Abstract
This work aims to show the impact of the allowed chemical composition range of AISI 316L stainless steel on its processability in additive manufacturing and on the resulting part properties. ASTM A276 allows the chromium and nickel contents in 316L stainless steel to be set between 16 and 18 mass%, respectively, 10 and 14 mass%. Nevertheless, the allowed compositional range impacts the microstructure formation in additive manufacturing and thus the properties of the manufactured components. Therefore, this influence is analyzed using three different starting powders. Two starting powders are laboratory alloys, one containing the maximum allowed chromium content and the other one containing the maximum nickel content. The third material is a commercial powder with the chemical composition set in the middle ground of the allowed compositional range. The materials were processed by laser-based powder bed fusion (PBF-LB/M). The powder characteristics, the microstructure and defect formation, the corrosion resistance, and the mechanical properties were investigated as a function of the chemical composition of the powders used. As a main result, solid-state cracking could be observed in samples additively manufactured from the starting powder containing the maximum nickel content. This is related to a fully austenitic solidification, which occurs because of the low chromium to nickel equivalent ratio. These cracks reduce the corrosion resistance as well as the elongation at fracture of the additively manufactured material that possesses a low chromium to nickel equivalent ratio of 1.0. A limitation of the nickel equivalent of the 316L type steel is suggested for PBF-LB/M production. Based on the knowledge obtained, a more detailed specification of the chemical composition of the type 316L stainless steel is recommended so that this steel can be PBF-LB/M processed to defect-free components with the desired mechanical and chemical properties.
Highlights
In times of climate change and the steadily increasing scarcity of resources, special requirements are placed on the production of components concerning sustainability [1].This is one of the reasons why interest in Additive Manufacturing (AM) processes has grown steadily in recent decades [2]
This work aims to correlate the acceptable alloy limits of steel AISI 316L according to ASTM A276 with the PBF-LB/M processability and the chemical and mechanical properties to give a recommendation which alloy composition might lead to an optimum of processability, chemical resistance, and mechanical properties of steel 316L
Three variants of the stainless steel AISI 316L that differ in their Creq /Nieq ratios were processed by means of PBF-LB/M
Summary
In times of climate change and the steadily increasing scarcity of resources, special requirements are placed on the production of components concerning sustainability [1].This is one of the reasons why interest in Additive Manufacturing (AM) processes has grown steadily in recent decades [2]. Due to the layer-by-layer built-up, a resource-efficient production of highly complex, net-shaped components is possible, enabling the high potential for lightweight construction to be fulfilled. It allows the timeefficient production of highly customized components without using product-specific tools [3]. The focused heat input introduced by the laser beam leads to small melt pools, whose heat is quickly dissipated by already solidified material volume. This results in high cooling rates and steep temperature gradients, resulting in high thermal stresses [5]. Acting as a trigger for cracking and component distortion, these stresses can significantly deteriorate component quality and properties [6]
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