COARSENING KINETICS OF Fe3C PARTICLES IN Fe-0.67 %C STEEL

Kinetics of Fe(3)C particle coarsening in Fe-0.67%C steel for of two materials (A, B) of different microstructures (with different matrix (ferrite) grain size and particles distribution) was investigated. In material A, obtained by quench-hardening with subsequent tempering, the particles are mainly at grain (subgrain) boundaries of fine-grained matrix formed by in situ recrystallization of ferrite. In material B, obtained by recrystallization after cold rolling (10%), particles are mainly inside grains of coarse-grained matrix formed by discontinuous recrystallization of ferrite. During annealing (at 680, 700 i 715 degrees C up to 800 hours) the microstructure morphology of A and B is preserved; the material microstructure determines the particle coarsening rate, it is lower in B. Analysis of empirical kinetic functions with the LSW theory suggest that higher particle coarsening rate in A results from higher diffusivity of Fe along the matrix grain boundaries. Lower particle coarsening rate in B results from matrix diffusion of C and Fe.