**4. Conclusions**

The use of 21NiCrMo2 steel in the AM process represents a significant improvement in the number of available materials from the low-alloy steel group. The research presented here proves the possibility of using such materials in PBF-LB/M processes. The developed method of process parameter selection allowed us to identify an exact range which ensured that we could reach a very high parts density, equal to 99.7%. An essential aspect of this research is the possibility of implementing the developed mathematical model in relation to other materials dedicated to the PBF-LB/M process. Through the consideration of the obtained results, we drew the following conclusions.


clearly confirms the possibility of using 21NiCrMo2 steel as an alternative to 20MnCr5 or 16MnCr5 steel in the discussed scope of research.

Further research will be focused on the influence of thermochemical treatment (carburizing hardening, and tempering) on the microstructure, as well as mechanical and fatigue properties. This is a crucial step in order to enable more advanced applied research in this field.

**Author Contributions:** Conceptualization, J.Ł., L.S. and K.G.; methodology, J.Ł., J.K., K.G. and L. ´ S.; ´ software, J.Ł. and J.K.; validation, J.Ł., J.K., J.T. and I.S.; formal analysis, J.Ł. and K.G.; investigation, J.Ł., J.T., M.W. and I.S.; resources, M.K. and I.S.; data curation, J.T., M.K. and I.S.; writing—original draft preparation, J.Ł. and J.K.; writing—review and editing, J.K. and L.S.; visualization, J.Ł., M.W. ´ and I.S.; supervision, L.S. and K.G.; project administration, L. ´ S.; funding acquisition, L. ´ S. All authors ´ have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Military University of Technology, grand number: 22- 757/2022.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
