Engineering Materials
When low carbon steel is heated up to lower critical temperature

The grain size first increases and then decreases very rapidly
The average grain size is a minimum
There is no change in grain size
The grain size increases very rapidly

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

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

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