Why is it difficult to weld cast iron?

Cast iron is difficult, but not impossible, to weld. In most cases, welding on cast iron involves repairs to castings, not joining casting to other members. A few facts about cast iron help in understanding the welding challenges. Cast iron typically has a carbon content of2% -4%, roughly10 times as much as most steels. The high carbon content causes the carbon to form flakes of graphite. This graphite gives gray cast iron its characteristic appearance when fractured. A critical temperature in most cast iron is about1450 degrees F. When at this temperature, conditions that can lead to cracking occur. While the arc will heat the casting to temperatures above this level, it is important that the casting not be held at this temperature for long periods of time.Proper selection of welding electrodes and pre heating the cast iron before welding will help reduce the possiblilty of cracking.

Carbon Percentage in cast iron is High which make it brittle. So during the welding, coz of stress and heat it is prone to cracking.

cast iron has high content of carbon from2-4% and increasing carbon percentage decrease weldability

welding cast iron need high careful with suitabe series of heat treatment

mainly because during the welding process cast iron; being brittle, is prone to cracking. ways to prevents this are to preheat the whole piece to cherry red and when completed allow it to slow cool by wrapping in rock wool.

due to the brittle nature of most cast iron

due to high carbon content in CS its difficult to perform welding on CS materials since welding will eventually lead to formation of cracks because of stress generated.

It is difficult to weld cast iron if you dont know the procedure of doing it and if you dont know the proper electrode to be use.

the repair are mainly came from forging ,so that is not difficult to weld, some air gap will occur so porosity will comes during welding

Cast iron is difficult to weld because it need an expert to handle the welding, the electrod takes time  .

yes its difficult, but possible 

Any Material Have High Carbon Content Is There  Will Produce Crack After 48 or 72 Hours.