ALLOY CAST IRONS
Introduction:-
To over come some inherent difficulties in ordinary cast iron and to give qualities more suitable for special purpose, while retaining the important castings advantages of its metals, a large number of alloy cast iron have been developed. When alloying elements are added to cast iron, certain characteristics are obtained more uniform structure, better hardness, wear resistance, strength and machinability. Also the other properties such as thermal expansion, thermal conductivity, magnetic and electric properties can be adjusted. Alloy cast irons those to which alloying additions are intentionally made to impart particular property. E.g. for alloy cast iron are
- Nickel Cast iron
- Nickel hard white cast iron.
Nickel cast iron:-
Nickel acts as graphitizer and improves machinability. Nickel with silicon adjusted, acts as densner giving a fine grain size. Properties will be more uniform. Progressive increase in nickel content changes the microstructure from pearlite to martensite and to austenite. By addition of nickel 1.5 to 2% and molybdenum 0.3-0.6% the matrix of cast iron can have a acicular or needle like structure instead of pearlite. This produces a heavy-duty cast iron characterized by heavy sections and good wear resistance. Typical applications are die blocks for pressing or forging and rolling mill rolls.
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