On the Competitive Substitutional Partitioning During Nano-pearlitic Transformation in Multicomponent Steels

Bulk nano-pearlitic microstructure with apparent interlamellar spacing below 100 nm has been attained by rapidly undercooling a hypereutectoid multicomponent steel below equilibrium eutectoid temperature from the austenitization temperature. The aforementioned processing rendered non-partitioned pearlite growth in the steel, as confirmed by acquiring compositional variation across the austenite/pearlite growth front using scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDS) technique. The post transformation sidewise partitioning of substitutional components between ferrite and cementite has been critically assessed by interrupting the cooling process at various intervals followed by STEM-EDS and atom probe tomography (APT) across the austenite/pearlite and ferrite/cementite interfaces. This partitioning phenomena has been simulated using DICTRA(R) and validated with experimental observations. It is inferred that partitioning kinetics of Mn is fastest in the early stages followed by Cr in the intermediate. However, towards the completion stages of partitioning, Mn and Si have much faster rate as compared to Cr.