Papers by Keyword: 316L

Abstract: This study examines the influence of Wire Arc Additive Manufacturing (WAAM) param eters on the microstructure and mechanical properties of AISI 316L stainless steel, comparing out puts from two different systems: the Fronius TransPuls Synergic 2700 CMT and the Kemppi X5 500 Pulse+. By employing Electron Backscatter Diffraction (EBSD) for microstructural characterization alongside tensile and hardness tests, we investigated how different printing speeds, wire feed rates, and free wire lengths impact the material’s properties. The Fronius system produced parts with a fine, uniform, columnar grain structure, leading to more isotropic mechanical properties. In contrast, the Kemppi system resulted in coarser grains with delta ferrite, increasing ductility but also introducing anisotropy. The geometry and hardness of the parts also showed significant variations, underscoring the critical need for parameter optimization in WAAM to achieve desired material characteristics for specific applications. These findings highlight the importance of process parameter tuning to minimize defects and enhance the consistency and performance of additively manufactured parts.

Abstract: This study was initiated to investigate the material characteristics of binder jet (BJ) manufactured austenitic stainless steel 316L, focusing specifically on the less studied bronze infiltrated version of this material. While BJ technology offers a compelling alternative to the current market leader laser powder bed fusion, all additive manufacturing methods are susceptible to porosity, which adversely affects the fatigue properties of parts, resulting in inferior fatigue life compared to traditionally manufactured counterparts. In this study, we explore the novel application of severe shot peening (SSP) as a post-processing method to enhance fatigue life. Through comprehensive microstructural analysis utilizing EBSD, mechanical properties testing via tensile testing, and fatigue life analysis using flexural bending fatigue testing, we demonstrate that SSP treatment induces surface modification, leading to increased material strength albeit with a trade-off in ductility. Moreover, our findings reveal a significant improvement in the fatigue life of the material. Utilizing SSP, we observed that the fatigue limit of the material more than doubled, surpassing the performance of the sheet metal counterpart of the same material. These results underscore the potential of SSP as an attractive method for property enhancement in additive manufacturing.

Abstract: This study investigates the mechanical properties and microstructure of 316L stainless steel fabricated using laser powder bed fusion (PBF-LB) additive manufacturing with different layer thick nesses and orientations. Impact toughness is evaluated under various conditions as well as bending fatigue performance to understand the influence of layer thickness and surface quality on fatigue lim its. Microstructural analysis using scanning electron microscopy (SEM) provides insights into grain structure. Key findings include the superior impact toughness of the vertical orientation, particularly notable in specimens with a layer thickness of 40 µm. Bending fatigue tests revealed distinctive behav ior influenced by layer thickness and surface quality, with the 80 µm thickness and vertical orientation demonstrating lower fatigue limits. These insights contribute to optimizing manufacturing processes and enhancing material suitability for diverse applications.

Abstract: Binder jetting is a rapidly evolving additive manufacturing technique, challenging the dominance of laser powder bed fusion in metal fabrication. This study focuses on the material properties of austenitic stainless steel 316L produced via binder jet technology. Porosity remains a significant challenge across additive manufacturing methods, adversely affecting material properties and fatigue life. To address this issue, we propose a novel approach employing severe shot peening as a post-processing treatment to enhance the material's characteristics. Microstructural analysis, including electron backscatter diffraction (EBSD), coupled with tensile testing, was conducted to evaluate the mechanical properties. Additionally, fatigue behavior was investigated under both axial and flexural bending loading conditions. The results revealed a substantial increase in material strength achievable through the post-treatment. Notably, the fatigue limit of the material in bending fatigue was elevated from 120 MPa to 190 MPa, indicating a significant enhancement in fatigue performance. This study contributes new insights into the enhancement of fatigue resistance in binder jet-manufactured 316L stainless steel through surface modification techniques. The findings underscore the potential of severe shot peening as an effective strategy to improve material properties and expand the applicability of binder jet printing in demanding industrial applications.

Abstract: Additive manufacturing, specifically Laser Powder Bed Fusion (PBF-LB), has gained prominence for its capability to produce complex near-net-shaped components. While PBF-LB offers advantages such as lightweight construction and cost-effectiveness, post-processing remains crucial to meet specific design requirements. This study investigates the post-processing technique of severe shot peening (SSP) on PBF-LB-manufactured 316L stainless steel, a material widely used for its favorable mechanical properties and corrosion resistance. The research focuses on the enhancement of bending fatigue properties through SSP treatment, examining the influence of material thickness on fatigue behavior. Comparative analysis reveals the effectiveness of SSP in significantly improving fatigue strength irrespective of variations in material thickness. Mechanical properties are explored for different thicknesses subjected to SSP treatment. Electron Backscatter Diffraction (EBSD) is employed to scrutinize the surface properties of the samples, providing knowledge on the microstructural changes induced by SSP. The study contributes to the understanding of the role of material thickness in the context of SSP treatment, offering a comprehensive exploration of the mechanical and fatigue characteristics of PBF-LB-manufactured 316L stainless steel.

