A revisited Johnson-Mehl-Avrami-Kolmogorov model and the evolution of grain-size distributions in steel

TL;DR

This paper revisits the Johnson-Mehl-Avrami-Kolmogorov model to better understand ferrite grain growth in steels, developing a Fokker-Planck law for grain size distribution and proposing a method to compare theoretical and experimental data.

Contribution

It introduces a Fokker-Planck evolution law for grain size distribution in steels, extending classical nucleation and growth models with a new analytical approach.

Findings

The grain size distribution follows a log-normal distribution.

Numerical studies confirm the model's qualitative behavior.

A strategy for comparing theoretical and experimental distributions is proposed.

Abstract

The classical Johnson-Mehl-Avrami-Kolmogorov approach for nucleation and growth models of diffusive phase transitions is revisited and applied to model the growth of ferrite in multiphase steels. For the prediction of mechanical properties of such steels, a deeper knowledge of the grain structure is essential. To this end, a Fokker-Planck evolution law for the volume distribution of ferrite grains is developed and shown to exhibit a log-normally distributed solution. Numerical parameter studies are given and confirm expected properties qualitatively. As a preparation for future work on parameter identification, a strategy is presented for the comparison of volume distributions with area distributions experimentally gained from polished micrograph sections.