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 slowly in the furnace
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 below or closes to the lower critical temperature and then cooled slowly

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Engineering Materials
The unit cells

Have the same orientation and their similar faces are parallel
May be defined as the smallest parallelepiped which could be transposed in three coordinate directions to build up the space lattice
All of these
Contain the smallest number of atoms which when taken together have all the properties of the crystals of the particular metal

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