Extremely low-temperature tensile behavior of 316L stainless steel additively manufactured by laser powder bed fusion

초록

This study systematically investigated the extremely low-temperature (4.2 K) tensile behavior of laser powder bed fusion (LPBF)-fabricated 316L stainless steel (SS316L) in comparison with a hot isostatic pressed (HIP) counterpart to clarify the influence of LPBF-driven microstructure on discontinuous plastic flow (DPF) behavior. The LPBF-fabricated SS316L exhibited a hierarchical heterogeneous microstructure consisting of grain- and cellscale substructures with a dense dislocation network, whereas the HIP-treated alloy showed a homogeneous, fully recrystallized grain structure due to the elimination of substructures during the HIP process. The mechanical behavior at 4.2 K revealed a strong dependence on the underlying microstructure. In the early deformation stage, the LPBF-fabricated sample exhibited pronounced DPF and irregular stress fluctuations originating from the LPBF-driven substructure that promoted frequent dislocation interactions and local mechanical instability. Despite the reduced kinetics of deformation-induced martensitic transformation (DIMT) due to its high residual dislocation density, DPF remained dominant under deep cryogenic conditions, governed by dislocation cell structures and heterogeneous grain boundaries. These findings reveal that LPBF-driven microstructures play a key role in controlling mechanical instability and local strain evolution at 4.2 K, offering new insight into the microstructure-property relationship of cryogenic structural materials.

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