Effect of Deep Cryogenic Treatment on the Mechanical Properties and Defect Tolerance of Selective-Laser-Melted 316L Stainless Steel

In this study, the effects of deep cryogenic treatment on the microstructure and mechanical properties of 316L stainless steel fabricated by selective laser melting were investigated. Two types of samples were subjected to comparative experiments: (i) as printed (AP), and (ii) deep cryogenic treatment (DCT). Microstructural analysis revealed that DCT reduced the sample porosity from 1.05 to 0.36%. In terms of mechanical properties, the DCT samples exhibited tensile and yield strengths of 736 MPa and 541 MPa, respectively, which are significantly higher than those of conventionally cast parts. The elongation reached 59%, a crucial factor for applications requiring material flexibility. However, fatigue test results showed a reduction in the fatigue performance of DCT samples. The fatigue limit was predicted using extreme value statistical analysis and sample sectioning methods, with the prediction error within 10%. The Kitagawa–Takahashi diagram and EI-Haddad model were used to evaluate the safety performance of the material, and the critical defect sizes of the samples were determined. The prediction results were consistent with the statistical analysis of crack source defect sizes in fractured samples.