PARTITIONING OF SILICON DURING PEARLITE GROWTH IN A EUTECTOID STEEL

The partitioning of silicon between ferrite and cementite lamellae at the reaction front during the austentite-pearlite transformation has been studied in a 2% silicon eutectoid steel, using analytical electron microscopy. To overcome the fineness of the lamellar structure, analyses were made on cementite plates extracted on carbon replicas, and these showed that silicon partitioned preferentially to ferrite at the reaction front for temperatures in the range 600-750°C. Although the extent of partitioning at the front decreased with undercooling, there was no well-defined no-partition temperature. Calculations supported the view that the partitioning observed was kinetically feasible. At reaction temperatures where partitioning at the transformation front was not complete, further rapid segregation of silicon occurred behind the front so that, within about one minute, near to equilibrium partitioning was achieved. Calculations showed that the segregation observed behind the front could occur by volume diffusion of silicon, and that silicon diffusivity at 650°C was only slightly lower in cementite than in ferrite. © 1979.