Final answer:
White cast iron is considered un-weldable due to its hardness and brittleness caused by high carbon content and carbide impurities. Other types of cast iron, like gray and malleable cast iron, are more weldable.
Step-by-step explanation:
There are different types of cast iron, and some types can be more difficult to weld than others. One type of cast iron that is generally considered un-weldable is called white cast iron. White cast iron is characterized by its hardness and brittleness, which makes it challenging to join using conventional welding techniques.
White cast iron contains carbide impurities that contribute to its hardness but also make it susceptible to cracking during the welding process. The high carbon content and cooling rates during solidification can lead to the formation of brittle martensite, which further affects the weldability of white cast iron.
In contrast, other types of cast iron, such as gray cast iron and malleable cast iron, are more weldable due to their lower carbon content and different microstructures.