If a quenched carbon steel is overtempered the Fe3C particle

If a quenched carbon steel is overtempered, the Fe_3C particles coarsen (they get larger, further apart, and fewer in number). What is the driving force for this process?

Solution

when a steel is over tempered grain growth takes places . the grains gets larger and bigger in shape. the reason or driving force behind this is that when the steel is over tempered it is heated at a temperature about 600-700 degree celcius ehich is almost equal to the recrystallization temp of steel and hence because of the heat supplied the grains gets energy and starts expanding which results in larger grains .