is the maximum diameter of round bar at the centre of
which the specified properties may be obtained. Table 12.2 shows an example.
The reason for the difference of mechanical properties for different size bars
of the same steel is that during the heat treatment different rates of cooling
occur at the centres of such bars due to their differences in sizes (see Figure
12.15).
This results in differences in micros true ture and hence differences in
mechanical properties.
12.5 Tempering
Martensite is a hard and brittle substance. Thus a steel which has been
quenched so that its entire microstructur ...
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