How to Weld Cast Iron:: Features, Types & Uses

Cast iron is difficult to weld but not completely impossible. in some conditions, welding for cast iron is to repair castings, not make castings with other components. The repairs are performed in a foundry where casting is made or can be made for repairing casting errors that are found after parts machining.

Mis-machined cast iron parts use repairing welding if holes are made at the wrong points. Broken cast iron components are repaired through welding. In this post, we will cover details for welding cast iron and is it possible to weld cast iron.

Can You Weld Cast Iron?

• Cast iron welding can be performed but is difficult since it has high carbon. High carbon is in the range of two to four percent, which is 10 times steel.
• At the time of the welding process, this carbon is added to the weld metal or heat-affected area, which increases hardness. in result makes cracks after welding.
• Cast iron comes with carbon and iron in different compositions, and some other elements such as silicon, chromium, nickel, manganese, copper, etc. that increase different features.
• It also has sulfur and phosphorus that make the welding process difficult without cracking.
• Different types of cast iron come with gray cast iron, white cast iron, and malleable cast iron with different welding features.
• These cast irons are weldable, leaving white iron, but the welding process is difficult than welding carbon steel.

Types of Cast Iron

Grey Cast Iron

• This type of cast iron is processed to make graphite in metals. The graphite made with this cast iron comes with high thermal conductivity and increased resistance to damage. It is a famous type of metal and exists in engine blocks, cookware, and manifolds.

White Cast Iron.

• This type of cast iron is heavy and processed in a proper way with some precaution, and graphite content is used for chemical reaction to make iron carbide. This cast iron has wear resistance and provides strength from compression. So it is difficult to weld

Ductile Cast Iron

• This type of cast iron is made with the use of magnesium. It is highly ductile compared to grey cast iron and used for products where high forces are applied, like gears, crankshafts, and suspensions of cars.

Malleable Cast Iron

• This type of cast iron is a processed type of white cast iron, and it is treated to break iron carbide into graphite. the output is a malleable and ductile nature and is used for electrical fittings and machine components.

Welding Types To Weld Cast Iron

Manual Metal Arc Welding (MMA)

• this welding methods also called shielded metal arc welding that is considered as good for cast iron welding, if it performed with accurate welding rods.
• the use of electrode based on applications, the color matching and pist weld machining.
• electrodes types used for manual metal arc wleind are nickel and iron based.
• iron based electrode generated weld metal having high carbon martensite that is limited to small repairing of casting and also for providing color mathcing.
• nickel alloy also reduces pre heating and HAZ cracking with low etrenght weld metal.

MAG Welding

MAG welding is performed through use nickel consumable. the 80 percent argon to 20 percent carbon dioxide gas mixture works for different applications.

Bracing wire is also used but not recommended, since braze metal weak as compared to casting

 Oxy Acetylene Welding

• for arc welding oxy acetylene used as electrode, as compare to producing current. this process performed with oxy acetylene torch for producing heat.
• low heat intensity and slow heating involved in this process causes larger HAZ slow heating is important for avoiding making high carbon martensite in the HAZ.
• low heat intensity for process uses preheating for higher temperature, that is 600 degrees for performing the welding process.
• natural flame used for the welding process

Braze Welding

• Braze welding is a method used for the connection of cast iron components since it has a low effect on base metals.
• The metal rod provides filler that works in the cast iron surface. Due to the lower melting point of filler than cast iron, filler does not dilute through cast iron, but on the surface.
• Before performing welding, perform surface cleanliness as connection is based on filler wetting the surface of the base metals.
• Based on machine design, use flux to avoid oxide creation at the time of brazing.
• liquid provide wetting that helps filler to move over metal components to connected.
• it also clean components of oxides so filler make strong connection with metal components. fluxes used in welding for cleaning metal surface.

Welding Rods for cast iron

the use of weldin rod is main factor for welding of cast iron. different words used that are explained here

 99% Nickel Rods

• this electrode is high cost as compare to other with also provide good results. 99 percent nickles produces welds that machined and work well on castings with low or medium  phosphorous content.
• pure nickel rod make soft, and malleable weld deposit

 55% Nickel Rods

• it is low cost as compare to 99 percent rods and also machneable and used for thick repairs. the low coefficinecy expansion make low fusion line cracks as compare to 99 percent rod.
• it is good to use for welding cast iron with steel. low cost options also exists like steel rods,  but not work like nickles rods

Steel Rods

• Steel rods have a low-cost option and are good to use for minor repairs and filling. Steel electrodes make hard welds, which need extra grinding for finishing and are not machineable.
• But steel rods also provide colour matching and are good for handling castings and are complete than nickel rods.

Challenge for Cast Iron Welding

• cast iron is made with iron carbon alloys having two to 2 to 4 percent carbon content and ten times carbon  in steels.
• there are different cast iron types, but grey cast iron is commonly used.
• white cast iron type is difficult to weld but other types can weld.
• cast iron have hard and strong nature and low ductility so difficult to weld.
• welding of metals causes expansion and contraction in a result of the materials heating and coolings.
• Cast iron has low ductility, molsty in fusion zone, and residual stress of expansion and contraction results in wedng cracking.
• if we weld mild steel, that is dcutile materials so when fusion zone and weld get expnaion and cotnrack the neighboring  material gets flex.
• cast iron not deshapre berfor breaking but get breals. when welds gets cools and pull neiburing cast iron mass can crack.

How to weld cast iron

These steps are involved for welding cast iron Follow these points

Identify the alloy

• the main grades of cas iron are gray iron, ductile iron and malleable iron. white cast iron also exists that is impossible to weld. gray iron is common type of cast iron that is difficult to weld in case when graphite flakes added weld pool and resulting weld metal ebrittlement.
• ductile and malleable iron has low brittle nature sincf od microstructural differences. these two comes with spheroidal carbon microstrcurues based on manufacturing process.

Clean of  casting 

• casting needed accurate preparation before welding removal paint, grease oil and other components on welding locations. after that use heat in proper way and at weld zone for short time that remove trapped gase in base metal.
• use method for cleaning surface to depositing weld flow on it. if impurities are on iron, weld is porous. repeated process utill porosity is not more exists

 Preheat the casting

• heat controlling occurs due to thermal expansion. when metal is heated, it get expand. if complete body warms and expands with same rate, it has stress. it causes stress and crakcin due to heat localization in small heat affect zone.
• preheating reduces theraml graident between casting body and HZ reduces tensile stress resurling of welding.

 welding technique

• in last step select welding method that is good to use for iron alloy. there re 3 common types of process used such as stick, oxy-acetylene, and braze welding, and first one is common
• the stick welding, uses 3 main filler electrodes for cast iron there copper alloy, cast iron covered and nickel alloy.
• The nickel alloy electrodes are common for cast iron since nickel-iron weld is high strength and comes with a low coefficient of thermal expansion that reduces stress and provides high resistance to cracking.
• set electric arc at weld pool as compare to base metal. in this way reduces dilution, use low current setting for reducing heat stress.
• preheat component to about 250 F degrees before welding through copper or electrodes. there is not need of preheating through nickel electrode.

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