Effect of Heat Treatments on Residual Stress and Properties of AISI 316L Steel Processed by Directed Energy Deposition
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JMEPEG https://doi.org/10.1007/s11665-020-05061-9
Effect of Heat Treatments on Residual Stress and Properties of AISI 316L Steel Processed by Directed Energy Deposition Alberta Aversa, Gabriele Piscopo, Alessandro Salmi, and Mariangela Lombardi (Submitted April 3, 2020; in revised form July 23, 2020) AISI 316L stainless steel samples were produced by means of laser powder-directed energy deposition using optimized building conditions with two different deposition strategies. The samples, in the as-built state, were at first characterized in terms of microstructure, hardness and residual stresses by the incremental hole-drilling strain-gauge method. The results highlighted that the deposition strategy mainly affects the residual stress values, while the material hardness value is not strongly varied. The distribution of the residual stresses along the sample height was also evaluated by measuring the stress at different distances from the building platform. Furthermore, some samples underwent a homogenizing heat treatment for 2 h at 600 and 800 °C and were characterized and compared with the as-built ones. The results showed that the suggested heat treatments allow not only a reduction in residual stresses but also the homogenization of the microstructure confirmed by comparing the variations of the Vickers hardness values along the building direction. Tensile tests were also performed on the as-built and heat-treated samples in order to investigate the effect of the heat treatment on the tensile properties of the material. Keywords
316L, additive manufacturing, directed energy deposition, heat treatments, mechanical properties, residual stress
1. Introduction Directed energy deposition (DED) is a class of additive manufacturing (AM) processes that allow the production of metallic components by melting, by means of a focused energy source, the metallic material which is directly fed in specific areas of the building volume. DED technologies gained a large interest mainly thanks to the possibility to repair metallic components and produce large and functionally graded parts. In particular, laser powder-DED (LP-DED) uses a laser beam as energy source and the material in the form of powder. LP-DED was recently used to process various alloys such as AlSi10Mg, Ti-6Al-4V, Inconel 625 and AISI 316L stainless steel (SS) (Ref 1-4). The results showed that it is possible to produce dense and crack-free parts with these powders and that, thanks to the rapid cooling, the as-built components are constituted by a fine microstructure and interesting mechanical properties. In particular, the microstructure and mechanical properties of LP-DED 316L parts have been investigated by several authors in recent years (Ref 5-7) The main findings are that the as-built microstructure is strongly correlated with the thermal
Alberta Aversa and Mariangela Lombardi, Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin, Italy; and Gabriele Piscopo and Alessandro Salmi, Department of Managemen
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