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What are the different types of cast iron which can be welded?

Frequently Asked Questions

  1. Grey or flake graphite CI - where the graphite exists as branched interconnected flakes; this type of iron is relatively cheap and has poor mechanical properties. Grey irons are usually weldable with MMA (SMA), MIG (GMA) or FCAW, provided special consumables and procedures are used.
  2. Nodular or spheroidal graphite CI (ductile iron) - where the graphite exists as graphite in a spheroidal form and the mechanical properties approach those of steel. Nodular irons are generally easier to weld than grey irons, but still require special consumables and procedures.
  3. Malleable CI - where the graphite exists as nodules or rosettes produced by heat treatment. Malleable irons have two main forms: blackheart malleable, which has similar weldability to nodular cast iron, and whiteheart malleable, which is readily weldable with ferritic consumables provided care is taken to limit penetration.
  4. White CI - A hard, brittle iron containing no free graphite. White irons are generally considered unweldable.
  5. Austenitic CI - where the graphite may exist in either flake or nodular form, resulting in good corrosion and heat resistance. Many grades of austenitic irons can be welded with special consumables and procedures.
  6. A cast iron with high silicon and aluminium contents where the graphite exists mainly as flakes and the material has good corrosion resistance. This alloy can be welded with special consumables and procedures.
All cast iron welding requires care. If in doubt, contact an experienced practitioner.

Further information is available in:

Welding of cast irons - a guide to best practice

C.L.M.Cottrell, 'Welding cast irons', published by TWI, Abington, Cambridge, UK, 1986 and available from Woodhead Publishing, Abington, Cambridge, UK. e-mail: sales@woodhead-publishing.com
ISBN 0 85300 176 6