Effects of AlN addition into AISI 316L on melt pool stability and microstructural evolution during laser powder bed fusion

Abstract

316L stainless steel that was modified by addition of reducing agent was manufactured by laser powder bed fusion using 316L powder that included 1 wt% Aluminum nitride (AlN), named 316L+AlN and compared with the as-built 316L stainless steel that was manufactured using only 316L powder. AlN addition diminished the oxygen content from 468 ppm (316L) to 244 ppm (316L+AlN), but increased the nitrogen content from 842 ppm (316L) to 1293 ppm (316L+AlN). Reduction behavior was faster in 316L+AlN steel than in 316L steel. Epitaxial grains were larger in 316L+AlN steel than in 316L steel within the different textural orientations between two different sets; this difference correlated well with the shape and temperature distribution of the melt pool. The inclusions in 316L+AlN steel were alumina, not nitride; this result means that nitride was supersaturated. The yield strength was increased from 485.4 MPa to 583.2 MPa when 1 wt% of AlN was added in 316L. 316L+AlN steel was stronger than 316L steel, primarily because of increased dislocation density in 316L+AlN steel.