Cast Iron
The term cast iron covers a range of important specialised engineering materials with differing properties and intended for various applications. The main types of cast iron are Grey, White, Malleable and Alloy. Grey cast iron contains 2 to 4%C and over 2%Si. It is fairly soft and not as brittle as white cast iron and is used for general iron castings. White cast iron may have the same range of carbon as grey but has less than 1%Si. It is much harder and more brittle than grey, and is used in applications where abrasion is likely to occur. Malleable cast irons are basically heat-treated white cast iron. There are two main types, white heart and black heart, so called because of the distinctive appearance of their fracture surfaces. Alloy cast irons may be alloyed with chromium, nickel, molybdenum, and other elements to give specific strength, corrosion, or high temperature properties. Welding cast iron is always difficult due to their inherent low ductility, presence of brittle constituents, formation of carbides, and possible variations in section. White cast iron and some alloy cast irons are virtually unweldable, and malleable cast irons can be very difficult. Grey cast iron may be welded by preheating to red heat, or alternatively welded cold and keeping heat input very low. Specialised consumables are available for MMA, TIG, FCAW, and gas welding.
|
