Effect of B4C addition on the microstructure and mechanical properties of 304L austenitic stainless steel fabricated using laser powder bed fusion

The microstructure and mechanical properties of 304L austenitic stainless steel fabricated using laser powder bed fusion (L-PBF) upon the addition of B₄C are examined. The addition of B₄C induces the formation of Cr₂B at the cell boundaries and a multi-scale microstructural evolution that includes changes in the ferrite content, grain morphology, and crack formation, all of which significantly enhanced the yield strength of 304L at room temperature, due to the formation of Cr₂B and C in solid solution. However, the C in solution, combined with the formation of Cr₂B that consumes Cr from the alloy, increases the stacking fault energy (SFE) and, in turn, inhibits the stress-induced martensitic transformation. The primary deformation mechanism in the L-PBF 304L added with 1 wt.% B₄C transitions from twinning at room temperature to stress-induced martensitic transformation, due to the reduced SFE, at 77 K.