Effects of annealing temperature on cellular structure and mechanical properties of additively manufactured 304L stainless steel by directed energy deposition

The mechanical properties of additively manufactured 304L stainless steel are strongly influenced by cellular structures, which include high dislocation densities, low-angle grain boundaries, and elemental segregation. To investigate the impact of these features on material strength, the as-built 304L stainless steel was subjected to annealing treatments at temperatures ranging from 750 °C to 1150 °C. The microstructural changes within the cellular structures after annealing were analyzed using electron microscopy techniques. The contributions of each microstructural feature to the yield strength were quantitatively assessed and compared with the yield strengths obtained from tensile testing. It demonstrates that elemental segregation and dislocation density on the cellular structures are the dominant factors governing the high yield strength of additively manufactured 304L stainless steel. In addition, it was confirmed that elemental segregation in the cellular structure can affect the martensitic transformation under tensile deformation, which may affect the strain induced plasticity (TRIP) effect.