Can You Weld Cast Iron With A Wire Feed Welder?

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You'll need to be careful when welding cast iron metals like exhaust manifold with MIG welds. It's easier to weld cast iron with nickel rods like ASTM B160 from Small Parts, but it's a difficult process with MIG welders. By preheating the cast iron metal with a torch, such as Cadrim Torch, it prepares it for the next welding phase. This guide shows welding enthusiasts the 'know-how' of fixing cast iron with wire feed welders.

What Are Cast Irons

They are less malleable metals (than steel) with low tensile strengths. Also, this type of metal comes from the family of iron-carbon ( iron, carbon, and steel) alloys. In their molten state, it's easy to use form molds and casts with irons. Apart from excessive application of heat, cast irons are prone to cracks under tensile load. If cast iron materials could only expand when heated (or stressed), they would be easy to weld.

Why Is It Difficult To Weld Cast Iron Pieces?

  • Consider the chemical composition of base metals. It's an important factor in choosing any welding process.
  • Usually, cast iron's tensile strength can't hold its material under intense heat. So, applying mild heat or pre-heating the metal can prevent further cracks.
  • Since cast irons contain carbon (between 2% - 4%), they are very brittle and crack easily. When heat intensity increases, the carbon content in cast iron becomes high and emits flakes of graphite.
  • Thermal stress differential can also trigger a difficult process when using wire feed welders. However, it might be hard to weld cast iron, but not impossible at all.

Is Pre-heating Important

When you weld cast iron materials with wire feed MIGs, they often become brittle. Generally, metals with weak tensile strength are affected by thermal contraction easily. It will be counter-productive to shrink and crack the cast iron's crevice with excess heat. Instead, use filler rods to pre-heat, and braze the cast iron piece.

Basic Steps For Welding Cast Iron Pieces

Identify the right alloy and select the right MIG-welding filler rod (electrode). A welder might experience different levels of difficulty during the weld. This condition depends on the type of cast iron alloy that's involved. Let's see some common types of cast iron alloy. 

Grey Cast Iron

During manufacturing, these types of (grey) cast irons precipitate carbon into graphite flakes. The grey cast iron has a molecular structure that makes it easier to weldable than white cast irons. Also, it's are more ductile and contains more carbon content than mild steel. Welders have to be observant during work because graphite flakes might drop into the weld pool. This contamination leads to embrittlement of weld metals.

White Cast Iron

White cast irons are popular for their characteristic of high cooling rates, and being unweldable. However, they don't precipitate their rich content of carbon out as graphite. Like grey cast irons, they are brittle and have tough structures. These types of cast iron contain (a mix of iron and carbon atoms) iron carbide elements.

Clean the casting properly, and bevel its fracture with a cutting torch. You can use a beveling machine if the torch is not available. This process ensures the removal of rust, grease, and paint surfaces from the weld zone.

Pre-heating

The technique for pre-heating cast iron is delivering low heat and allowing it to cool slowly.  Set the temperature, and pre-heat without using the arc does to damage the cast iron. Be careful as you raise the cast iron's temperature slowly. However, large cast-iron pieces need to be preheated around the weld zone. If your cast iron piece is small, wrap it in a thermal blanket and pre-heat.

Select A Suitable Welding Technique

Choose an appropriate welding process for cast irons. Common techniques include brazing, stick, and oxy-acetylene welding. When welding cast irons, the arc should face the weld pool and not the base metal.  Operators need a low current (electricity) and a slow movement of the hand to weld cast iron finely. 

Focus on every inch of the weld zone, and target differs spots after tacking your welds. Also, let the hot iron cool for about 50 seconds between (1 to 2 inches) segments. Otherwise, the heat might be excessive and thermal stress on the metals. Don't forget to clean the flux with a wire brush if you weld with flux-cored wire.

Rod selection

It's important to select the right electrodes (rods) for cast iron welds. Usually, the electric arc applies heat through electrodes and melts the welding zone to form a fusion. 

Copper and Nickel alloys are common types of electrodes for welding cast iron metals. However, nickel-iron welds have lower thermal expansion coefficients. They are the strongest bonds that increase the metal's resistance to cracks.

Disadvantages Of Using The Wrong Welding Process On Cast Iron Materials

  • There's a chance of creating more cracks on the cast iron.
  • It's a difficult process that requires the application of flawless welding techniques.
  • Without applying short welds, the cast iron might get very hot and break into pieces.
  • They will snap and disintegrate under stress and tensile load

How To Weld Cast Iron Step By Step

Final Note

Operators need high-level skills and patience to fix crevices on cast iron pieces. Regardless of your welding machine, every welding task needs to be perfect. If you are considering wire feed MIGs for cast iron welds, you'll need to understand expansion and contraction levels the base metal. Don't forget to apply the techniques that we provided in this guide.

Richard Boyer
 

Richard wants to educate you, inform you, and prepare you to make the best decision you can concerning welding related items.

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