Influence of Deposition Parameters on the Building rate, In-Situ Formation of Austenite and Tensile Properties of SAF 2507 SDSS Fabricated by Directed Energy Deposition

Abstract

Industry applications of duplex stainless steels require a two-phase microstructure with a nearly balanced austenite-ferrite content to achieve good mechanical properties and good corrosion resistance. The most widespread additive manufacturing method such as laser powder bed fusion provides nearly fully ferritic microstructures due to the very high cooling rate, and the post-processing heat treatment must be performed. In contrast, other additive manufacturing methods, such as directed deposition methods, reach lower cooling rates and enable to obtain an equal ferrite–austenite ratio directly in the microstructure of the as-built state. In this work, the super duplex stainless steel SAF 2507 was deposited by directed energy deposition. The process parameters, namely, the laser power, laser beam spot, and powder feed rate, were varied to investigate the impact of the energy area density on the microstructure and tensile properties. A decrease in the energy area density caused an increase in the austenite content of 48 vol% and a numerical simulation of the sample temperature distribution inside the block during deposition, explaining the relationship between the amount of in situ formed austenite and the deposition parameters, was provided. Simultaneously, the deposition rate increased by more than five times. In contrast, the samples deposited at a higher building rate are characterized by greater porosity and lower elongation values in the vertical direction. The effect of the deposition parameters on the yield strength is low.

Graphical Abstract