L-PBF Processing of Low Alloy Steels

William Hearn

Chalmers University of Technology – CAM2

Abstract

One of the largest limitations with metal-based additive manufacturing (AM) is the lack of approved materials. This is especially true for ferrous alloys, as currently only highly alloyed steels such as stainless, maraging or tool steels have been approved for AM. A group of ferrous alloys that have not received much attention are low alloy steels, which provide good strength and toughness without the requirement of many alloying additions. However, low alloy steels can be susceptible to cracking defects due to the residual stresses that form during AM combined with the high hardenability of the material. This work explored the laser powder-bed fusion (L-PBF) production of four low alloy steels (4130, 4140, 4340 and 8620). Processing windows could be established for each alloy that produced high density (>99.8%), defect-free specimens. Outside of these processing windows the formation of porosity and cracking defects could be identified, with said defects being dependent upon the volumetric energy density (VED) and the alloying carbon content. Low VED specimens displayed lack of fusion and cracking defects, while high VED specimens displayed the combined prescence of gas and keyhole porosity. As for the alloy composition, increasing the carbon content increased the cracking susceptibility. However, this issue could be mitigated by increasing the VED.