Reciclagem de sucata de usinagem de aço inoxidável austenítico visando uso em manufatura aditiva

Abstract

Metals are widely used as raw materials in the manufacturing of industrial components. However, the exploration of mineral reserves, as well as extraction and beneficiation processes, require high energy consumption and often occur in environmentally sensitive regions. In this scenario, the circular economy emerges as a strategic alternative to reduce dependence on primary resources and minimize the energy impacts associated with metal production. Nevertheless, the feasibility of reuse depends on obtaining recycled materials with properties equivalent to those of the original raw material. In this work, the reuse of stainless steel chips, predominantly from the 316L alloy, was investigated as a raw material for powder production via gas atomization, followed by its application in additive manufacturing through Laser Powder Bed Fusion (LPBF). Initially, a systematic study was conducted on cleaning the chips, emphasizing the removal of organic contaminants, evaluating methods such as water washing, the use of an aqueous solution containing a commercial surfactant, and/or controlled heating. After defining the optimized cleaning method, the chips were cleaned and remelted to produce ingots, which were then gas-atomized. The resulting powders were sieved, resulting in predominantly spherical particles in the 20–75 µm size range, suitable for the LPBF process. Samples were then produced by LPBF and characterized regarding microstructure, phase formation, and mechanical properties. The results indicated that the most efficient cleaning method, evidenced by the greatest mass variation, was the combination of washing with an anionic surfactant solution (volume ratio of 0.005) and heating at 300 °C, as shown by the mass variation analyses. Heating without washing, although with a similar mass variation, performed similarly but caused color changes in the chips, suggesting possible carbon incorporation on the surface. The powders obtained were sieved, resulting in predominantly spherical particles in the 20–75 µm range with good flowability, suitable for LPBF processing. The powder produced from recycled material exhibited adequate flowability and morphology for LPBF processing. However, microstructural analysis of the samples manufactured by LPBF revealed the presence of cracks along grain boundaries, associated with solidification cracks, which mainly occurred due to the high carbon content in this material.