In this article, we will learn the overview of cast iron, basic details, meaning, whether you can weld cast iron or not, Is Cast Iron Malleable and Weldable or not, etc. Let’s explore!
What Do You Mean by Cast Iron Welding?
The cast irons are a family of iron-carbon alloys that are used in construction. The basic constituents of cast iron consist of iron and carbon in varying proportions, as well as additional elements such as silicon, manganese, chromium, nickel, copper, molybdenum, and more, that help improves certain properties.
Furthermore, it is sulfur and phosphorus levels can be significantly higher than their impurity levels, making welding difficult without cracking due to the high sulfur and phosphorus levels.
- A wide variety of cast iron types can be found in the market today, such as grey cast iron, white cast iron, ductile (nodular) iron, and malleable cast iron, all of which can be worked in varying ways. Cast iron is considered weldable in all categories except white iron, although welding cast iron can be significantly more challenging than welding steel due to the nature of the material.
- There are some cast irons that are malleable, but most cast iron is brittle. In the automotive industry, cast iron is used for parts such as cylinder heads, cylinder blocks, and gearbox cases because it has a relatively low melting point, is fluid, cast able, has excellent machinability, is resistant to deformation, and is wear resistant.
- Cast iron has become an engineering material with a wide range of applications and is used in pipes, machines, and parts of the automotive industry, from pipes to machine parts. In spite of its resistance to oxidation, it is very difficult to weld due to its notoriously tough nature.
Is Cast Iron Malleable and Weldable?
It is possible to weld cast iron, but it is problematic because of the high carbon content of the metal. Most steels in this category have a carbon content of about 2% to 4%, which is about ten times greater than that of most steels.
- A significant amount of carbon is migrated into the weld metal during the welding process as well as into the heat-affected zone, which in turn leads to an increase in brittleness and hardness of the metal. This, in turn, can lead to cracks appearing after the welding process has been completed.
- The majority of cast iron types, apart from white iron, are considered to be weldable; however, when compared to welding with carbon steel, welding cast iron can pose a significant challenge. Although it is possible to tell the difference between these two types of cast iron without detailed metallurgical analyses, it can be quite difficult to tell the difference between them. However, cast iron has been used for centuries despite the fact that it is a durable, wear-resistant metal.
Can You Weld on Cast Iron? Is it Complex to Weld?
Cast iron might be challenging to weld due to its unique composition, as was already discussed, but it is not impossible if you apply the right welding procedure to prevent weld fractures. This need for careful heating and cooling, frequently involves pre-heating, using the right welding rods, and letting the item cool gradually.
Without a thorough metallurgical investigation, it might be challenging to differentiate between these many cast iron varieties. Nevertheless, cast iron has been around for a very long time and is a durable metal.
What to Do Before Pre-Welding Casted Iron?
In order to ensure that cast iron is effectively welded, there are four main steps that need to be taken before getting started. Among them are the following:
- Identifying the type of cast iron and alloy
- Cleaning of the cast
- Choosing the Right Pre-Heat Temperature
- Selecting the proper welding technique
Identifying the type of cast iron and alloy
To begin with, it is necessary to identify what type of cast iron is being welded. Once this is done, the welding process can begin. A number of different types of welding are available, but you will not be able to weld the majority of them.
Cast iron is not a ductile material, so when it is rapidly heated or cooled, it can crack from thermal stresses due to its poor ductility. Depending on the type and category of cast iron, the susceptibility to cracking will vary.
To be able to determine which type of alloy you are working with, you must first know what type of alloy it is. The types of alloy are as follows:
Grey cast iron
In terms of cast iron, this is the form in which it is most commonly found. During the manufacturing process, carbon precipitates out into graphite flakes, which then form either a pearlite crystal structure or a ferrite crystal structure. As compared to white cast iron, it is more ductile and wieldable. Regardless, gray cast iron still poses a challenge to prospective welders because the graphite flakes contained within it may enter the weld pool and cause the metal to become embrittled when welded.
Compared to steel, grey cast iron has a lower tensile strength and shock resistance, but it has a similar compressive strength to low- and mid-carbon steels. Graphite flakes are sized and shaped in such a way that their mechanical properties control the mechanical properties of the microstructure, which can be characterized following the guidelines provided by the AST based on their size and shape
Ductile and nodular iron
In terms of composition, ductile iron is similar to grey iron, but it has a much lower level of impurities when compared to grey iron. There is a difference between grey iron and ductile iron in that grey iron contains carbon in the form of flakes of graphite in the matrix, while ductile iron contains graphite in the form of spheroids
. Other than the graphite spheroids, there is primarily pearlite in the matrix with a region of ferrite surrounding the graphite spheroids.
