Tensile Mechanical Properties of Micro-Selective Laser Melted 316L Stainless Steel
Received date: 2022-02-14
Revised date: 2022-06-16
Online published: 2022-09-26
Supported by
National Natural Science Foundation of China(51975240);Beijing Natural Science Foundation(2222093);Technical Development Foundation of China Academy of Machinery Science and Technology Group Co. Ltd(812201Q9)
Compared with selective laser melting (SLM), the micro-SLM (M-SLM) technology offers the advantages of small spot diameter (< 20 μm), high forming precision (20-50 μm), and surface roughness (Ra) of up 1 μm, which implies that the M-SLM technology provides great potential for promotion and application in communication electronics, biomedical, and other fields in the future. In this work, 316L stainless steel was prepared using M-SLM, and its tensile properties and fracture behavior were studied. The microstructures of transverse and longitudinal tensile specimens were also investigated. In addition, the fracture morphology was characterized and analyzed, and the grain orientation and grain-boundary-characteristic distribution in the near-section plastic-deformation zone were further analyzed using electron backscatter diffraction (EBSD). The results showed that the 316L stainless steel prepared by M-SLM had a cellular structure with a size of 100-300 nm inside the grains. The tensile fracture was dimple-shaped, and the average dimple diameter was 80-500 nm, which allowed the transverse average tensile strength of the 316L stainless steel to reach 692.1 MPa, the longitudinal average elongation after fracture was 54.6%, which were obviously better than that of the 316L stainless steel prepared using traditional SLM. The appearance of austenite Σ3 twin boundaries in the stretching process of the 316L stainless steel prepared by M-SLM was related to the grain orientation, which could more likely appear in grains with an orientation close to <111>. Further analysis indicated that the appearance of Σ3 grain boundaries blocked the connectivity of the special grain-boundary network. Statistical analysis of the coherent Σ3 (Σ3c) and incoherent Σ3 (Σ3ic) grain boundaries using the EBSD-based rectangular-section method revealed that the amount percentages of Σ3c and Σ3ic in the near-fracture region of the 316L transverse tensile specimen were approximately 43% and 57%, respectively. Meanwhile, the amount percentage of Σ3c in the same region of the 316L longitudinal tensile specimen increased to approximately 70%. The increase in the coherent Σ3c twin boundary reduced the total grain-boundary energy, which explained why the longitudinal tensile strength of the 316L stainless steel prepared by M-SLM was generally lower than the transverse tensile strength.
ZHANG Nan , ZHANG Haiwu , WANG Miaohui . Tensile Mechanical Properties of Micro-Selective Laser Melted 316L Stainless Steel[J]. Acta Metall Sin, 2024 , 60(2) : 211 -219 . DOI: 10.11900/0412.1961.2022.00041
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