In-situ interstitial alloying during laser powder bed fusion of AISI 316 for superior corrosion resistance

Abstract

• L-PBF of a 316L admixed with 2.5 wt% Cr 2 N enhanced the Cr and N contents as compared to 316L. • A nitrogen content of 0.31 wt% in solid solution was obtained. • The parts were fully austenitic, exhibiting the favorable cellular substructure. • The enhanced nitrogen content improved corrosion resistance and hardness as compared to 316L. • The results show an alternative to manufacturing of high nitrogen steels. The present work explores for the first time additive manufacturing of powder mixtures consisting of Chromium Nitride (Cr 2 N) and AISI 316L with laser powder bed fusion (L-PBF). The addition of 2.5 wt% Cr 2 N to an AISI 316L powder resulted in the successful dissolution of both chromium and nitrogen into a fully austenitic stainless steel microstructure. The nitrogen content was augmented from 0.09 wt% in the as-delivered AISI 316L powder to 0.31 wt% in the L-PBF built part, causing a slight expansion of the austenite lattice. Elongated austenite grains with an internal cellular substructure were obtained in both the Cr 2 N modified 316L and the 316L specimens manufactured by L-PBF. The addition of nitrogen (and chromium) from Cr 2 N resulted in a Vickers hardness increase of about 40 HV 0.1 , mainly by interstitial solid solution strengthening. The modification of 316L by the addition of Cr 2 N significantly improved the corrosion resistance. The improved hardness and corrosion resistance while retaining the manufacturability and cellular microstructure illustrate the potential for modifying the composition and properties of L-PBF 316L with targeted dosing with Cr 2 N powders.