Engineering Materials
In a hardening process, the hypo-eutectoid steel is

Heated from 30°C to 50°C above the upper critical temperature and then cooled suddenly in a suitable cooling medium
Heated from 30°C to 50°C above the upper critical temperature and then cooled in still air
Heated from 30°C to 50°C above the upper critical temperature and then cooled slowly in the furnace
Heated below or closes to the lower critical temperature and then cooled slowly

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Engineering Materials
Duralumin contains

4 to 4.5% magnesium, 3 to 4% copper and rest aluminium
3.5 to 4.5% copper, 1.2 to 1.7% manganese, 1.8 to 2.3% nickel, 0.6% each of silicon, magnesium and iron, and rest aluminium
3.5 to 4.5% copper, 0.4 to 0.7% magnesium, 0.4 to 0.7% manganese and rest aluminium
5 to 6% tin, 2 to 3% copper and rest aluminium

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Engineering Materials
Ductile cast iron

Is also known as chilled cast iron and is obtained by cooling rapidly. It is almost unmachinable
Contains 1.7 to 3.5% carbon in Free State and is obtained by the slow cooling of molten cast iron
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
Is produced by annealing process. It is soft, tough and easily machined metal

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