Cast iron is an iron-carbon alloy with a carbon (C) content greater than 2.14%. Cast iron is actually a multi-element iron alloy mainly composed of Fe, C and Si. Cast iron can be divided into gray cast iron (HT), malleable cast iron (KT), ductile cast iron (QT), cast iron with compacted graphite (RT) and white cast iron (BT).
Common types of gray cast iron include HT100, HT200, HT250, HT300 and HT350. Common types of ductile cast iron include QT400-18, QT400-15, QT450-10, and QT500-7.
The application of cast iron welding mainly occurs in the following three situations:
1) Repair by welding of casting defects.
2) Repair by welding of damaged cast iron finished parts.
3) Component production, which refers to the production of components by welding cast iron parts (mainly ductile cast iron) together with cast iron parts, various types of steel or non-ferrous metal parts.
Commonly used methods for welding cast iron include shielded metal arc welding (SMAW), CO 2 gas shielded welding, gas welding, gas flame brazing, manual metal arc welding (MMAW), and spraying of dust with a gas flame.
Among these methods, SMAW is the most commonly used. To meet different requirements, cast iron welding materials used in SMAW are classified into three main types based on the type of weld metal: iron-based, nickel-based and copper-based.
1. Gray Cast Iron Welding
1. Welding characteristics of gray cast iron
Gray cast iron has certain characteristics in terms of chemical composition, including high carbon content and high levels of sulfur and phosphorus impurities. This increases the sensitivity of the welded joint to changes in cooling rate and its susceptibility to cold and hot cracking.
In terms of mechanical properties, gray cast iron is characterized by low strength and practically no ductility. These two aspects, combined with the rapid cooling rate during the welding process and the significant welding stress caused by uneven welding heating, result in poor weldability of cast iron.
The main problems are twofold: the welded joint is prone to the formation of white iron and hardened structures, and it is also susceptible to cracking.
( 1 ) Formation of white iron and hardened structures in welded joints
When welding gray cast iron, the small size of the weld pool and its short existence time, combined with the internal heat conduction of the cast iron, results in a much faster cooling rate in the weld and the adjacent heat-affected zone in compared to cooling. rate of castings in sand mold.
As a result, a large amount of cementite will be formed in the weld and partially molten zone, leading to the formation of a white cast iron structure. The areas where the white iron structure is formed in the welded joint are mainly the weld zone, the partially molten zone and the austenite zone.
The problem of white iron formation in gray cast iron joints mainly refers to the tendency of the weld and the partially molten zone to form a white iron structure. This is mainly due to the high tendency of the joint to be excessively cooled during the welding process, which affects the cast iron graphitization process.
The presence of white iron structure in cast iron joints not only causes processing difficulties, but also leads to the formation of defects such as cracks. Therefore, certain measures must be taken to minimize the conditions for their formation and create favorable conditions for graphitization of the joint.
The main approach is to change the chemical composition of the weld or decrease the cooling rate of the weld to prevent the formation of white iron structure.
Furthermore, the use of brazing methods, where the base material is not melted, can fundamentally avoid the formation of white iron structure in the partially molten zone. This is another approach to prevent the problem of white iron formation in joints.
(2) Welding cracks
Cracking is a common defect in welding gray cast iron. Welding cracks in cast iron can be classified into two categories: cold cracks and hot cracks.
1) Cold cracks: Cold cracks when welding gray cast iron normally occur in the weld zone and the heat-affected zone. Cold cracks are most likely to occur in welds where the filler metal is cast iron itself.
When using different welding materials to create austenite, ferrite, or copper-based filler metal welds, cold cracking is less likely to occur due to the better ductility of the weld metal and the use of appropriate cold welding processes.
The temperature at which cracking occurs in cast iron welds is generally below 400°C. Cracks are often accompanied by an audible sound of brittle fracture. These types of cracks often occur in longer welds or when repairing large defects in high-stiffness cast iron.
The most effective way to prevent crack formation is to preheat the entire weld (550-700°C) to reduce temperature differentials and reduce welding stress. In some cases, using the heat dissipation method to reduce stress in the repair area can also effectively prevent crack formation.
