The remaining austenite then transforms to pearlite as the sample is cooled further, however the proeutectoid ferrite is stable and remains in the final polycrystalline material. This is illustrated ...

The microstructure is now a ploycrystalline pearlite with the hard-brittle proeutectoid cementite on the grain boundaries. This structure makes the alloy more brittle than the eutectoid pearlite ...