What Kind of Welding Rod to Use on Cast Iron?

Cast-iron repair is a little bit complicated because it wants to crack from the welding. Cast-iron electrode comes with special Graphite rich flux, which graphite chemically bonded up the carbon content in the cast-iron. Also, Choosing the electrode for cast iron mainly depends on your budget, machine-ability, and welding process. Many professionals and experienced welders use pure nickel and nickel-iron electrodes to welding cast iron. Some use 55% nickel rod.

So, What Kind of Welding Rod to Use on Cast Iron? Nickel-alloy is the best for welding cast iron. According to New Hampshire Materials Laboratory Inc. Nickel-alloy has a lower coefficient of thermal expansion that gives you stronger welds and comes with less welding stress and high resistance to cracking.

What’s The Best Rod When Welding Cast Iron?

There are three types of electrodes for welding, that can able to weld cast-iron, that is:

1. 99% Nickel-rods
2. 55% Nickel-rods
3. Steel Rods
   

01. 99% NICKEL RODS

99% Pure Nickel is expensive. But it's more user-friendly, due to its lower melting point compared to the cast iron, and filler does adhere to the surface. It does not dilute with the cast iron.

02. 55% NICKEL RODS

This is the best cheap option. For cast-iron welding, 55% Nickel rod gives you stronger welds than 99% Nickel rod. Because, it is more ductile iron and more tolerant of phosphorous. But keep in mind, don't overheat the base metal when welds by the 55% Nickel rods, because the braze does not adheres to the surface. It works well on casting with low or medium phosphorous content.

03. STEEL RODS

This is one of the cheapest options for welding cast iron. It's suitable for simple repair and filler. Moreover, they are not machineable and required some extra grinding after finishing the weld. They also produce a hard weld. But they are user-friendly with the ARC welder for the weld metal.

How to choose the welding rod for cast iron?

It is necessary to find an appropriate electrode for welding cast iron. But finding the right welding rod is challenging for a beginner welder or professional welders. However, if you have good knowledge about Weld Metal Chemistry and electrode specification, that's will have no issue to choose the right option for you.

For your better understand here I give you Weld Metal Chemistry and electrode specification data:

The Right Type of Metal

Before welding cast iron you have to ensure, is it weldable or not. It has more than 2% carbon, 1 to 3% silicon, and up to 1% manganese. Cast iron is generally inexpensive and easy to give any shape. Moreover, they have graphite flakes which are causes for gray color inside the cracks.

Unfortunately, all cast iron grades are not weldable, some special precautions required when welding your weldable cast iron.

According to mechanical properties and weldability, it can be divided into 4 groups, such as Grey cast iron, Malleable irons, White cast irons, SG graphite. On the other hand, malleable iron can be divided into three classes. Those are Blackheart, Whiteheart, and Pearlitic irons.

From this grouping some are weldable and some are not recommended for welding. However, SG graphite is readily welded. Also Grey cast irons, Blackheart, Whiteheart, Pearlitic irons can be welded. Moreover, White cast iron is not recommended for welding.

Cast Iron Welding Rod Specification

I have already discussed the cast-iron electrode, which is appropriate for welding cast iron. However, before finalizing any electrode for welding cast iron, you have to know the Typical Weld Metal Chemistry, Typical Mechanical Properties of Weld Metal, Sizes, and Recommended Current Ranges.

Here, I give you all the necessary specifications.

1. 99% NICKEL RODS (AWS/SFA 5.15 Eni-Cl)
2. 55% NICKEL RODS (AWS/SFA 5.15 Class ENiFe-Cl)
3. Steel Electrode (AWS/SFA 5.15 EST)

01. 99% NICKEL RODS Specification (AWS/SFA 5.15 Eni-Cl):

Nickel alloy electrodes are recommended for weld thin cast iron in all position welding. It is pure nickel approximately 99% nickel and the weld deposit is soft. That can be shaped, milled, drilled, or tapped, while the color is similar to the cast iron. Moreover, Alloy Nickel 99 electrodes are suitable for weld cracks or porous castings, also they can weld dissimilar metals such as carbon steel and alloy.

