[Zurück]

M. Vogric, E. Kozeschnik, J. Svoboda, S. Zamberger, E. Povoden-Karadeniz:
"Modelling of grain boundary cementite growth kinetics in hypereutectoid steels by conventional and autocatalytic ledge growth approaches";
Vortrag: EUROMAT 2021, Graz; 13.09.2021 - 17.09.2021.

Hypereutectoid steels are of great use for the cable industry due to their hardness and toughness. However, the formation of a grain boundary proeutectoid cementite phase due to the high carbon concentration has a deleterious effect on the material´s properties. Understanding the growth kinetics of grain boundary cementite is therefore a question of major industrial importance and an unresolved subject of debate since the 1960s´.

We present and compare two different modelling approaches of isothermal grain boundary cementite growth.

The first relies on a conventional diffusion-based nucleation and growth of the cementite phase. This approach led historically to simulation results overestimating the grain boundary cementite thickness in comparison to the experiment. We managed however to improve considerably the fit of experimental data using the precipitation simulation module of MatCalc with adaptations for the grain boundary diffusion geometry and the heterogeneous nucleation site energy.

The second modelling approach also relies on diffusional growth, but takes into account the stepped morphology of the cementite/matrix interphase by linking the grain boundary cementite thickness evolution to the nucleation rate of cementite ledges as a function of time. This approach also leads to a very good fit of experimental data for all tested alloys. It describes the nature of an interfacial structure barrier to ledge formation assumed in the literature using a semi-empirical formulation of the energy barrier to ledge nucleation. We discuss the advantages and limitations of both approaches, and their consequences on the physical understanding of grain boundary cementite growth.

hypereutectoid; steel; cementite; grain boundary; ledge; precipitation; nucleation; growth

https://publik.tuwien.ac.at/files/publik_301547.pdf