Cold cracks in the heat-affected zone typically occur in areas with high cementite and martensite content. In some cases, they can also occur in the heat-affected zone, slightly away from the fusion line. When welding thin-walled cast iron components (5-10 mm), cold cracks may also occur in the heat-affected zone, slightly away from the fusion line.
It is important to note that the specific preheating temperature and other measures to prevent cracking may vary depending on the specific cast iron material, thickness and welding conditions. Therefore, it is recommended to consult welding experts and refer to relevant welding standards and guidelines for proper procedures.
Process measures can be taken to reduce stress in the welded joint and prevent the formation of cementite and martensite. Preheat welding can be used to prevent the cold cracks mentioned above from occurring. When using cold arc welding, adopting the correct cold welding process to weaken the stress state of the welded joint is beneficial in preventing cold cracking.
The use of welding materials with lower yield strengths and good plasticity is also beneficial in preventing cold cracks. When repairing thick and large components with crack defects, where the groove is large and multiple layers of welding are required, the accumulated welding stress is high.
To prevent cold cracks in the heat-affected zone from turning into delamination cracks, the wire feeding method can be used on both sides of the welding groove.
2) Hot cracks: When the weld is cast iron, it is not sensitive to hot cracks. However, when using low-carbon steel electrodes and nickel-based cast iron electrodes for cold welding, the weld is more prone to crystalline cracks, which belong to hot cracks.
When welding gray cast iron, there is a significant tendency for cracks in the welded joint. This is mainly related to the properties of the cast iron itself, welding stress, joint structure and chemical composition.
To prevent the formation of cracks during welding of cast iron, measures such as reducing welding stress, changing the welding alloy system and limiting the inclusion of impurities from the base material in the weld are mainly adopted in production.
2. Welding process for gray cast iron
Based on the welding characteristics of gray cast iron, which are the tendency to form white iron and the occurrence of cracks, it is necessary to start from preventing these defects and consider multiple factors when selecting welding methods and developing a reasonable welding process.
(1) Fusion welding of homogeneous welds (cast iron type):
Fusion welding of homogeneous welds can be done using arc welding, semi-hot welding, gas welding and cold arc welding.
1) Arc welding and semi-hot welding:
Preheat the entire weldment or defective area to 600-700°C and then perform repair welding. After welding, adopt a gradual cooling cast iron repair process known as hot welding. When the preheating temperature range is 300-400°C, it is called semi-hot welding.
Both hot arc welding and semi-hot arc welding have two types of electrodes. One type is graphite cast iron electrode with cast iron core (Z248), and the other type is graphite cast iron electrode with steel core (Z208).
Z248 electrode is mainly used to repair defects in thick and large castings. The welding core of this type of electrode is a φ6-φ12mm cast iron bar, coated with a graphite-forming flux. The large diameter of the electrode with a cast iron core allows the use of high welding currents, which speeds up the welding process and reduces the welder's labor intensity.
The Z208 electrode uses a low carbon steel (H08) core and is coated with a strong graphite-forming flux. The resulting weld is of the cast iron type. Although the welding core is made of low carbon steel, the addition of graphite-forming substances to the flux ensures that the weld obtains similar composition and structure to gray cast iron under hot and semi-hot welding conditions.
During hot arc welding, the casting or local repair area is generally preheated to 600-700℃ before welding. After welding, the joint is isolated and cooled slowly, significantly improving the stress state of the joint and effectively preventing the formation of cold cracks.
Due to the high preheating temperature and slow cooling in hot welding, the joint is completely graphitized, which completely prevents the formation of white iron and hardened structures. The specific hot welding process is as follows:
a) Preheating: For castings with complex structures, where the repair area has high rigidity and the weld has limited freedom for expansion and contraction, it is recommended to carry out general preheating.
For castings with simple structures, where the repair area has low rigidity and the weld has some space for expansion and contraction, such as defects on the edge of the casting or small areas of fracture, local preheating can be used.
b) Pre-welding cleaning: Before hot arc welding, the welding area of the casting must be cleaned and prepared by removing any dirt or contaminants. If there is oil contamination in the defect area of the casting, it can usually be removed by heating with an oxy-acetylene flame.
