Effects of oxygen content on microstructure and mechanical properties of 18Ni300 maraging steel manufactured by laser directed energy deposition

Compared to conventional material processing technologies, laser directed energy deposition (LDED) belonging to additive manufacturing (AM) has many advantages and enormous commercial potential. However, the effect of external factors on the deposition process has not been completely revealed such as the oxygen content in the manufacturing environment. 18Ni300 as maraging steel has excellent mechanical performance, but oxidation inside parts could induce metallurgical defects like inclusion or cracks and impair the service life of parts. Therefore, this paper focuses on the microstructure and mechanical properties of 18Ni300 maraging steel fabricated by LDED under different oxygen contents. The control of oxygen content in the environment was achieved by changing the argon content. Experimental results indicated that the forming accuracy of specimens and process stability were effectively improved at both 500 ppm and 50 ppm oxygen contents. The width of equiaxed grain region, grain growth orientation and primary dendritic arm spacing were significantly affected by gaseous environment. In the low oxygen content group, higher microhardness values were obtained due to the effect that similar to heat treatment. The ultimate tensile strength of samples reached to 908 MPa under 50 ppm oxygen content, which exceeded the tensile strength of wrought components.