Flaw type dependent tensile properties of 316L stainless steel additively manufactured by laser powder bed fusion

Abstract

In this laser powder bed fusion (LPBF) study for 316 L stainless steel (316 L SS), the laser scan speed was varied to produce samples with keyhole (KH) and lack of fusion (LoF) flaws, each with three levels of density (i.e., >97%, ∼98%, and ∼99%). KH and LoF flaws were characterized by circularity, size, and aspect ratio from extensive image analysis of optical micrographs. The samples were tested in uniaxial tension to correlate the flaw characteristics with yield strength (YS), ultimate tensile strength (UTS), and elongation at failure (EL%). Results showed that the circularity decreased, while the size and aspect ratio increased for both KH and LoF flaws when the laser scan speed (at constant power) deviates from the LPBF parameters that yields nearly fully dense 316 L SS. Additional to the influence of the density, the YS and UTS of the samples showed more sensitivity to the LoF than KH, while the EL% was comparable between the two types of flaws when the porosity is below 2%. The difference in mechanical properties for the 316 L samples containing KH and LoF flaws with similar density was minimal because of the intrinsically high ductility of the alloy.