Activation energy for H desorption from simple MnS and MnS–TiN complex inclusions in martensitic medium Mn steels

In this study, we measured the activation energy (E_H) for hydrogen (H) desorption from simple elongated MnS inclusions and fine globular MnS–TiN complex inclusions in medium Mn steels, which possess fully martensitic microstructures and nearly identical chemical compositions. The E_H values were 48.5 kJ/mol for MnS inclusions and 44.7 kJ/mol for MnS–TiN complex inclusions, indicating that the E_H value is not significantly influenced by the type and shape of inclusions. Such similarity arises because the shells of MnS–TiN complex inclusions which surround TiN cores consist of MnS. This suggests that H atoms are not trapped within the inclusions but at the interfaces between the steel matrix and the inclusions. However, the E_H value, even for simple MnS inclusions, can vary with changes in the saddle point energy (E_s) value, reflecting differences in microstructural features and chemical compositions of the steels.