Grain refinement of high-Mn wear-resistant cast steel by means of heterogeneous nucleation

Understanding and controlling the primary solidification, particularly
the formation of first grains, is of significant relevance. Generally, high-Mn steels,
such as alloy Mn13, exhibit a coarse-grained microstructure in the millimeter
range and are known for their high strain hardening ability and thus, excellent
cyclic deformation resistance. To further improve the cyclic mechanical
properties, this study aims to increase the strength of the alloy via grain
refinement. From a comprehensive literature research, the nonmetallic
inclusions AlCeO3, CeO2, Ce2O3 and Ce2O2S were identified as the most promising particles for the heterogeneous nucleation of austenite. Based on this literature review, various grain refining agents were evaluated and finally the grain refining agent from ELKEM (WearSeedTM) was selected for test melts. This resulted in a successful grain refinement and the grain size was reduced by over 80% (from 1550μm to 285μm). However, the process window for a successful grain refinement is only very small. For a deeper understanding, thermodynamic
calculations with FactSage on the interaction of O-S-Ce-Al in high-Mn steel melts
and particle analyses of the potential nuclei by automated SEM-EDS were carried
out. The framework conditions for a successful grain refinement were
systematically developed depending on the casting temperature, dissolved O and S, and the addition of Al and Ce. Finally, the static and cyclic mechanical
properties of the grain refined high-Mn steel cast were determined using tensile
and low cycle fatigue testing and showed very promising results.