Question

Cite how the cooling rates affect the formation of the lamella in eutectoid, hypoeutectoid, and hypereutectoid microstructures.

Answer 1

Cooling rate indirectly affected by the composition of the carbon present in the alloy.

If hardenability is high incubation period is more for the formation of perlite.

With same cooling rate given to these three types

Hypereutectoid forms very early

Later hypoeutectoid and finally eutectoid forms the pearlite.

In hypo and hyper cases already proeutecoid phases forms above eutecoid tempratures so that will act as a nucleating sites for pearlite formation .

But in eutectoid case both phases have to be simultaneously nucleates on the austenite grain boundaries.

So that cooling rate affect the Microstructure based on the composition of the alloy.