Spatial Distribution of Cementite Particles in Fe-0.67% C Steel

Abstract

The particles arrangement in material space is represented by point field determined by the particle reference points, i.e., particle centers which can be described by the pair-correlation function (PCF) g3(r); r - correlation distance. Information about g3(r) can be obtained by stereological method based on the PCF g2(r), which describes the point field on the planar section determined by the centers of particle planar sections. In this paper the arrangement of cementite (Fe3C) particles during coarsening in Fe - 0,67%C steel at 715ºC in a form of two materials (A, B) of different microstructure of the coarse spheroidite (with different matrix grain size and particles position) was investigated. In material A, the particles are mainly at grain (subgrain) boundaries of fine-grained matrix. In material B, particles are mainly inside grains of coarse-grained ferrite. For material A, the empirical PCF g2(r) for a long time of coarsening (600 hours) is shifted towards larger r and is more flat near the g2(r) =1 than the one of coarsening for 50 hours. For material B, the g2(r) for both annealing times are not significantly different. This is consistent with the results of the probability density function f2(d) analysis for diameter (d) of the particle sections. Obtained PCF g2(r) are similar to the PCF g2(r) for planar section of the Stienen model. This means that for both type of microstructures the PCF - g3(r) =1, i.e., particles are distributed randomly in space and the sizes of the neighboring particles are correlated with each other.