Malleable Iron
Malleable iron is made from white iron that has been heated and treated in such a way that the carbon content is substantially lower than that of white iron. There is typically a mixture of ferrite or pearlite structure with nodules of graphite added to the iron, depending on the type of heat treatment employed. Thus, it has a higher degree of ductility than standard white iron due to its mixture of ferrite and pearlite.
Checking the specifications of the iron you are working with is a simple method of determining which type of iron you are working with. The analysis of the chemical and metallographic characteristics of the cast iron can also help in identifying the type of alloy in the cast iron with which you are dealing.
There are also some techniques for telling the difference between the alloys, such as when the grey iron shows grey along a fracture, while white iron will show a whiter color along the fracture due to the cementite it contains. As well as showing a whiter fracture, ductile iron, for instance, has much better weldability, even though it also shows a whiter fracture.
Cleaning of the cast
No matter what the alloy is that is being used, it is important to properly prepare the casting before welding is performed. Before welding the casting, one of the most important things you should do is to remove all materials that are on the surface of the casting before welding the casting together.
Welds must be made on castings that are completely clean around the areas where they are going to be welded. Ensure that the weld zone is free from paint, grease, oil, and other foreign materials. In order to remove entrapped gas from the area of the weld in the base metal, it is best to apply heat to the weld area for a short period of time in order to apply heat carefully and slowly.
In order to determine if the surface of the cast iron is ready for welding, a simple technique is to deposit a weld pass over the surface; if there are any impurities present, the weld pass will appear porous. It is possible to grind off this pass, and this process can be repeated a few times so that the porosity disappears completely.
Choosing the Right Pre-Heat Temperature
When cast iron is subjected to stress, it is susceptible to cracking. In order to prevent cracks, one of the most important factors that need to be controlled is the heat.
To make a cast iron we require the following steps:
- Pre-heating
- Low heat input
- Slow cooking
It is primarily due to thermal expansion that heat is controlled. As metal warms up, it expands, so when it is heated, it expands. An entire object will not build up stress when it warms and expands at the same rate, but it will build up stress if heat is localized to a small heat-affected zone (HZ) within the object.
- There is a tendency for localized heating to cause restricted expansion of the HZ since the cooler metal surrounding it limits its expansion. There is a direct relationship between the degree of stress caused by the HZ and the casting body in terms of the thermal gradient. Stretching is one of the ways in which steel and other ductile metals are able to relieve the stress that is built by restricted expansion and contraction.
- The cast iron material has relatively low ductility, so this can cause cracking during the contraction period as a result of the contraction. In order to minimize the tensile stress caused by welding, the pre-heating of the casting body reduces the thermal gradient between the casting body and the heat zone. It is generally accepted that higher temperature welding methods require a higher pre-heat temperature in order to be successful.
- It is best to use a low melting point welding rod or wire or a low-temperature welding process when sufficient preheating is not possible, as this will minimize the amount of heat input. Another important factor that has a direct impact on the stress-induced at the weld is the cooling rate when the weld is being cooled. As a result of rapid cooling, the welds become brittle and easily cracked due to contraction. By contrast, low cooling reduces the hardening and contraction stress associated with the hardening process.
Selecting the proper welding technique
In theory, any of the common arc welding processes can be used in this process, as long as it facilitates the slow heating and cooling of the weld piece; therefore, we suggest using either manual metal arc welding or flux cored metal arc welding, metal active gas welding, submerged arc welding, or tungsten arc welding.
MAG Welding
As a general rule, MAG welding involves the use of nickel consumables in the welding process. It is recommended that a gas mix consisting of 80% argon and 20% carbon dioxide is used for most applications. Despite the fact that brazing wire can be used, brazing metal is not generally recommended as it will have much lower strength than the casting, which is not recommended either.
Oxy Acetylene Welding
Electrodes are also used in oxyacetylene welding, but instead of an arc generated by the current, an oxyacetylene torch provides the energy. It is possible to oxy-acetylene weld cast iron electrodes, as well as copper-zinc electrodes, using cast iron electrodes.
While acetylene welding cast iron, it is important to take care not to oxidize the cast iron as this will lead to silicon loss and the formation of white iron in the weld. It is recommended to melt the welding rod in a molten weld pool rather than directly on the flame, in order to minimize the temperature gradients within the weld.