Then, depending on the nature of the defect, tools such as hand grinders, chisels or pneumatic chisels can be used for further processing. When creating the groove, it should be ground or chamfered until there are no defects, and the groove should have a smooth bottom and a slightly wider opening to facilitate operation and ensure welding quality.
c) Molding: For corner areas and penetrating defects, to avoid loss of molten metal and ensure the desired shape of the weld, molding should be done in the welding area before welding. The shape and dimensions of the mold are shown in Figure 5-1.
Molding materials such as molding sand mixed with glass of water or yellow clay can be used. It is preferable to place heat-resistant graphite pieces on the inner wall of the mold to prevent the molding material from melting or collapsing due to heat. The mold must be dried before welding.
During welding, in order to maintain the preheating temperature and reduce the working time at high temperature, it is necessary to complete the welding in the shortest possible time. Therefore, it is recommended to use high current welding, long arc welding and continuous welding.
a) Repair of medium defects
b) Repair of defects on edges
In order to reduce the preheating temperature and improve working conditions, it has been found in practice that adequately increasing the graphitization capacity of the weld seam and using a preheating temperature of 300-400°C, overall or locally, it can achieve good results in the welding of castings with low rigidity.
In general, Z208 or Z248 cast iron welding rods can be used. The semi-hot welding process is basically the same as the hot welding process, which involves high current, long arc, continuous welding and post-welding insulation and slow cooling.
Due to the lower preheating temperature in semi-hot welding compared to hot welding, the plastic deformation of the casting during heating is less pronounced.
Therefore, when the repaired area has greater rigidity, it is less subject to deformation and increased internal stress, which can lead to defects such as cracks in the joints. Therefore, semi-hot arc welding can only be used for repair areas with lower rigidity or simpler casting shapes.
2) Gas welding:
The temperature of the oxyacetylene flame is much lower than that of the arc and the heat is not concentrated, making it suitable for repairing thin-walled castings. To repair defects in thin-walled, highly rigid parts, in order to reduce welding stresses and avoid cracks, it is advisable to use the hot welding method by gas welding with general preheating of the part.
The preheating temperature should be around 600-700°C, and post-welding slow cooling measures should be taken.
For gas welding of cast iron, welding materials mainly consist of welding wire and gas welding flux. The welding wire models are RZC-1 and RZC-2, with slightly higher carbon (C) and silicon (Si) contents compared to hot welding. The unified brand for gas welding flux used in welding cast iron is CJ201.
Before gas welding, the casting must be cleaned, and the pre-welding cleaning and preparation work is essentially the same as that of electrode arc welding. Mechanical methods can usually be used to prepare the bezel. When the cross-section of the casting is very small or when it is not possible to create a chamfer using mechanical methods, oxygen cutting can also be used to directly create the chamfer.
During gas welding, larger welding torches and nozzles should be selected according to the thickness of the casting in order to increase the flame energy and heating speed. Generally, a neutral flame or a weak carburizing flame should be used for gas welding, and an oxidizing flame should not be used.
This occurs because an oxidizing atmosphere can increase the loss due to burning of carbon, silicon and other elements in the weld pool, affecting the graphitization process of the weld. To avoid loss of molten metal from the weld pool, welding should be carried out in a horizontal position as much as possible.
After welding, the casting can cool naturally, but it should not be placed in a place with air circulation to accelerate cooling, as this can lead to the formation of white spots and cracks.
For smaller castings, the cold welding method can be used if defects are located in corners or in areas of lower rigidity. The feature of this method is that separate preheating is not required.
Welding can be performed by fusing the surrounding area of the bezel with the flame of the welding torch. After welding, the joint can be cooled naturally to obtain a defect-free and crack-free weld.
However, when the defects are located in the center of the casting, or if the joint has greater rigidity or a more complex shape, the cold welding method may not be effective. In these cases, the hot welding method with a preheating temperature of 600-700°C or the “heat and reduce the stress zone” method must be used. The schematic diagram of the heating and voltage reduction zone is shown in Figure 5-2.
