Tensile Properties of Selective Laser Melted 316L Stainless Steel
YU Chenfan1, ZHAO Congcong1, ZHANG Zhefeng2, LIU Wei1()
1.School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China 2.Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
YU Chenfan, ZHAO Congcong, ZHANG Zhefeng, LIU Wei. Tensile Properties of Selective Laser Melted 316L Stainless Steel. Acta Metall Sin, 2020, 56(5): 683-692.
Selective laser melting (SLM), as the most common additive manufacturing (AM) method, is capable of manufacturing metallic components with complex shape layer by layer. Compared with conventional manufacturing technologies such as casting or forging, the SLM technology has the advantages of high degree accuracy, high material utilization rate and environmentally friendly, and has attracted great attention in the fields of aerospace, nuclear power and medicine. The 316L austenitic stainless steel is widely used in the industrial field because of the excellent corrosion resistance and plasticity. It is also one of the commonly used material systems for SLM. In this work, the tensile properties and fracture mechanism of 316L stainless steel fabricated via SLM technology were investigated. The microstructure of the SLMed 316L specimens after tensile fracture was characterized and analyzed. The results show that the SLMed 316L stainless steel has a relatively desirable combination of strength and ductility, and its tensile performance is obviously better than that of 316L stainless steel prepared by traditional methods. The nanometer-scale cell structure inside the grain contributes to the improvement of strength. Deformation twins were observed in the SLMed 316L stainless steel after tensile test. The appearance of twins is oriented-dependent, and it is easy to occur in the grain with the direction near <110>-<111>.
Fig.2 Low (a) and high (b) magnified SEM images of 316L stainless steel powders
Fig.3 SEM images showing the cellular structures in selective laser melted (SLMed) 316L stainless steel (a) cellular structures (top side) (b) cellular structures near grain boundary (lateral side) (c) cellular structures near melt pool boundary (lateral side)
Fig.4 Tensile engineering stress-strain curves of 316L stainless steel fabricated by SLM
Sample
Rm
MPa
σ0.2
MPa
δ
%
UT
106 J·m-3
Horizontally built
665.9
550
53.2
337.8
Vertically built
575.4
520
71.9
431.2
Table 1 Tensile properties of SLMed 316L stainless steel with different building directions
Fig.5 Comparisons of tensile properties of SLMed 316L stainless steel and counterparts fabricated by traditional methods[22,23,24,25,26,27,28]
Fig.6 Low (a, b) and high (c, d) magnified SEM images showing the tensile fracture surfaces of vertically built (a, c) and horizontally built (b, d) SLMed 316L stainless steel samples (Figs.6b and d indicate dimple fracture and pore defect, respectively)
Fig.7 EBSD analyses of SLMed 316L stainless steel with different building directions after tensile fracture Color online (a) inverse pole figure (IPF) orientation map of horizontally built sample (b) band contrast map of horizontally built sample (c) IPF orientation map of vertically built sample (d) band contrast map of vertically built sample (IPF∥loading direction, the red lines represent twin boundaries)
Fig.8 Misorientation distributions of SLMed 316L stainless steel with different building directions before (a) and after (b) tensile fracture
Fig.9 EBSD IPF orientation map (a) and diffraction band contrast maps (b, c) of SLMed 316L stainless steel (horizontally built sample) after tensile deformation, and misorientation result for line AB in Fig.9c (d) (Fig.9c shows the enlarged view of square area in Fig.9b, the red lines in Fig.9b and c represent twin boundaries) Color online
Fig.10 IPF along tensile axis direction showing the grain orientations obtained from SLMed 316L stainless steel (horizontally built sample) Color online
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