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

Abstract

The aim of this paper was to compare duplex (DSS) and super duplex stainless steel processed by laser powder bed fusion (LPBF) based on the process parameters and microstructure–nanomechanical property relationships. Each alloy was investigated with respect to its feedstock powder characteristics. Optimum process parameters including scanning speed, laser power, beam diameter, laser energy density, and layer thickness were defined for each alloy, and near-fully dense parts (>99.9%) were produced. Microstructural analysis was performed via optical (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The samples were subjected to stress relief and high-temperature annealing. EBSD revealed the crystallographic orientation and quantified the phases in the as-built and annealed sample conditions. The as-built samples revealed a fully ferritic microstructure with a small amount of grain boundary austenite in the SDSS microstructure. High-temperature solution annealing resulted in the desired duplex microstructure for both alloys. There were no secondary phases present in the microstructure after both heat treatments. Nanoindentation generated nanomechanical (modulus) mapping grids and quantified the nanomechanical (both hardness and modulus) response; plasticity and stress relief were also assessed in all three conditions (as-built, stress-relieved, and annealed) in both DSS and SDSS. Austenite formation in the annealed condition contributed to lower hardness levels (~4.3–4.8 Gpa) and higher plastic deformation compared to the as-built (~5.7–6.3 Gpa) and stress-relieved conditions (~4.8–5.8 Gpa) for both alloys. SDSS featured a ~60% austenite volume fraction in its annealed and quenched microstructure, attributed to its higher nickel and nitrogen contents compared to DSS, which exhibited a ~30% austenite volume fraction.

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).…”

“…The microstructures consist mostly of ferrite with small amounts of austenite found mainly at grain boundaries and within the ferritic matrix, as well as limited intragranular austenite. LPBF presents challenges in achieving a well-balanced duplex microstructure due to its rapid cooling rate, often resulting in a predominantly ferritic microstructure in the as-printed condition [ 5 , 8 , 21 ]. To overcome this limitation, post-processing annealing is necessary [ 13 , 16 ].…”

“…Additionally, stress-relief annealing can be applied after additive manufacturing to optimize the properties of DSS components. Recent research on additive manufacturing of DSS addresses such issues [ 9 , 10 , 13 , 15 , 16 , 21 ]. The printed microstructure of DSS can contain precipitates of secondary phases, such as sigma, and chromium nitrides, in addition to fully ferritic ones [ 13 ].…”

Microstructural and Hall–Petch Analysis of Additively Manufactured Ferritic Alloy Using 2507 Duplex Stainless Steel Powder

“…The limited literature on PBF-LB-processed DSS alloys [12][13][14][15][16][17][18][19][20] is primarily focused on documenting the effects of processing parameters on the porosity, with relatively less attention devoted to microstructural analysis and understanding of microstructure-mechanical behavior relationships. For example, Davidson and Singamneni [14,15] conducted two investigations to examine the impact of processing conditions on the build quality of DSS, specifically focusing on porosity and certain microstructural features.…”

Correction: Gargalis et al. A Comparative Investigation of Duplex and Super Duplex Stainless Steels Processed through Laser Powder Bed Fusion. Metals 2023, 13, 1897

“…In the original publication [1], there was a mistake in Table 6 as published. We erroneously reported the values included in Table 6, which should be deleted.…”