Improving the Defect Tolerance of PBF-LB/M Processed 316L Steel by Increasing the Nitrogen Content

Stern, F. and Becker, L. and Cui, C. and Tenkamp, J. and Uhlenwinkel, V. and Steinbacher, M. and Boes, J. and Lentz, J. and Fechte-Heinen, R. and Weber, S. and Walther, F.

Volume: Pages:
DOI: 10.1002/adem.202200751
Published: 2022

Nitrogen (N) in steels can improve their mechanical strength by solid solution strengthening. Processing N-alloyed steels with additive manufacturing, here laser powder bed fusion (PBF-LB), is challenging as the N-solubility in the melt can be exceeded. This degassing of N counteracts its intended positive effects. Herein, the PBF-LB processed 316L stainless steel with increased N-content is investigated and compared to PBF-LB 316L with conventional N-content. The N is introduced into the steel by nitriding the powder and mixing it with the starting powder to achieve an N-content of approximately 0.16 mass%. Thermodynamic calculations for maximum solubility to avoid N outgassing and pore formation under PBF-LB conditions are performed beforehand. Based on the results, a higher defect tolerance under fatigue characterized by Murakami model can be achieved without negatively influencing the PBF-LB processability of the 316L steel. The increased N-content leads to higher hardness (+14%), yield strength (+16%), tensile strength (+9%), and higher failure stress in short time fatigue test (+16%). © 2022 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH.

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