| Title |
Effect of Hf and Ce Additions on Microstructure and Mechanical Properties of Direct Energy Deposited Fe-24Mn-4Cr-0.4C High Manganese Steel |
| Authors |
김민기(Minki Kim) ; 박지영(Jiyoung Park) ; 조해주(Haeju Jo) ; (Tomasz Choma) ; (Julia Chmielewska) ; (Christian Leinenbach) ; 이욱진(Wookjin Lee) |
| DOI |
https://doi.org/10.3365/KJMM.2026.64.8.710 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
Additive manufacturing; Grain refinement; L-DED; Micro-alloying; High manganese steel |
| Abstract |
Laser directed energy deposition (L-DED) of high-manganese steel effectively suppresses manganese (Mn) macro-segregation due to its rapid solidification characteristics. However, this process inherently induces a severe thermal gradient along the building direction (BD), resulting in coarse, BD-aligned columnar grains and highly anisotropic mechanical properties. To mitigate these microstructural limitations, minor amounts of hafnium (Hf) or cerium (Ce) were micro-alloyed into a base Fe-24Mn-4Cr-0.4C matrix, and their subsequent effects on the microstructure and tensile behavior along both the BD and transverse direction (TD) were systematically investigated. Both Hf and Ce acted as oxygen getters, forming HfO2 and CeO2 precipitates that reversed the Marangoni flow and produced wider, shallower melt pools, thereby weakening the BD thermal gradient. This structural alteration shortened the BD solidification-cell length, increased the fraction of high-angle grain boundaries, and reduced the (001)//BD cube-like texture. Furthermore, CeO2 promoted heterogeneous nucleation more effectively than HfO2 due to its superior lattice matching with gamma-Fe. Sub-boundary refinement consequently increased the BD yield strength while preserving the TD strength, thereby reducing the anisotropy. Although the BD elongation decreased slightly with Ce addition, it dropped significantly with Hf addition, because the low coherency of the HfO2 interface promoted interfacial decohesion and void nucleation. These findings indicate that Hf and Ce micro-alloying refines the solidification structure and balances strength and ductility, with Ce being the more favorable additive. |