Effect of heat treatment on mechanical properties of duplex steel SAF 2507 manufactured by DED

Abstract

This work is focused on the influence of heat treatment on the mechanical properties of duplex steel SAF 2507 produced by direct laser deposition (DLD). Duplex steels combine the advantages of ferritic and austenitic steels and reach excellent combination of mechanical and corrosion properties. The best properties are achieved by approximately equal phase ration of ferrite and austenite. Therefore, the proportion of austenite and ferrite before and after heat treatment was investigated within the study. Direct laser deposition technology was used for sample production. The DLD works on the principle of laser melting of the feedstock material (powder), which is carried by a protective gas into the nozzle. The material is successively deposited on the build platform. This technology can be used as an additive manufacturing process for surface repairs and component modifications. In this experimental study, the samples were deposited and subsequently subjected to the heat treatment. Solution annealing was chosen as the heat treatment method. The microstructure was characterized by LM, SEM and EBSD analyses. The mechanical tests were performed by a tensile testing on miniaturized specimens extracted from the experimental material in three orientations. The heat treatment had a fundamental effect on the proportion of austenite and ferrite, but also on the resulting mechanical properties. From the mechanical properties the maximum values of YS/UTS ∼ 680/830 MPa were reached and after heat treatment ∼ 540/760 MPa were reached.