Abstract: Laser powder bed fusion (PBF-LB) technique can currently offer the lowest surface roughness among all available techniques for metal additive manufacturing. Still the measured values for R_a can easily be over 10 μm depending on the used layer thickness and printing parameters. The current work focuses on improving the surface roughness by utilizing dry electropolishing machine. While suitable for many materials, the material selected for this study is one of the most used in PBF-LB manufacturing, stainless steel 316L. In addition, multistep pre-grinding with the grade of the final finish varied was used to investigate what is the most efficient way to distribute manual preparation work and automated polishing to reach the desired surface roughness. Furthermore, severe shot peening was used before the polishing to study the effect on residual stresses and fatigue life of the material. Laser optical microscopy was used to investigate the surface properties and it was found that dry electropolishing with pre-grinding could be succesfully used to obtain average roughness levels as low as 0.13 μm. The highest reductions in surface roughness were reached with the rougher initial surfaces where it could be reduced by 80% at best. Residual stresses measured after the severe shot peening were preserved after the polishing but did not result in increased fatigue strength.

Abstract: This study aims to investigate the influence of isothermal annealing on the residual stresses and fatigue properties of a 316L austenitic stainless steel, manufactured by the laser powder-bed fusion (LPBF), possessing a high density of 99.98%. Residual stresses were evaluated using the X-ray diffraction techniques. High-cycle fatigue tests were performed on cylindrical samples manufactured in both horizontal and vertical orientations, subjected to force-controlled axial fully reversed loading. Following fabrication, the samples underwent isothermal annealing in a furnace either at 600 °C for 120 minutes or at 900 °C for 30 minutes. Subsequently, the samples were machined to their final dimensions and electropolished to a mirror surface finish. Preliminary findings revealed that increasing the annealing temperature effectively reduced the surface residual stresses. However, this reduction did not lead to an improvement in the fatigue resistance of this nearly fully dense material in the high-cycle fatigue regime. Interestingly, the structure annealed at 600 °C exhibited a higher fatigue strength compared to the structure annealed at 900 °C, with no discernible difference between the printing directions. Fracture surfaces and microstructural features examined using light and electron microscopy revealed that cracking was primarily initiated at surface defects or slip bands. These results highlight the complex interplay between residual stresses, microstructure, strength, and fatigue behaviour of LPBF 316L austenitic stainless steel. Further analysis and investigations are required to fully understand the underlying mechanisms and develop strategies for enhancing the fatigue performance of additive manufactured components.

Abstract: The aim of our study was to determine changes in the microstructure and mechanical properties of AISI 316L steel processed by additive SLM technology which will be induced by additional processing using HIP technology and solution annealing. The specimens for this experiment were made in the form of bars with a diameter of 5 mm for tensile testing. The specimens were additively manufactured in the vertical direction with respect to the position of the build plate using standard process parameters. The HIP processing of the specimens was performed at a temperature of 1150 °C and pressure of 150 MPa. Some of the specimens were heat treated using solution annealing at 1150 °C after the SLM and HIP processes. The analyses performed consisted of metallographic analysis of the microstructure using light and scanning electron microscopy methods, which were further complemented by basic mechanical property tests, namely tensile testing and HV1 hardness measurements. The tensile test showed that the solution annealing of the printed specimens reduced the ultimate strength from 545±6.2 MPa to 508±0.0 MPa and increased the ductility from 44±5.4 % to 56±0.4 %. The HIP process reduced the ultimate strength to 522±2.7 MPa and the further annealed specimens to 514±1.8 MPa. The ductility of the specimens after HIP treatment was higher than that of the additively manufactured specimens, corresponding to 52±0.3 %. After solution annealing, it reached values like those of the specimens annealed after 3D printing. The metallographic analysis carried out showed a positive effect of the HIP process on the porosity achieved after 3d printing, whose volume was reduced as a result.

Abstract: Laser powder bed fusion manufactured (PBF-LB) austenitic stainless steel 316L offers higher strength than traditionally manufactured counterparts. Further improvement can be obtained with suitable surface modification. This work focuses on improving the material qualities with the aid of severe shot peening (SSP), which can increase the surface hardness, reduce roughness and produce grain refinement and compressive residual stresses on the surface. These qualities are all beneficial for the fatigue life of the material. Material was studied in two conditions: as built and heat treated (HT) at 1100 °C and the effect of SSP on both. The results showed clear microstructural changes on both structures leading to increased strength. The fatigue strength of as built material benefits greatly from the SSP treatment, but when performed on a high temperature HT material the benefits are negligible. However, in applications where the parts are subjected to bending forces the surface modification plays a role also with the HT material.

Abstract: Additive manufactured (AM) 316L and Inconel 718 (IN718) parts using laser powder bedfusion technique and the weldability of the mixed pair by laser welding was investigated in this paper.The effect of prior heat treatment of the materials was also taken in to consideration. The motivationbehind this work was to investigate if hybrid products could be manufactured from these materials formore cost­efficient production of AM products. The results showed good reliability of the welds asthe tensile results were on par with the 316L base material. The hardness of the weld fusion zone was50 HV lower compared to the 316L base material hardness at 225 HV. In general, the results showedlaser welding is a very promising method for joining these printed materials and can be utilized asanother tool when integrating these materials into a design.