Cast iron is an
iron-based material with a high percentage of carbon. The five types of cast iron are
gray, white, malleable, alloy, and nodular.
Gray cast iron is
used a great deal for machine castings. It can readily be identified by the dark gray,
porous structure when the piece is fractured. Gray cast iron can be welded with
comparative ease.
White cast iron
possesses what is known as combined carbon. The fractured piece of white cast iron
will disclose a fine, silvery white, silky, crystalline formation. Although white cast
iron can be welded, welding is not recommended for this metal.
Malleable cast iron
is usually white cast iron which has been subjected to a long annealing process. A
fractured piece of malleable cast iron will indicate a white rim and a dark center.
Malleable cast iron can be welded; however you must be sure that the metal is not heated
above critical temperature. Heating beyond this point reverts the metal back to its
original characteristics of white cast iron.
Alloy cast iron
can be arc welded, but greater precautions must be taken in the preheating and post-weld
heat treatment to prevent the destruction of the alloying elements.
Nodular iron
sometimes called ductile iron has the ductility of malleable iron, the corrosion
resistance of alloy cast iron and tensile strength greater than gray cast iron. Nodular
can be arc welded, providing adequate preheat and post-weld heat treatments are used;
otherwise some of the original properties are lost.
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| Gray iron
castings |
...Grade 20, 25, 30,
35, 40, 45, 50, 55, 60 |
| Ductile
iron castings |
...Grade 60-40-18, 60-45-12, 80-55-06,100-70-03,
120-90-02, 80-60-03 |
| White
iron castings |
...Most grades |
| Austempered
ducitle iron castings |
...Grade 1, 2, 3, 4, 5,
6 |
| Ni-resist iron
castings |
...Type 1, 1b, 2, 2b,
3, 4, 5, 6 |
|