Laser Additive Manufacturing of Duplex Stainless Steel via Powder Mixture

Abstract

Laser additively manufactured duplex stainless steels contain mostly ferrite in the as-built parts due to rapid solidification of the printed layers. To achieve duplex microstructures (ferrite and austenite in roughly equal proportions) and, thus, a good combination of mechanical properties and corrosion resistance, an austenitic stainless steel powder (X2CrNiMo17-12-2) and a super duplex stainless steel powder (X2CrNiMoN25-7-4) were mixed in different proportions and the powder mixtures were processed via PBF-LB/M (Laser Powder Bed Fusion) under various processing conditions by varying the laser power and the laser scanning speed. The optimal process parameters for dense as-built parts were determined by means of light optical microscopy and density measurements. The austenitic and ferritic phase formation of the mixed alloys was significantly influenced by the chemical composition adjusted by powder mixing and the laser energy input during PBF-LB/M. The austenite content increases, on the one hand, with an increasing proportion of X2CrNiMo17-12-2 in the powder mixtures and on the other hand with increasing laser energy input. The latter phenomenon could be attributed to a slower solidification and a higher melt pool homogeneity with increasing energy input influencing the phase formation during solidification and cooling. The desired duplex microstructures could be achieved by mixing the X2CrNiMo17-12-2 powder and the X2CrNiMoN25-7-4 powder at a specific mixing ratio and building with the optimal PBF-LB/M parameters.

A Comparative Investigation of Duplex and Super Duplex Stainless Steels Processed through Laser Powder Bed Fusion

“…In other studies, the authors developed new alloys, suitable for LPBF, by the dry mixing of elemental powders and/or pre-alloyed powders, allowing them to create custom duplex and super duplex powder blends with tailored chemical compositions. The aim was to promote austenite formation in the as-built condition [25][26][27].…”

Post-Processing Effect on the Corrosion Resistance of Super Duplex Stainless Steel Produced by Laser Powder Bed Fusion

“…Microcrystalline grain boundary austenite (GBA) was observed at the grain boundaries, exhibiting an allotriomorphic shape and morphology ( Figure 4 b). LPBF-related studies [ 5 , 6 , 7 , 8 , 9 , 11 , 12 , 14 , 21 , 28 , 29 ] have reported that extremely high cooling rates inhibit the formation of sigma phase in as-printed conditions. Additionally, an excess of nitrogen saturation within the ferrite matrix has been found to induce the formation of chromium nitride precipitates due to the formation of Cr-rich regions at grain boundaries (GB).…”

“…In the background of additive manufacturing, there is a growing interest also in DSS [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. This is evidenced by the development of Super-DSS grade 2507 (EN 1.4410) powder, which is specifically designed for additive manufacturing processes.…”

Synthesis and Characterization of Innovative Fe–Cr–Mn Ferritic Stainless Steel by Laser Powder Bed Fusion

“…The austenitic and ferritic-austenitic microstructures can be produced via the partial substitution of Ni by Mn [17] or the mixture of austenitic stainless steel powders and super duplex stainless steel powders in different proportions. [18] The printing pores, microstructure, mechanical properties, and corrosion resistance were characterized in the previous studies. [13,17] It was found that the introduction of nitrogen tends to increase porosity due to the limited solubility of nitrogen in the steel matrix.…”