Braze Welding
Among the various methods of joining cast iron parts, brazing welding has become increasingly popular due to the minimal impact that it has on the base metal itself. As a result of a welding rod being used, the filler that adheres to the cast iron surface is provided.
Since filler has a lower melting point than cast iron, it doesn’t dissolve in the cast iron but rather adheres to the surface of the iron due to the lower melting point of the filler.
The quality of the filler wetting the base metal surface is critical for this welding technique since the join is determined by the cleanliness of the surface. During brazing, flux is commonly used to prevent oxides from forming.
Liquids that promote wetting facilitate the flow of filler over metal parts. In addition, it removes oxides from the metal parts, allowing the filler to adhere more tightly to them. As well as cleaning metal surfaces, fluxes are used in welding.
Manual Metal Arc Welding
In most cases, shielded metal arc welding (SMAW) is thought to be the best overall method for welding cast iron. However, the right welding rod must be used in order for this type of welding to be successful. It is important to choose the electrode according to the application, the expected color match, and the amount of post-weld machining that needs to be done.
- Iron-based electrodes and nickel-based electrodes are the two main types of electrodes used for manual metal arc welding. When a high carbon martensite weld metal is required, an iron-based electrode is usually used for minor casting repairs or color matching.
- The most commonly used electrodes are nickel alloy electrodes, which are known for their ductility and high tensile strength. Furthermore, nickel electrodes provide a lower strength weld metal, which may also help to reduce pre-heating and HAZ cracking that may occur during the welding process.
- There should always be care taken to limit the amount of melting of the parent metal in all cases. The dilution of the solution will be minimized in this way.
The Techniques for Welding Without Preheating
In some cases, it may be necessary for the repair to be performed without preheating due to the size of the casting or other circumstances. There are times when the part needs to be kept cool, but not cold, in order for it to function correctly.
A temperature increase of 100 degrees Fahrenheit is helpful when casting. The part may be able to be obtained at the temperature of this level by running it for several minutes for a few seconds if it is mounted on an engine. Make sure that the casting is never heated to such an extent that you cannot touch it with your bare hands
The welds should be short, approximately one inch long. This technique entails the use of peening after the welding has been completed. After the weld has been completed and the casting has cooled, remove it from the casting. Neither water nor compressed air should be used to accelerate the cooling process.
The casting may be able to be welded in another area while the weld from before cools down while another area of the casting is welded. It is recommended that all craters be filled in. In addition to the fact that beads should be deposited in the same direction whenever possible, it is also recommended that parallel beads do not line up with one another at the ends.
Cast Welding – Filler Wires or Electrodes
Choosing the correct welding rod is essential for welding cast iron, as mentioned above, although most welding experts will advise you to use nickel rods to avoid any damage to the cast iron.
99 percent of nickel rods
In addition to being more expensive than other options, these electrodes also provide better results than others. Nickel rods with a 99% content produce welds that are machined and work best on castings with a low to medium phosphorus content because they produce welds that are machined. Weld deposits produced by these pure nickel rods are soft, malleable, and easy to shape.
55 percent of Nickel Rods
This rod is less expensive than 99% rods, and these rods are also machinable, which makes them a good choice for repairing thick sections. There is less cracking along the fusion line in these rods because of their lower co-efficient of expansion as compared to the 99% rods. There are several benefits to using ferro-nickel rods when welding cast iron with steel. Alternatively, steel rods can be used, but they are less effective than nickel rods
Brazing Bronze
As an alternative to oxy-acetylene brazing, you can use TIG welders to weld the rods together. As a result, it is a good way to strengthen a crack or join two components that need to be joined, while not causing the cast iron to crack or change its properties in any way.
Steel rods
For minor repairs and fillings, steel rods are the cheapest option of the three and are the best choice for minor repairs. A steel electrode produces hard welds, and because of this, they have to be ground to finish them and are not capable of being machined. Although steel rods have some drawbacks, they are still ideal for color matching and can withstand castings that are not completely clean better than nickel rods despite these drawbacks.
Penning and the cleaning of welding surfaces
There is no doubt that you will have a better weld if you keep the surface clean while welding. There is a possibility that there will be problems welding materials that have been exposed to fumes and oil for a lifetime throughout the casting process, and because of this, welding can be a challenge. Welding cast iron requires you to be aware of some things that you need to be aware about.
It is highly recommended to use welding consumables that are designed for use with contaminated cast iron, such as the MG-289 Cast Iron Welding Alloy rods, in order to create a strong weld.
