KINETICS OF AUSTENITIC ISOTHERMAL DECOMPOSITION AND Mn PARTITION IN Fe-C-Mn-B ALLOYS

A proper addition of Mn to Fe-C alloys could delay the isothermal transformation andchange remarkably the TTT-curves to bay-like shape.The concentration of Mn at the α/γinterphase boundary and thir partition between α- and γ- phase were measured bySTEM/TEM-EDAX.The results show that the partition of Mn diminishes gradually asthe reaction temperature decreases.There exists a certain temperature range with the strong-est Mn concentration spike at the interphase although no Mn partition is found betweenaustenite and ferrite,and this temperature range is correspondent with the bay-temperatureon TTT curves of the alloys.It is thus suggests that the change of TTT-curve configuration isdue to the partition of alloy elements.The bay-like shape is attributed to the solute drag ef-fect and the solute drag-like effect caused by the enrichment of Mn at the α/γ interphase.