Crystallographic orientation dependence of Charpy impact behaviours in stainless steel 316L fabricated by laser powder bed fusion

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Despite the extensive research on the mechanical properties of stainless steel 316L (SS316L) produced by laser powder bed fusion (LPBF), only a handful of studies have investigated its impact performance even though it is critical for structural applications experiencing rapid loading. In this study, the crystallographic-orientation-dependent Charpy impact behaviours of LPBF-SS316L were systematically investigated. Samples with their longitudinal directions (LDs) along the 〈100〉, 〈110〉 and 〈111〉 crystallographic directions were tested at both room temperature (RT) and liquid nitrogen temperature (LNT). At RT, the 〈100〉 and 〈111〉 samples exhibited similar impact toughness, while that of the 〈110〉 samples was the lowest. At LNT, the absorbed energy of the 〈100〉 and 〈111〉 samples experienced varying decreases. However, the impact toughness of the 〈110〉 samples did not suffer from the cryogenic temperature, exhibiting the highest absorbed energy value at LNT. The percentage of the shear area on the fracture surface was well correlated with the impact toughness. EBSD analysis showed that all the samples fractured at RT contained deformation twins. The lower impact toughness of the 〈110〉 samples was attributed to the slow strain hardening recovery due to their moderate twinning-induced plasticity (TWIP) effect under tension. At LNT, deformation twinning still prevailed in the 〈100〉 samples, while the 〈110〉 and 〈111〉 samples favoured strain-induced martensite, featuring dispersed ε-martensite and a considerable amount of α'-martensite, which led to strong transformation-induced plasticity (TRIP) effect. In particular, the 〈110〉 samples were characterized by a more widespread strain-induced martensitic transformation, resulting in their highest impact toughness at LNT among the three orientations. This study provides valuable insights into the design of crystallographic texture of LPBF-SS316L towards better impact properties for future structural applications. • Impact behaviours along the 〈100〉, 〈110〉 and 〈111〉 directions of LPBF-SS316L. • Great impact toughness at room temperature and liquid nitrogen temperature (LNT). • No deterioration in impact toughness of the 〈110〉 samples at LNT. • ε-martensite in LPBF-SS316L after deformation. • Correlations between impact toughness and deformed microstructure.