Synergistic improvement of strength and ductility via doping cerium into PH13–8Mo stainless steel by laser powder bed fusion

Abstract

In this study, the PH13–8Mo stainless steel parts doped without and with cerium (Ce) were fabricated via laser powder bed fusion followed by post-heat treatment, and systematically compared in terms of microstructure, phase constituent, and tensile properties. The comparative results show that doping Ce-modified grains with the equiaxed morphology and finer size, increased the mechanical stability of austenite, and enhanced the sphericity of oxide inclusion in the resultant PH13–8Mo. Additionally, the coherency between the newly-formed CeAlO3 inclusion and matrix was effectively improved after doping Ce, as compared to the original aluminum oxide inclusion without doping Ce. The resultant PH13–8Mo parts doped with Ce yielded an ultimate tensile strength of 1446 ± 20 MPa with a fracture elongation of 16.0% ± 1.5%, for the first time meeting the AMS 5629E H1000 standard for the PH13–8Mo made by additive manufacturing (AM). The enhanced strength results from the strengthening effects of nanoscale precipitation (inclusion) and grain refining. Meanwhile, the ductilizing mechanism can be attributed to the enhanced inclusion sphericity and ameliorative coherency between the inclusion and matrix, and improved misorientation angle of grain boundary owing to the modification by Ce, which efficiently reduced the stress concentration and enhanced cracking resistance during deformation. Therefore, doping rare earth elements presents a promising pathway to synergistically improve the strength and ductility of stainless steels by AM.