This 99% nickel electrode can commonly weld thin plates, frames, housing, machinery parts.

• Typical Weld Metal Chemistry (%)

1) C --> 1.000,  2) Si --> 0.700,  3) Mn --> 0.200, 4) P --> 0.005,

5) S --> 0.005, 6) Fe --> 3.000, 7) Ni --> Balance

• Typical Mechanical Properties of Weld Metal (As Welded) 

Tensile strength (psi) ......................... 50,000

Yield strength (psi)............................. 40,000

Elongation in 2" (%) ................................3-4

Hardness (Brinell) ................................... 200

• Sizes and Recommended Current Ranges (For flat or down hand positions)

Note: For overhead welding  you have to reduce 5-15 amps and for vertical welding you have to reduce 10-20 amps.

02. 55% NICKEL RODS Specification (AWS/SFA 5.15 Class ENiFe-Cl):

Nickel 55 designed with 55% nickel and 45% iron, which allows to produces of weld deposits and lower weld shrinkage stress. As a result, it reduces the possibility of weld cracking.

This 55% Nickel electrode specially designed to weld heavy sections such as motor blocks, housings, machine parts, frames, etc. This is one of the cheapest options for welding cast iron surface.

• Typical Weld Metal Chemistry (%)

1) C -->1.500, 2) Si --> 0.500, 3) Mn --> 0.300, 4) P --> 0.005,

5) S --> 0.002, 6) Ni --> 53.000, 7) Fe --> Balance

• Typical Mechanical Properties of Weld Metal (As Welded) 

Tensile strength (psi) .......................... 80,000

Yield strength (psi)............................... 60,000

Elongation in 2" (%) ................................6-12

Hardness (Brinell) .................................... 300

• Sizes and Recommended Current Ranges (For flat or down hand positions)

Note: For overhead welding  you have to reduce 5-15 amps and for vertical welding you have to reduce 10-20 amps.

03. Steel Electrode Specification (AWS/SFA 5.15 EST):

Steel Electrode is the most economical electrode for welding cast iron. It comes with a low melting temperature, which allows operating welding machines at low welding current. Since the core wire is made of steel, the welding tensile strength is higher than 99% NICKEL RODS.

• Typical Weld Metal Chemistry (%)
  

1) C --> 0.950, 2) Si --> 0.640, 3) Mn --> 0.450, 

4) P --> 0.018, 5) S --> 0.008, 6) Fe --> Balance

• Typical Mechanical Properties of Weld Metal (As Welded)

Tensile strength (psi) .......................... 65,000

Yield strength (psi) .............................. 50,000

Elongation in 2" (%) ..................................... 5

Hardness (Brinell) ............................. 300-330

• Sizes and Recommended Current Ranges (For flat or down hand positions)

Note: For overhead welding  you have to reduce 5-15 amps and for vertical welding you have to reduce 10-20 amps.

What Methods to Use

There are several ways to weld cast iron for satisfactory welds. Generally, ARC, MIG, TIG welding process are compatible. For achieving good welds you have to keep a sharp eye on heat management.

According to heat management and other aspects stick welding technique is more appropriate. That gives you great results with 95 amps on DCEP.

On the other hand, the MIG welding process is the second-best process for welding cast iron. You can also weld cast iron cracks with a TIG welder. But you have to be careful in this process, there is a possibility to mess up.

You can also try gas welding, but the main drawback is cools slowly and the possibility of distortion in the iron for high heat.

Final Verdict

When you decided to work with cast iron, need to collect an appropriate welding rod, that depends on the chemistry of welded material and the specification of the electrode. If you are a newbie, you will have to increase your knowledge and skill of welding. Hopefully, our guideline about cast iron welding rods for developing your knowledge has been helpful in your search.

FAQ

Source:

• https://www.stoodyind.com/Catalogs/FISC/current/05catpg352.pdf
  
• https://www.twi-global.com/technical-knowledge/job-knowledge/weldability-of-materials-cast-irons-025