Effect of Hf and Ce Additions on Microstructure and Mechanical Properties of Direct Energy Deposited High Manganese Steel

Additive manufacturing (AM) is a layer-by-layer fabrication method that enables the manufacturing of components of complex 3D shapes while minimizing material waste. Among various AM techniques, Laser Direct Energy Deposition (L-DED) is a metal additive manufacturing process in which metal powder and a high-energy laser are simultaneously delivered to form a deposited structure. On the other hand, High-manganese steels (HMnS) are known for their excellent tensile strength, ductility, and high work-hardening capability. However, their high Mn content leads to segregation during casting, thereby reducing hot workability. The rapid cooling rates associated with the L-DED process have been reported to mitigate segregation issues, making it a promising approach for processing HMnS. Recently, it was shown that HMnS could be successfully fabricated by L-DED process. Although near defect-free alloy could be fabricated, the as-deposited alloys exhibited coarser grain sizes compared to conventionally processed HMnS steels which was produced by rolling, resulting in relatively low yield strength and elongation. On the other hand, hafnium (Hf) and cerium (Ce) are commonly known as grain refinement elements in cast steel and iron due to their ability to form fine oxides that can act as nucleation sites. In this study, Fe-10Hf and Fe-10Ce (wt.%) powders were mixed with Fe-24Mn-4Cr-0.4C (wt.%) base powder at a ratio of 99.5:0.5 to achieve target compositions of Fe-24Mn-4Cr-0.4C-0.05Hf and Fe-24Mn-4Cr-0.4C-0.05Ce (wt.%) in the final L-DED processed alloys. Using these mixed powders, L-DED was carried out and the resulted alloys were examined to assess the influence of Hf and Ce additions on the microstructure and mechanical properties of the high-manganese steel produced by the L-DED.