PSI - Issue 81

Pavlo Prysyazhnyuk et al. / Procedia Structural Integrity 81 (2026) 552–557

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The mechanical response of the coatings was evaluated by measuring their hardness in both the as-deposited (before deformation) and strain-hardened (after deformation) states, as a function of the Mo 2 C content in the flux (Fig. 5). In the as-deposited condition, the hardness exhibits a strong, near-linear dependence on the Mo 2 C concentration. Starting from a baseline of approximately 20 HRC for the pure high-manganese steel matrix, the hardness progressively increases to a plateau of about 35 – 37 HRC at 15 – 20 vol.% Mo 2 C. This significant increase is directly attributable to the formation of the hard, wear-resistant (Mo,M) 2 C primary carbide network within the microstructure. The increasing volume fraction of this reinforcing phase effectively enhances the material's resistance to plastic deformation, which is reflected in the higher hardness values. The strain-hardening behaviour of the coatings reveals a more complex trend. For alloys with low Mo 2 C content (0 – 10 vol.%), a notable capacity for strain hardening is observed, with hardness increasing by approximately 5 HRC after deformation. This behaviour is characteristic of the austenitic matrix, which undergoes twinning-induced plasticity (TWIP) effect, a hallmark of high manganese steels. However, as the Mo 2 C content increases beyond 10 vol.%, the strain-hardening response becomes marginal. This suggests that the microstructure becomes dominated by the rigid, non-deformable carbide network. While this network provides excellent initial hardness, it constrains the deformation of the surrounding ductile matrix, thereby suppressing its ability to strain-harden effectively. In conclusion, a clear trade-off exists between the initial hardness and the strain-hardening response of the coatings. The former is directly proportional to the Mo 2 C content, whereas the latter is inversely affected, as the rigid carbide network restricts the plasticity of the austenitic matrix.

Fig. 5. Hardness dependence of the high-manganese steel – Mo₂C system coatings on the carbide phase content in the deformed and undeformed states.

4. Conclusions This study of Mo 2 C-reinforced high-manganese steel coatings demonstrated the formation of a unique microstructure and set of properties. The analysis revealed that the system's solidification follows a eutectic-type reaction; however, for the compositions studied, the primary phase to crystallize from the liquid is the complex carbide, (Mo,Mn,Fe) 2 C. This results in an in-situ composite microstructure where a discontinuous network of hard, angular primary carbides is embedded within a eutectic metallic matrix. This carbide network is directly responsible for the substantial increase in as-deposited hardness from approximately 20 HRC to over 35 HRC. At the same time, this rigid framework was found to limit the alloy's capacity for work hardening. This is attributed to two main factors: the physical constraint of plastic deformation within the matrix by the carbide network and the partitioning of manganese (a key element for strain hardening) into the carbide phase. A significant positive finding is that alloying with molybdenum successfully suppresses the formation of embrittling cementite (Fe 3 C). The resulting coatings, characterized by high initial hardness but limited strain-hardening capacity, are therefore recommended for applications subjected to high static and dynamic contact loads where resistance to initial plastic deformation is the primary requirement. Acknowledgements The authors express their sincere gratitude and respect to the Armed Forces of Ukraine, who made it possible to complete the preparation of this article for publication. The authors also express their gratitude to the Ministry of Science and Education of Ukraine for grants for the implementation of the project 0123U101858. References

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