class, durable welds, we recommend welding on clean surfaces free from rust, grease, dust or any other type of contamination. This will ensure that your weld comes out neat and durable.
Preheating is always advisable to take advantage or cast iron`s brittle properties. Since heat is known to deform metal and their internal properties, preheating helps spread out the heat evenly to prevent uneven cooling that normally leads to cracks.
Preheating allows you to make the weld`s surrounding areas share similar welding temperature, thus allowing the entire component to change in uniform fashion. But, since cast iron has a limit of 1400 Fahrenheit, it is recommended to avoid exceeding that level to prevent deformation.
You can also choose to cold-weld, although you should be well-experienced to try out this technique. Cold welding doesn’t involve preheating and utilizes a minimum amount of heat to change the properties of materials.
When cold welding, it is advisable to raise the casting to a temperature of 100 Fahrenheit.In cold welding never overheat to an extent you can`t touch the cast with your bare hands. With this technique, make short welds that measure approximately 1″. Always peen after completing your weld when cold welding. Remember to also fill all craters and deposit beads in a uniform direction for good outcomes.
Although this technique might be ideal for some, it is not as preferred as preheating since it can lead to weaker welds due to internal stress.
Step 5: Cool Slowly
You can`t have a successful weld project without allowing the weld to cool without any interference. Introducing compressed air or cold water is a sure recipe for internal cracks. You should allow the entire component to cool of slowly, and naturally. Remember to always allow the component to take as much time as possible to cool. Consider placing the welded item into a warm oven or sand to ensure it cools uniformly.
Unfortunately, most inexperienced welders tend to focus more on the physical processes of welding, leaving out the extra-crucial area that is proper cooling. You have to provide the right conditions for your welded component to cool off. As we stated earlier, uneven cooling leads to internal cracks and affects the durability of the weld in the long run.
As we have established from our above discussion, welding cast iron is not easy but it is possible. While the chances of success are often slim for first timers, you don’t have to make weak welds to learn how to weld cast iron.
All the tips and steps provided are guaranteed to help you understand the cast iron welding process better. Ensure that you first understand the type of cast being weld. Afterwards, determine the best welding technique to use. Be sure to keep factors such as spatter and section being repaired in mind when deciding the best welding methods.
Another important tip to always consider is welding on clean, uncontaminated surfaces. Welding on such surfaces will produce weak welds that can`t last long enough to fulfill their purpose. Rushing the cooling process will not only lead to cracks, but it will also lead to the formation of weak internal links in the iron.
Having shared the basics about welding cast iron effectively, we are confident that you can take to the garage and get one brilliant weld done. It`s not easy- we know, but you are now better placed to come up with a strong, aesthetically appealing cast iron weld.