Cast Iron

The usual rule in welding, “to select the filler materials according to the chemical composition and mechanical properties of the base materials to be welded”, does not apply for the welding of cast iron.

As all kinds of cast iron have one thing in common, a carbon content of between 3% to 4%, welding with filler materials of similar high C-content is only possible with preheating up to 600°C and post-heat treatment for several hours. This is called the “cast iron hot welding process”, which is carried out on special applications where colour matching and mechanical machineability are of great importance.

For about 95% of all cast iron welding applications: nickel-, nickel-ferrum- or nickel-copper-alloyed welding electrodes are used very successfully. These electrodes are suitable for all kinds of cast iron welding applications and normally no preheating or post-heating is required. This is called the “cast iron cold-welding process”.

Although several grades of cast iron are in practical use, normally only grey cast iron (like FC18, FC20, FC25, etc) needs repair welding. In case welding is required for construction purposes, PACWELD 213 alloyed electrodes are most suitable. Modular cast iron (like CD40, FCD45 etc) seldom breaks and white cast iron, chilled cast iron, wear and heat corrosion resistant cast irons and special castings are rare welding applications where special welding procedures are required. Please ask your PACWELD representative for advice.

How to select the most suitable electrode for welding depends not only on the kind of cast iron to be welded but also other important factors to be considered are:

  1. Risk of cracks due to heat input during welding
  2. Machineability of weld deposit and heat affected zone
  3. Conditions of the cast iron application; e.g. contaminated with oil, oxidised and burnt due to high operation temperatures
  4. Size of application (multi-layers, preheating, etc) free to contract during welding (peening required or not)
  5. Casting quality (impurities, etc)

Electrode specifications according to DIN, AWS-ASME, JIS, BS etc are no proof of quality. The quality of cast iron welding electrodes is related very little to the alloy it is made of (Ni, NiFe or NiCu). However, this is the only information you get from specifications like (e.g. AWS E-Ni, E-NiFe, E-NiCu, etc).

The quality in cast iron electrodes is based on the following factors:

  1. How good is the ability of the electrode to absorb surface impurities like oil, grease, paint, etc, during welding without forming blowholes or pores?
  2. How good is the penetration in heavily contaminated or burnt cast iron without creating undercuts?
  3. How easily machineable is the heat affected weld zone between weld deposit and base material?
  4. How good is the weldability on DC and AC, in downhand or position welding, on clean or dirty surfaces, etc?
  5. How much does the NiFe electrode overheat particularly on AC) during welding, causing waste of long stubs?
  6. How good is the crack resistance (elongation/ductility) of the weld deposit in multi-layer applications?
  7. How well is the carbon distribution to avoid discolouration and differences in hardness within multi-layer weld deposits which influence heavily the weld deposit’s machineability?

All of the above factors depend totally on the quality of the coating the electrode is made of and not on the type of alloy. The particulars of the coating formula for cast iron electrodes however is the “know-how” of each individual electrode maker and will not be released for standardisation in specifications.

PACWELD offers the most up-to-date range of cast iron electrodes for all kinds of cast iron welding applications and for all conditions common in practical cast iron welding. Do not rely on specifications when it comes to cast iron welding.