3) Cold arc welding:
The characteristic of cold arc welding is that the welded part does not require preheating before welding. Therefore, cold arc welding has many advantages such as good working conditions for the welder, low welding repair cost, short repair process and high efficiency.
It is more suitable to use cold welding for large castings that are difficult to preheat or for processed surfaces that cannot be preheated. Therefore, cold welding is a development direction in gray cast iron welding.
Under cold welding conditions, there are two approaches to solve the problem of white spots: first, further improve the graphitization ability of the weld seam; second, to increase heat input during welding.
For example, using large diameter welding rods, high current continuous welding processes can be employed to slow the cooling rate of the welded joint. This process also helps eliminate or reduce the occurrence of martensitic structure in the heat-affected zone.
At present, the grade of cold welding rod for homogeneous welding is also Z208 and Z248, but the specific formulation differs from that of hot welding rod. Due to the faster cooling rate during cold welding, the carbon and silicon content of the cold welding rod for homogeneous welds should be higher than that of the hot welding rod.
Under cold welding conditions, to prevent the occurrence of white spots and hardened structures in the welded joint, it is necessary to decrease the cooling rate of the welded joint. To achieve this, large diameter welding rods and high current continuous welding processes must be used.
However, when the repaired defect area is less than 8 cm2 and the depth is less than 7 mm, the small volume of the weld pool and rapid cooling may still result in white spots on the welded joint. If possible, enlarging the defect area can eliminate white spots.
During welding, you can use a DC reverse polarity power source, or an AC power source, with high current and long arc, welding continuously from the center to the edge. After filling the bevel with solder, the arc must not be interrupted. Instead, the arc must be moved along the edge of the weld pool, close to the sand mold, to form the weld bead.
Generally, the height of the weld bead should exceed the workpiece surface by 5-8 mm. By allowing heat from the arc to be transferred to the semi-molten zone through the top layer of the weld, it can remain in an incandescent state for a certain period of time, slowing the cooling rate and allowing sufficient graphitization of the weld. . It also prolongs the presence of the semi-molten zone at the top of the weld, which facilitates the diffusion of carbon into the weld, reducing or eliminating white spot structures.
Furthermore, during cold welding of homogeneous welds, the arc must immediately cover the weld pool after welding to provide insulation and slow cooling.
Cold arc welding with cast iron electrodes is simpler than the hot arc welding process and has lower welding costs. When repairing larger defects (with an area greater than 8cm2 and depth greater than 7mm), as long as the appropriate process is used, the maximum hardness of the weld after welding does not exceed 250HBW and has good machinability.
(2) Cold arc welding of heterogeneous weld beads (non-cast iron)
Heterogeneous weld seams, also known as non-cast iron weld seams, are commonly used in cast iron welding. Cold arc welding is the most commonly used method of welding cast iron. The welding process is greatly simplified as no preheating is required for the castings, which not only reduces welding costs but also improves the working conditions of welders.
Furthermore, it has a wide range of applications, allowing welding in all positions and high welding efficiency. Therefore, cold arc welding of heterogeneous weld beads is a highly promising welding process.
1) Materials for cold arc welding of heterogeneous weld beads
At present, China has developed a variety of series of non-fused weld seam cast iron electrodes. In terms of welding methods, there are wire planting methods and pad welding methods.
Wire planting method: This method involves using carbon steel screws to secure the weld seam and the unwelded heat-affected zone of the casting, preventing the occurrence of cracks and improving the ability of this area to withstand impact loads .
Pad welding method: When repairing thick-walled components with cracks, a low-carbon steel pad is placed inside the groove, and on both sides of the pad, a cast iron electrode with high crack resistance and good welding performance resistance (such as Z438, Z117 electrodes, etc.) is used to weld the base metal to the low carbon steel pad.
Under cold arc welding conditions, the cooling rate of the joint is relatively high, which makes the problem of porosity and cracking more prominent. Cold welding of heterogeneous weld beads is mainly achieved by adjusting the chemical composition of the weld bead to improve the structure and properties of the joint. Non-cast iron weld seams can be classified into steel-based, copper-based and nickel-based types based on the properties of the weld metal.
