Controlling grain structure in metal additive manufacturing (AM) is critical for mitigating anisotropic mechanical behavior caused by columnar grain growth along the build direction. Grain refinement not only reduces hot cracking susceptibility but also enhances mechanical performance via the Hall–Petch effect. This study explores the feasibility of in-situ grain refinement in 316L stainless steel fabricated by Directed Energy Deposition (DED) through the direct injection of titanium (Ti) particles into the melt pool. Unlike premixed powders, which often exhibit non-uniform distribution due to differences in density, morphology, and gas interactions, direct Ti injection provides real-time control over alloying composition and enables local microstructural tailoring.