Ferrite-Cementite Interface

written by Jaemin Kim ( jaeminkim88@kaist.ac.kr )

Even though the pearlitic steel is the primary engineering materials because of its highest

strength and good ductility, it has been ambiguously studied the origin of mechanical

properties of pearlitic steel and the mechanisms of pearlitic transformation. To reveal the

secret of mechanical properties and pearlitic transformation, we have carried out the detailed

inspection on the structure of ferrite/cementite interface assuming pearlite are equivalent with

a ferrite/cementite bilayer.

To achieve our goal, it is necessary to analyze the misfit dislocation at ferrite/cementite

interface in quantitative manner. So we combine the atomic simulation with atomically-

informed Frank-Bilby (AIFB) method. The analysis results gives typical semi-coherent

interface and detailed information of misfit dislocation. The misfit dislocation can act as

sources, sinks, barriers and storage site for vacancy, interstitial and dislocation. As a results,

the interface structure have a strong influence on plastic deformation of metal. In other

words, the mechanical properties of pearlitic steel are highly dependent with the misfit

dislocation of ferrite/cementite interface. On the other hands, pearlitic transformation

involves not only diffusional process, but also migration of heterophase boundary. In general,

semi-coherent boundary like a ferrite/cementite interface can migrate by ledge mechanism

with low energy barrier because introducing the misfit dislocation reduces the strain energy

of the overall system. So it accelerates the formation of pearlite colony in the

thermodynamics point of view.