Abstract
The present study examines the processability of Fe-C alloys, with carbon contents up to 1.1 wt%, when using laser based powder bed fusion (LB-PBF). Analysis of specimen cross-sections revealed that lack of fusion porosity was prominent in specimens produced at low volumetric energy density (VED), while keyhole porosity was prominent in specimens produced at high VED. The formation of porosity was also influenced by the carbon content, where increasing the carbon content reduced lack of fusion porosity, while simultaneously increasing the susceptibility to form keyhole porosity. These trends were related to an improved wettability, viscosity, and flow of the melt pool as well an increased melt pool depth as the carbon content increased. Cold cracking defects were also observed in Fe-C alloys that had an as-built hardness ≥425 HV. Reducing the carbon content below 0.75 wt% and increasing the VED, which improved the intrinsic heat treatment during LB-PBF, were found to be effective mitigation strategies to avoid cold cracking defects. Based upon these results, a process window for the Fe-C system was established that produces high density (>99.8%), defect-free specimens via LB-PBF without the requirement of build plate preheating.
Highlights
One of the greatest limitations of laser based powder bed fusion (LB-PBF) is its restricted materials portfolio
- Analysis of specimen porosity revealed that at low volumetric energy density (VED) there was the noticeable presence of lack of fusion porosity, while at high VED there was a noticeable presence of keyhole porosity
- Increasing the carbon content limited the formation of lack of fusion porosity at low VED, while increasing the susceptibility to form keyhole porosity
Summary
One of the greatest limitations of laser based powder bed fusion (LB-PBF) is its restricted materials portfolio. This is apparent when examining ferrous alloys in LB-PBF, as they remain limited to alloys with low carbon content (e.g., stainless and maraging steels). These approved ferrous alloys constitute a small portion of what is used in industry and exclude carbon-containing ferrous alloys like low-alloy steels and tool steels, which provide the high strength, toughness, and wear resistance required for structural and tooling applications To expand the materials portfolio of LB-PBF, the development of these alloys would be of great benefit
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