Page 53 - ESAM-1-1

Engineering Science in
Additive Manufacturing Additive manufacturing of EH36 steels

distribution (PSD) range present good flowability and layer feedstock properties, processing characteristics, and
uniformity, as the likelihood of powder agglomeration typical applications. This comparison summarizes the
is significantly reduced to achieve efficient packing. Wu advantages and constraints of each method. PBF-LB offers
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et al. used EH36 powder with a PSD of 28 – 50 µm, a tapped superior precision and surface quality, DED-LB provides
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density of 5.1 g/cc, and a Hall flow rate of 27.6 s/50 g. These greater scalability and process efficiency, while DED-Arc
specifications were chosen to enhance powder flowability is recognized for its cost-effectiveness and high material
and ensure optimal packing density within the powder bed deposition rates.
for PBF-LB. This optimized size range enhances powder
spreading, reduces inter-particle friction, and minimizes 3. Microstructure evolution, defects, and
defects, such as incomplete melting, during the layer-by-layer mechanical properties of AMed EH36 steel
fabrication process. Unlike PBF-LB, which requires highly 3.1. Melt pool and microstructural characteristics of
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flowable powders with narrow particle size distributions, AMed EH36 steel
DED-LB can utilize powders with lower flowability due to
its direct feeding mechanism. The EH36 powder designed The melt pool dimensions and heat-affected zone (HAZ)
for PBF-LB can be directly used in DED-LB. Meanwhile, characteristics are fundamental to understanding the
powders produced by gas atomization with particle sizes microstructural evolution and mechanical performance
ranging from 45 to 90 µm and tapped density of 5 g/cc, of AMed EH36 steel components. Each AM method,
are also suitable for DED-LB. Such flexibility of powder including PBF-LB, DED-LB, and DED-Arc, employs
feedstock offers high deposition efficiency while relaxing distinct thermal input strategies and cooling rates, resulting
the constraints associated with feedstock preparation. 28,35 in unique melt pool sizes and HAZ profiles. These variations
The broader PSD range accepted by DED-LB facilitates directly influence grain morphology, phase distribution,
the use of cost-effective powders while still meeting the and residual stresses in the fabricated material. PBF-LB
mechanical and structural demands of marine and offshore process creates small melt pools, typically ranging from 50
applications. The chemical composition (wt.%) of EH36 to 100 µm in depth and 100 – 200 µm in width, due to
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steel powder, typically consisting of C (0.18), Si (0.1 – 0.5), its localized energy input and rapid cooling rates. These
Mn (0.9 – 1.6), P (0.035), S (0.035), Cr (0.2), Mo (0.08), Ni compact melt pools contain elongated cellular-dendritic
(0.4), V (0.05 – 0.1), Cu (0.35), Nb (0.02 – 0.05), Ti (0.02), grains, approximately 1 ± 0.5 µm, with finer acicular
grains with a size of 1 – 2 µm and equiaxed grains around
and Fe (balance), significantly influences its mechanical 5 – 6 µm near the center of the melt pool. The high cooling
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properties and suitability for AM processes, contributing rate, ranging from 10⁵ to 10⁶ K/s, ensures that the thermal
to its high strength, toughness, and weldability critical for effects are confined to the immediate vicinity of the melt
marine and offshore applications. Compared to PBF-LB pool, resulting in refined microstructures and narrow
and DED-LB, DED-Arc uses wire feedstock that is easier HAZs. The rapid solidification of PBF-LB leads to the
to handle and eliminates the need for stringent powder micro-segregation of elements such as carbon, manganese,
flowability requirements. 58 and other alloying elements at the grain boundaries. This
Table 1 provides a comparison of the three AM segregation could stabilize the austenite phase and suppress
techniques for EH36 steel fabrication, focusing on their the martensitic transformation, thereby increasing the

Table 1. Comparison of different AM techniques for the fabrication of EH36 steel 59

Features PBF‑LB DED‑LB DED‑Arc
Feedstock Powder Powder Wire
Feedstock PSD Narrow Wide -
Feedstock rate Low Moderate to high High
Power moderate High Very high
Scanning speed High Moderate Low
Hatch spacing Low Moderate High
Scalability Normally small parts, limited by chamber size Suitable for medium to large parts Highly scalable, large parts
Precision High Moderate Low
Applications Complex geometries, precise and intricate parts Structural components, repairs Large-scale structures (e.g., ship hulls)
Abbreviations: DED-Arc: Direct energy deposition using electric arc; DED-LB: Direct energy deposition using laser beam; PBF-LB: Powder bed fusion
using laser beam; PSD: Particle size distribution.

Volume 1 Issue 1 (2025) 4 doi: 10.36922/ESAM025060005