In order to prevent cracking in the weld, a ball-peen hammer is used to tap the weld as it cools in order to prevent it from cracking. The process of removing a weld should be carried out with caution and only when the weld is susceptible to deformation. However, it is not always necessary to do so, since it is the irregular or rapid heating or cooling of the component that typically results in cracking. In order to get the best results, it is essential that you pre-heat and slowly cool your project.
Post welding heating
When cast iron is allowed to cool down too rapidly, it can lead to cracking as a result. In order to slow down the cooling process, insulation materials can be used or heat can be applied on a periodic basis in order to slow it down. As an example, some methods of cooling the metal work pieces include placing them in an insulating blanket, putting them into dry sand, or even putting them over a wood-fired oven, allowing them to cool as the fire dies down and the heat dies down on them.
What do you mean by In-house welding?
Even though it is recommended to contract out your cast iron welding work to a professional to ensure that the weld is of high quality, it is possible to repair a damaged weld in-house if you prepare it carefully. It is important that you follow the steps of identifying your alloy, preparing the material, and picking the most appropriate welding technique before you begin welding.
Should I preheat or cold-weld?
There is a variety of opinions on whether it is better to weld hot or cold depending on the application. As a general rule, preheating is considered to be one of the best options, but some people feel that welding with a minimal amount of heat will also suffice.
In terms of how to weld cast iron successfully, one of these approaches is recommended, since, unlike most metals, cast iron is extremely brittle and does not have the capability of deforming through bending or expansion and contraction like most metals. Metal always deforms when it is heated or cooled, and if one part of the metal is heated or cooled faster than another, stress is created and cracks develop in the cast iron or welding joint as a result.
- By preheating the surrounding area of the weld, the welding temperature is brought close to the surrounding area of the weld, thereby uniformly changing the whole component and reducing this effect. There are certain characteristics of cast iron that change when the temperature is raised over 1400 degrees Fahrenheit, so it is important not to overheat the component.
- The purpose of preheating the surrounding area of the weld is to bring the welding temperature close to the surrounding area of the weld, as a result of which a uniform change is made in the entire component, thereby lowering the adverse effects of the weld. If the temperature of cast iron is raised above 1400 degrees Fahrenheit, certain characteristics of the component will change, which is why it is very important never to overheat the part when the temperature is raised above 1400 degrees Fahrenheit.
- In order to bring the welding temperature closer to the surrounding area of the weld, the purpose of preheating the surrounding area of the weld is in order to make a uniform change in the entire component as a result of which the adverse effects of the weld are reduced. It is very important to remember that when the temperature of cast iron is raised above 1400 degrees Fahrenheit, certain characteristics of the part will change, which is why, when the temperature is raised above 1400 degrees Fahrenheit, it is very important not to overheat the part.
Experienced welders with experience working on repairing or manufacturing cast iron products on a regular basis should always and only preheat cast iron products before welding. A strong weld is one that is strong from the inside out, so it is more than just one that looks crack less on the outside.
Other types of welding techniques for Cast Iron?
Studding
There are times when studding is used to repair cracks in large castings. A V-shaped groove is a ground in order to remove the fracture in this process. Drilling and tapping holes at an angle are made on both sides of the groove so that studs can be screwed into the holes for a distance equal to the diameter of the studs, with the upper ends of the studs projecting approximately 1/4 of an inch upwards. It is located at a height of 6.4 millimeters above the surface of the cast iron.
- There should be one or two beads sealed around each stud, and then the beads should be tied together by welding metal beads after the beads have been sealed in place.
- There is a need to make short lengths of welds while the weld is hot in order to prevent high stresses or cracks during the cooling process. It is important to allow the metal to cool and clean each bead thoroughly before adding more metal to it.
- Alternatively, a round-nosed tool should be used to chip out the edges of the joint, and then the edge of the joint should be machined to form a U groove in which the weld metal is to be deposited when the studding method cannot be used.
Modification for joint design
The best approach is to use a weld that penetrates completely into the substrate as opposed to one that is partially penetrated. During the welding process, welds that have different thicknesses can result in uneven contraction stresses, as well as uneven expansion stresses.
When welding designs are changed to take advantage of an area where the thickness is constant, welds can be located in an area where welds are advantageous. To support areas that are stressed, you might also want to consider using a backing fillet weld.
Face Groove Grooving
A common technique for preparing a weld groove consists of gouging or grinding grooves into the surface area of the weld groove, in order to fill the grooves with weld beads, then filling the entire joint with weld beads before filling the grooves is sometimes the preferred method.
By using this method, cracking risks are lower because cracks are deflected from their original paths. As long as the stress zone and the fusion line are at a low level, the beads that are in contact with the casting will be deposited first.
