Diffusion-controlled growth of pearlite in ternary steels

A theory for the diffusion-controlled growth of pearlite in steels containing manganese is presented and assessed in the light of experimental data. Given the overwhelmingly rapid diffusivity that a substitutional solute has within the transformation front, the growth rate is found to be dominated by diffusion parallel to the interface with austenite as the rate controlling step. The relevant interfacial diffusion parameters have been derived by fitting experimental data to kinetic theory. All reported measurements of pearlite growth where the full set of necessary parameters have been listed, are shown to be inconsistent with mechanisms that do not involve the partitioning of substitutional solutes. The method adopted here, which is based on the local equilibrium at the transformation interface with the long-range partitioning of substitutional solutes by migration within the interface, has been shown to reasonably explain experimental data over a range of temperatures and chemical compositions.

Mixed diffusion-controlled growth of pearlite in binary steel

A kinetic theory for the diffusion-controlled growth of pearlite is presented, which accounts simultaneously for diffusion through the austenite and via the transformation front. The simplified method abandons the need for mechanical equilibrium at the phase junctions and yet is able to explain experimental data on the growth rate of pearlite. Furthermore, unlike previous analyses, the deduced value for the activation energy for the interfacial diffusion of carbon is found to be realistic when compared with corresponding data for volume diffusion.