To control the production processes and design product properties of promising medium and high-Mn steels, reliable solidification and material models are essential. High precision and experimentally validated thermodynamic data are essential data sources for all these models. As manganese is a segregating element, it is crucial to describe high manganese concentrations well, e.g. for the final stage of solidification.
Especially regarding higher manganese content, there is a remarkable lack of experimental data. All of the thermodynamic Calphad descriptions published by [Huang, 1990], [Djurovic 2011] and [Kim 2015] refer to the solid-liquid transformations exclusively on the measurement data from [Schürmann 1977].
No other data/publications are available, and even [Schürmann 1977] only rarely measured the temperatures of high-Mn steels.
As the above-mentioned thermodynamic descriptions show significant uncertainties at higher Mn content, an own data set of reliable data is necessary for the evaluation, selection, and - if required - for the assessment of the Calphad models. For this purpose, an own experimental study was performed,
and model alloys with Fe-Mn (up to 30 w.t.-% Mn), Fe – 10%Mn – C (up to 2.5 w.t.-% C) and Fe – 20%Mn – C (up to 2.5 w.t.-% C) were produced by induction melting and subsequent centrifugal spin casting. Since manganese has a strong tendency to evaporate when it melts and can quickly destroy measuring devices, a new measuring method was developed. Using a micro-DTA-protected setup with closed crucible by tantalum lids (local-getter and Mn “catcher”), all high-temperature phase transformations (TLiquid, TPeritectic, TSolid, TEutectic, TGamma-Delta) can be measured in equilibrium conditions.
Based on these new experimental results, the thermodynamic description of [Djurovic 2011] is identified as the most accurate one. Nevertheless, there are still considerable deviations with Mn content above 10 w.t.-% and further research is necessary and ongoing.