The classification of steel-based arc welding cold welding electrodes is as follows:
a) Strongly oxidizing cast iron electrode EZFe-1 (Z100): This electrode uses a low carbon steel core (H08) and adds an appropriate amount of strong oxidizing substances into the flux jacket. The objective is to increase the oxidizing property of the slag, allowing it to react with the weld pool and oxidize and burn carbon, silicon and other elements of the base metal, in order to obtain a carbon steel weld bead with good plasticity.
b) EZFe-2 carbon steel electrode (Z122Fe): This electrode is an iron powder type electrode with a low carbon steel core, with titanium-calcium type flux coating. A certain amount of low-carbon iron powder is added to the flux coating. The addition of low-carbon iron powder still aims to reduce the carbon content.
c) EZV high vanadium cast iron electrode (Z116, Z117) for high vanadium steel weld beads: The high vanadium cast iron electrode uses a low carbon steel core (H08) and adds a large amount of vanadium iron in flux coating, resulting in steel structure with high vanadium content in the weld.
The purpose of adding iron vanadium to the weld seam is to take advantage of vanadium's strong ability to form carbides. By changing the shape of carbon in the weld seam, the plasticity of the weld seam is increased, thereby preventing the formation of white mouth and hardened structures in the weld seam and improving its crack resistance.
Currently, there are three types of nickel-based cold arc welding electrodes, which have certain differences in performance due to variations in alloy content. Under certain welding current conditions, the higher the nickel content in the weld seam, the narrower the width of the white mouth layer of the semi-molten zone and the better the mechanical machinability of the joint. Therefore, pure nickel weld beads have the best machinability.
a) EZNi pure nickel electrode (Z308): The core of pure nickel electrode is made of pure nickel. Due to its high nickel content, when using low current to repair cast iron, the white mouth layer in the semi-molten zone of the joint is minimized, with a width of approximately 0.05-0.08mm, and is distributed discontinuously, the which is beneficial for mechanical machining.
The strength of pure nickel weld beads is close to that of gray cast iron and they have good ductility, which makes them resistant to cold cracking.
However, nickel is a precious metal, and pure nickel electrode has the highest nickel content and is the most expensive (about 30 times the price of low-carbon steel electrodes), so it should not be used in large quantities in welding.
b) EZNiFe Nickel-Iron Electrode (Z408): The core of the nickel-iron electrode is made of a nickel-iron alloy. Nickel-iron weld beads have higher strength, reaching more than 400MPa, and good ductility, making them suitable for welding high-strength cast iron.
Because the performance of nickel-iron electrode is superior to that of pure nickel electrode and its price is the cheapest among nickel-based electrodes, it is widely used in production.
c) EZNiCu Nickel-Copper Electrode (Z508): The core of the nickel-copper electrode is made of a nickel-copper alloy, also known as Monel electrode, which is one of the first cast iron electrodes used. However, this type of electrode was gradually replaced by nickel-iron electrodes.
There are several forms of copper-based electrodes:
a) Iron powder electrode with copper core (Z607): The flux coating is low hydrogen type and is mainly used for welding repairs on non-machined surfaces.
b) Copper core iron sheath electrode (Z616): A steel strip tightly wraps a pure copper core using a wire drawing device. It is coated with a low hydrogen alkaline flux coating and there are also titanium-calcium type flux coatings such as Z612. It is also mainly used for welding repairs on non-machined surfaces.
c) Austenitic steel-copper electrode: Copper-steel electrodes have good resistance to cracking and the material is easy to handle. Therefore, they still have certain applications in cast iron welding.
2) Cold arc welding process for heterogeneous weld beads (non-cast iron). The key points of the cold arc welding process for heterogeneous weld beads can be summarized in four sentences:
- Proper prep work is essential.
- The welding current must be adequately low.
- Welding must be done in short, intermittent segments.
- Immediately after welding, lightly hammer the welded area.
There are two commonly used methods for cleaning castings. One method is mechanical cleaning, which involves the use of tools such as grinding wheels, wire brushes or flat paddles. The other method is chemical cleaning, which involves washing the casting with chemical solvents such as trichloroethylene, gasoline or acetone.
