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Problems associated with welding cast Irons:

1) Cast iron is that the metal is filled with impurities. When you melt the metal the embedded dirt and sand
contaminated the weld and tend to not mix well with the cast iron filler rod.What you end up with is not a
fused intermixed metal bead but a porosity filled weld that can be easy to chip away with a chisel because it
has not bonded to the base metal. 
2) Pre heat & Post Heat required.And different as per its composition.Pre heat to stress relieve & post heat
to control rate of cooling. 
3) The large amount of carbon in the base metal tends to segregate itself along grain boundaries as the weld
puddle solidifies and cools. What this does is lower the tensile strength even lower so that in the weld fusion
boundary the shrinkage force pulls the metal apart as it cools, ie it tends to crack along the weld when cools. 
4) Cracking. If it cools down too quickly you will get cracks along the weld. 
5) Proper selection of filler rod & flux required as per the grade and composition of the cast iron. 
6) To improve weld performance can be achieved by application of several special techniques. These include:
Joint design modifications. Groove face grooving Studding. Peening. Special deposition sequences and
electrode manipulation. 
7) Some cast irons can not be fusion welded. 
8) Some Cast irons can not be effectively welded.( white Cast Iron)
9) Some Cast iron you shall have to utilize special Ni coated Electrodes. 
10) When welding a large casting expansion and contraction of the casting should be allowed for , maybe
removal/ loosening of foundation etc could be required,


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