Fabrication of a low alloy ultra-high strength (>1500 MPa yield) steel using powder bed fusion additive manufacturing

In this work, a low alloy ultra-high strength steel is fabricated using powder bed fusion (PBF) additive manufacturing (AM). PBF process parameters and scan strategy to manufacture this ferrous alloy from powder form to fully dense part were successfully developed. Specifically, a process map for laser processing of this material was determined by observing the shape and regularity of the melt pool as a function of laser powers and laser scan speeds using laser profilometry. In addition to processing, mechanical testing and metallurgical examinations using 2D optical and electron microscopy along with the 3D examination of the defect (porosity) structure using micro X-ray computed tomography have been carried out. Since the total volume of detectable pores found throughout the material was negligible, the AM fabrication of the steel is regarded as successful. AM samples were found to have a quasi-static yield strength greater than 1500 MPa, an ultimate strength exceeding 1800 MPa, and 20% elongation in the as-built condition. Significantly, these mechanical properties are superior over the same material in the as-cast conditions and are comparable to those of the wrought form of the material. Details pertaining to processing along with the characterization and testing results are presented and discussed in this paper.