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Weldability of cast iron

Suitability of cast iron for welding

  1. Previous service conditions
    Cast iron that has been exposed to lubricants, superheated steam or aggressive chemicals can become more difficult to weld:
    There is tendency to form porosity in the weld metal or incomplete fusion between the weld metal and the base metal.
  2. Brittleness of cast iron welds
    In grey cast iron and spheroidal graphite cast iron, shrinkage stresses can often exceed the tensile strength. In this case, cracks or breaks will occur.
    The risk of cracking increases with the presence of structural defects such as casting porosity.
  3. Brittleness of grey cast iron
    The brittleness of grey cast iron is due to the presence of lamellar graphite in its structure:
    Local stresses induced by preheating, welding and cooling are concentrated by the graphite flakes.

Design of the weld

  1. The shape of the workpiece
    The shape of the workpiece has an influence on the temperature distribution during welding causing expansion / contraction forces.
    The risk of cracking increases with the complexity of the shape and presence of stress raisers.
    The quenching effect on the weld and HAZ increases with the workpiece thickness and raises the risk of cracking.
  2. Rigid workpiece
    During welding, rigid workpiece cannot move freely. In grey cast iron and spheroidal graphite cast iron, accumulated stresses can even exceed the tensile strength.
    In this case, cracks or breaks will occur.
  3. Free moving workpiece
    Free moving workpieces have a positive influence on weldability.

Welding process and procedure: Arc welding processes

The heat-affected zone (HAZ) is hard and brittle because of the formation of a mixture of iron carbide and martensite - in contrast to the relatively soft structure of cast iron. Contraction induced stresses can accumulate in the HAZ and, subsequently, lead to microcracks.

Safety: Arc welding

see chapter safety

For further information, on-site training, technical advise or project management, please do not hesitate to contact us.

Last update: September 7, 2015

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