When the thickness of the casting or the depth of the defect is greater than 5 mm, a groove must be prepared and the surface of the groove must be as flat as possible.
When using welding materials other than cast iron for cold arc welding, it is important to use an appropriate minimum current to ensure arc stability and full penetration. Small diameter electrodes should be used for welding.
In order to reduce the welding heat input, minimize stress and decrease the width of the semi-molten zone, the welding speed should be increased appropriately without making any lateral oscillations. The welding process should involve welding of short segments, intermittent and scattered welding, and post-weld hammering.
(3) Brazing of gray cast iron
Brazing is advantageous for preventing the occurrence of white mouth in cast iron joints, as it does not melt the base material, providing excellent machinability for the joints.
Both nationally and internationally, oxyacetylene flame brazing is commonly used for cast iron. In the past, HL103 brass brazing filler metal was commonly used, and borax can be used as brazing flux.
2. Typical examples of cast iron repair welding
1. In a steam distribution chamber of a gas turbine in a certain factory, cracks appeared due to prolonged exposure to high-temperature steam.
The component material is gray cast iron. Cold arc welding was adopted to repair the part, using J506 and Z308 rods to repair the joint, with excellent results. The specific welding process is as follows:
(1) Pre-welding preparation: Fix the workpiece, use a grinding wheel to create a V-shaped groove at the crack location, and heat the groove and its surroundings with a gas welding torch. After cooling, clean the groove surface and its surroundings.
(2) Welding: Use J506 welding rod to deposit a transition layer along the groove surface and 20mm on each side, as shown in Figure 5-3. Then use a φ3.3 Z308 welding rod for back welding of the bottom layer. Finally, use a φ4.0 Z308 welding rod for step welding, as shown in Figure 5-4. The length of each weld bead must be controlled within 25 mm. Immediately after completing each section, perform hammering to release welding tension.
2. In a certain factory, cracks appeared on the base of a lathe, which is made of gray cast iron.
Thermal arc welding was used for repair, with Z248 welding rod for homogeneous weld seam. The welding process is as follows:
(1) Pre-welding preparation:
- 1) Chamfer preparation: The chamfer angle should be 70° to 80°, with a V-shaped groove. If the defects are not large enough, they may be artificially enlarged to an area of not less than 3 to 4 cm2 and a depth of not less than 10 cm to facilitate the increase in temperature in the repair area and reduce the hardness of the weld. The groove must be thoroughly cleaned.
- 2) The welding rod should be dried at a temperature of 200 to 300 ℃ before use and kept warm for 1 to 2 hours.
- 3) Preheating should be carried out in the welding area, with a preheating temperature of 600 to 700 ℃.
(2) Key points of welding operation:
- 1) Create the arc in the center of the defect and use short arc welding. Continue welding until it extends 4 to 6 mm beyond the surface of the workpiece.
- 2) Use the hot peening method (welding in a red-hot state) to reduce the shrinkage stress of the weld.
- 3) During the welding process, if defects such as gas holes or slag inclusions are found, they must be treated immediately. If cracks are discovered, they must also be treated immediately after welding and must not be repaired after the weld has cooled.
- 4) After welding, immediate insulation or local flame heating should be applied to obtain gradual cooling and eliminate stress.
3. Welding of ductile cast iron.
1. Ductile cast iron welding characteristics:
The difference between ductile cast iron and gray cast iron is the addition of a certain amount of nodulizing agent during the melting process. Common nodulizing agents include magnesium, cerium, yttrium, etc. The graphite in ductile cast iron exists in a spherical shape, which significantly improves its mechanical properties.
The welding characteristics of ductile cast iron are similar to those of gray cast iron, but it also has some unique characteristics, which are mainly manifested in two aspects:
1) Ductile cast iron has a greater tendency to white mouth formation and quench hardening compared to gray cast iron. When welding ductile cast iron, homogeneous weld beads and partially molten zones are more prone to white mouth formation, while the austenite region is more likely to exhibit martensitic structure.
2) Due to the higher strength, plasticity and toughness of ductile cast iron compared to gray cast iron, the mechanical performance requirements for welded joints also increase. It is often necessary to match the strength level of the ductile cast iron base material.
