Estudo do comportamento mecânico e formação de fases em aços 316l modificados com boro fabricados por manufatura aditiva

Abstract

The addition of boron to steels has been identified as a promising strategy for promoting microstructural refinement and increasing mechanical strength, particularly in materials produced by laser powder bed fusion (LPBF). However, the mechanisms responsible for these modifications are not yet fully understood. In this context, the present work investigated the effect of boron addition on alloys based on AISI 316L stainless steel produced by LPBF, comparing commercial 316L with the modified Mo3 and Mo4 alloys, both containing 0.75 wt.% boron and different molybdenum contents of 3.0 and 4.0 wt.%, respectively. Initially, the processing parameters were optimized using a Box-Behnken experimental design, resulting in the selection of 300 W laser power, 250 mm/s scanning speed, 70 µm hatch spacing, and 30 µm layer thickness. The alloys were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Additionally, the effect of cooling rate on microstructural evolution was evaluated by casting the alloys in a stepped mold, using different mold sections to obtain distinct cooling conditions during solidification. The cast samples were characterized by SEM, XRD, and hardness testing. The results showed that boron addition promoted grain refinement, reduced crystallographic texture intensity, and increased hardness and mechanical strength. The Mo4 alloy exhibited residual ferrite and Cr- and Mo-rich precipitates, with the Mo₃B₂ and Cr₂B phases identified by TEM. In the cast alloys, a reduction in cooling rate promoted an increase in interdendritic spacing and greater ferrite retention. The modified alloys achieved ultimate tensile strengths above 1000 MPa, mainly associated with microstructural refinement and boride formation.