On the origin of the high tensile strength and ductility of additively manufactured 316L stainless steel: Multiscale investigation

Abstract

We report that 316L austenitic stainless steel fabricated by direct laser deposition (DLD), an additive manufacturing (AM) process, have a higher yield strength than that of conventional 316L while keeping high ductility. More interestingly, no clear anisotropy in tensile properties was observed between the building and the scanning direction of the 3D printed steel. Metallographic examination of the as-built parts shows a heterogeneous solidification cellular microstructure. Transmission electron microscopy observations coupled with Energy Dispersive X-ray Spectrometry (EDS) reveal the presence of chemical micro-segregation correlated with high dislocation density at cell boundaries as well as the in-situ formation of well-dispersed oxides and transition-metal-rich precipitates. The hierarchical heterogeneous microstructure in the AM parts induces excellent strength of the 316L stainless steel while the low staking fault energy of the as-built 316L promotes the occurrence of abundant deformation twinning, in the origin of the high ductility of the AM steel. Without additional post-process treatments, the AM 316L proves that it can be used as a structural material or component for repair in mechanical construction.

Hierarchical Microstructure of Laser Powder Bed Fusion Produced Face-Centered-Cubic-Structured Equiatomic CrFeNiMn Multicomponent Alloy

“…The differences may be ascribed to the combination of fine cell structure, high density of dislocations, nano-inclusions, and residual stresses due to the SLM process. Former research [ 18 , 38 , 39 ] reported that the pre-existing dislocation networks induced by the SLM process provide substantially enhanced strength and ductility at the same time. The observation demonstrates the fact that by controlling the size of cell structures and chemical composition in conjunction with inducing dense dislocation networks and nano-inclusions, the SLM process can be utilized to reach the desired mechanical properties through optimizing the processing parameters.…”

Application of nanoparticles in cast steel: An overview

“…Oxide-dispersion strengthened steel was also manufactured by laser metal deposition, and its density was more than 99%. Compared with unreinforced steel, its hightemperature compression strength has also been enhanced [94,95] .…”

Non-oxide precipitates in additively manufactured austenitic stainless steel

“…However, none of the existing studies on precipitates in LMD 316LSS conclusively report the presence of non-oxides. In a very recent study, Barkia et al 28 reported the presence of an Mo-Cr-rich zone and an Mn–Mo–Cr-rich zone (around an Mn–Si–O precipitate) within the walls of an intragranular cellular solidification structure in their LMD 316LSS. However, these cell walls are known to be sites of preferential segregation of Mo and Cr 1 , and the reported presence of Mo–Cr and Mn–Mo–Cr zones can be considered only as circumstantial evidence of the presence of non-oxide precipitates.…”