Werner Theisen, Johannes Boes, Luis Becker (Ruhr-Universität Bochum)

In the developing field of laser powder bed fusion (L-PBF), austenitic stainless steels, such as AISI 316L, have gained great importance owing to their excellent processability. However, the moderate strength of these steels limits their applicability. This can be counteracted by using nitrogen as an alloying element to improve both strength and corrosion resistance. Due to the fact that the N-solubility of Cr-Ni-austenitic steels is low, an austenitic N-alloyed stainless steel on Mn-base (X40MnCrMoN19-18-1) was processed by L-PBF, and the resulting microstructural and mechanical properties were investigated. The same material was also processed by hot isostatic pressing (HIP) and used as a reference state. In the L-PBF process, argon and nitrogen were used as process gases to investigate the influence of process atmosphere on the microstructure as well as on changes in the chemical composition during processing. The results show a minor decrease in the nitrogen content of the steel after L-PBF, depending on the process gas used.  The microstructure after L-PBF processing contained small precipitates that could be removed by a short solution-annealing treatment. The tensile properties of the steel in the L-PBF as built condition are comparable to those of the steel produced by hot isostatic pressing in terms of ultimate tensile strength but had lower elongation to fracture values. The ductility of the material could be enhanced by solution annealing without significant impairment of the ultimate tensile strength. The presentation is going to demonstrate that nitrogen-alloyed stainless steels can be processed by means of L-PBF and can extend the variety of appropriate steels towards applications with high requirements for the material strength without losing their chemical resistance.