On the plasticity of MnS at elevated temperatures and its influence on damage prevalence

Forming-induced damage strongly influences the service life and mechanical properties of components made from 16MnCrS5 steel. This damage is initiated in the vicinity of MnS inclusions, which fracture or delaminate at their interfaces due to the mechanical contrast to the steel matrix. Forming processes are often conducted at elevated temperatures; however, the plasticity of MnS at these temperatures in correlation with crystallographic orientation have not been fully explored. In this study, we aim to uncover the high-temperature properties of MnS using micropillar compression and TEM analysis. We then relate them to damage prevalence observed in steel at elevated temperatures with high resolution SEM imaging in combination with AI-assisted damage analysis. We demonstrate that the mechanical contrast of MnS and steel influences the damage prevalence significantly showing a minimum at 400 °C. We additionally determine the CRSS for the primary $\left\{110\right\}$ $〈1\overline{1}0〉$ slip system in the temperature range from 20 °C to 600 °C and the CRSS for the secondary $\left\{111\right\}$ $〈1\overline{1}0〉$ slip system at temperatures of 400 °C and 600 °C. We show that MnS exhibits a yield strength anomaly at 400 °C in specific orientations and at slow loading rates that is accompanied by a change of the active slip system. We relate this yield strength anomaly to thermally activated cross-slip and increased impurity mobility at elevated temperatures.