Pearlite Growth Kinetics in Fe-C-Mn Eutectoid Steels: Quantitative Evaluation of Energy Dissipation at Pearlite Growth Front Via Experimental Approaches

Essential understanding of the pearlite growth kinetics is of great significance to predict the lamellar spacing and the resultant mechanical properties of pearlitic steels. In this study, a series of eutectoid steels with Mn addition up to 2 mass pct were isothermally transformed at various temperatures from 873 K to 973 K to clarify the pearlite growth kinetics and the underlying thermodynamics at its growth front. The microscopic observation indicates the acceleration in pearlite growth rate and refinement in lamellar spacing by decreasing the transformation temperature or the amount of Mn addition. After analyzing the solute distribution at pearlite growth front via three-dimensional atom probe, no macroscopic Mn partitioning across pearlite/austenite interface is detected, whereas Mn segregation is only observed at ferrite/austenite interface. Furthermore, in-situ neutron diffraction measurements performed at elevated temperatures reveal that the magnitude of elastic strain generated during pearlite transformation is very small. Based on the thermodynamic model, these experimental results are used to estimate the contribution of various factors to the total energy dissipation. Compared with the Mn-free alloy, the retardation effect of Mn addition on pearlite growth kinetics, which is partly due to the reduced driving force for pearlite growth, can be well explained by further considering the solute drag effect of Mn.