Influence of hot isostatic pressing post-treatment on the microstructure and mechanical behavior of standard and super duplex stainless steel produced by laser powder bed fusion

Abstract

This study investigates the properties of standard duplex steel 2205 and super duplex steel 2507 processed by laser powder bed fusion. The focus of the analysis is on the changes in microstructures and the mechanical properties caused by hot isostatic pressing (HIP) as post treatment. For that purpose, samples produced by laser powder bed fusion (LPBF) were exposed to hot isostatic pressing post-treatment followed by solution annealing. The properties of this condition were compared to properties of the duplex steels without post-heat treatment and of those of samples with only solution annealing as post-treatment.Both duplex steels had a predominantly ferritic structure after the LPBF process. Subsequent heat treatments were able to establish a ferritic-austenitic duplex structure. HIP applied before solution annealing leads to a coarsening of austenite grains and a reduction in porosity.All post-heat treated samples meet the minimum requirements of the standard DIN EN 10088-3 regarding tensile properties. An effect of hot isostatic pressing was seen in the fatigue strength. An increase in the fatigue strength was measured in both steels, which was mainly attributed to the decrease in inner defects size.