2. Ductile cast iron welding process:
(1) Fusion welding process for homogeneous weld beads:
1) Gas welding:
When gas welding ductile cast iron, the continuous welding time should not exceed 15 to 50 minutes, as it may lead to the formation of graphite flakes in the weld seam, resulting in a reduction in mechanical properties. Gas welding is primarily used for welding repairs on thin-walled ductile cast iron components.
For gas welding of ductile cast iron, there are two types of welding wires: light magnesium rare earth alloy and yttrium based heavy rare earth. The flux used for gas welding of ductile cast iron has the same composition as the flux used for gas welding of gray cast iron, and the unified designation for the flux used for welding cast iron is CJ201.
Cold or hot welding can be used, with a preheating temperature range of 500 to 700 ℃ for hot welding. After welding, it must be insulated and cooled slowly. The gas welding process for ductile cast iron is essentially the same as that for gray cast iron.
2) Electrode arc welding:
Ductile cast iron electrode arc welding can also be categorized into cold welding and hot welding. For cold welding, nickel-iron electrodes and electrodes with a high vanadium content are used. When the composition of the weld seam is ductile cast iron, hot welding is commonly employed. Commonly used ductile cast iron welding electrodes are shown in Table 5-31, including Z258, Z238, Z238F and Z238SnCu.
Use continuous and high current welding process. For moderate defects, the weld must be continuously filled. For larger defects, welding must be done in sections, advancing gradually to ensure greater thermal input in the repair area.
To repair larger defects in rigid sections, a preheating and stress reduction process must be employed. Preheating to 200 to 400°C before welding, followed by slow cooling after welding, to prevent cracks from occurring.
(2) Arc welding of heterogeneous weld beads – Cold welding:
For arc welding of heterogeneous weld beads in ductile cast iron, the main types of electrodes used are nickel-iron electrodes, such as Z408, Z438, and high-vanadium electrodes, such as Z116, Z117.
Table 5-31: Types and applications of commonly used cast iron welding electrodes
| Welding Electrode Model | Welding Rod Class | Types of Flow Coating | Metal Types of Welding Wire | Scope of application |
| EZFe-1 | Z100 | Oxidizing type | Carbon steel | Generally used to repair unmachined surfaces of gray cast iron parts. |
| EZV | Z116 | Type of sodium with low hydrogen content | Steel with high vanadium, carbon and sodium content | Used to repair high-strength gray cast iron parts and ductile iron parts. |
| EZV | Z117 | Low hydrogen and potassium type | ||
| EZFe-2 | Z122Fe | Titanium Calcium Type Iron Powder | Metal Types of Welding Wire | Commonly used to repair unmachined surfaces of gray cast iron parts. |
| EZC | Z208 | Type of graphite | Cast iron | Generally used to repair gray cast iron. |
| EZCQ | Z238 | Ductile Iron | Used to repair ductile iron. | |
| EZCQ | Z238SnCu | Used to repair ductile iron, vermicular cast iron, alloyed cast iron, malleable cast iron and gray cast iron. | ||
| EZC | Z248 | Cast iron | Used to repair gray cast iron parts. | |
| EZCQ | Z258 | Ductile Iron | Generally used to repair ductile iron, Z268 can also be used to repair high-strength gray cast iron parts. | |
| EZCQ | Z268 | |||
| EZNi-1 | Z308 | Pure Nickel | Generally used to repair important thin-walled gray cast iron parts and machined surfaces. | |
| EZNiFe-1 | Z408 | Nickel-Iron Alloy | Used to repair important parts of high strength gray cast iron and ductile iron. | |
| EZNiFeCu | Z408A | Nickel-Iron-Copper Alloy | Used to repair important gray cast iron and ductile iron parts. | |
| EZNiFe | Z438 | Nickel-Iron Alloy | ||
| EZNiCu | Z508 | Nickel-Copper Alloy | Generally used to repair gray cast iron parts with low strength requirements. | |
| Z607 | Type of sodium with low hydrogen content | Copper-Iron Alloy | Generally used to repair unmachined surfaces of gray cast iron parts. | |
| Z612 | Type Titanium Calcium |
