Laser-based powder bed fusion of 16MnCr5 and resulting material properties

Abstract

Laser-based Powder Bed Fusion (LPBF) has evolved to a manufacturing technology for prototype and small scale production of gears. The case hardening steel 16MnCr5 is typically used and its material properties are well known and understood. However, the resulting material properties following the post-LPBF process sequence such as residual stress annealing, case hardening and hard finishing are widely unknown. This paper presents a study of processing 16MnCr5 with an EOS M270 LPBF-machine reaching 99.5 % relative density and above. The resulting microstructure and hardness of the material is examined. Furthermore, the tensile strength as well as the gear-specific tooth root carrying capacity are studied. The results are compared to a conventionally processed material via continuous casting. It is shown that residual stress annealing widely compensates material anisotropy following the LPBF process. Material hardness in the as-built condition is increased up to 21 % compared to a conventional material. The case hardening behavior shows a difference in the resulting case hardening depth in comparison to conventional material. The residual stresses measured at the surface after the case hardening show compressive stresses. Pulsator tests deliver a stress-cycle (S-N) curve from which the tooth root carrying capacity can be derived.