Engineering Materials
A material is known as allotropic or polymorphic if it

Exists in several crystal forms at different temperatures
Has a fixed structure under all conditions
Has its atoms distributed in a random pattern
Responds to heat treatment

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Engineering Materials
Ductile cast iron

Is produced by annealing process. It is soft, tough and easily machined metal
Is also known as chilled cast iron and is obtained by cooling rapidly. It is almost unmachinable
Is produced by small additions of magnesium (or creium) in the ladle. Graphite is in nodular or spheroidal form and is well dispersed throughout the material
Contains 1.7 to 3.5% carbon in Free State and is obtained by the slow cooling of molten cast iron

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Engineering Materials
Nickel in steel

Refines grain size and produces less tendency to carburisation, improves corrosion and heat resistant properties
Gives ductility, toughness, tensile strength and anti-corrosion properties
Improves cutting ability and reduces hardenability
Improves wear resistance, cutting ability and toughness

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