When steels with more or less carbon than the eutectoid composition are cooled slowly or held isothermally below the eutectoid temperature, the appearance of the pearlite is usually preceded by the precipitation of proeutectoid cementite and ferrite, respectively, at the grain boundaries prior to the eutectoid reaction [1]. For austenite being cooled well below the eutectoid temperature, for example, at the bainite formation region in a time–temperature–transformation (TTT) diagram