Page 55 - ESAM-1-1

Engineering Science in
Additive Manufacturing Additive manufacturing of EH36 steels

but the optimization of scanning strategies and process to its localized heat input and rapid cooling rates, which
parameters is still required to enhance interlayer bonding. necessitate meticulous optimization of process parameters.
DED-Arc experiences the fewest lack of fusion defects due DED-LB, with its larger melt pools and slower cooling
to its larger melt pools and slower cooling rates, which rates, exhibits reduced porosity and residual stresses but
promote better interlayer bonding. However, improper remains susceptible to a lack of fusion and inclusions when
wire feed rates or excessive interpass cooling can still lead feedstock or scanning strategies are suboptimal. DED-Arc
to incomplete fusion at layer interfaces. 68 demonstrates the lowest susceptibility to most defects due

Inclusions, or foreign particles trapped within the to its continuous wire feed and gradual cooling, although
material, are frequently observed in AMed components occasional elongated pores and inclusions may form with
due to feedstock impurities or process inconsistencies. In improper shielding or feed conditions.
PBF-LB, inclusions may result from powder contamination 3.3. Mechanical properties of AMed EH36 steel
or unoptimized scanning strategies. 69,70 An elongated oxide
inclusion, primarily composed of Mn-rich oxides, was PBF-LB fabricated EH36 steel primarily features a
identified within the lack of fusion regions, accompanied martensitic matrix with small amounts of retained
by partial debonding at the melt pool boundary. These austenite, attributed to the rapid cooling rates during
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inclusions disrupt material homogeneity, thus lowering fabrication. This fine microstructure offers higher strength
ductility and increasing the brittleness of the as-print but lower ductility compared to conventional EH36 steel,
components. DED-LB is also susceptible to inclusions as listed in Table 3, where testing direction refers to the
due to the use of powder feedstock and shielding gas, pulling direction relative to the build plane. DED-LB
particularly when the powder has surface oxidation or exhibits superior ductility, with elongation exceeding 28%
residual contaminants. The presence of inclusions, in the XY direction and 26% in the Z direction. In contrast,
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formed due to a trace amount of oxygen leading to metal DED-Arc achieves the highest elongation of 35% in the XY
oxide formation, acts as crack initiation sites, resulting in direction but exhibits lower ultimate tensile strength (UTS)
a defect-driven fatigue failure mode. 30,32 Once embedded and significant anisotropy, with elongation dropping to
within the matrix, these inclusion particles serve as just 12% in the Z direction. The formation of metastable
nucleation sites for microcracks under applied stress, micro-constituents along the melt pool boundaries
significantly compromising the fatigue performance of the locally increases hardness and brittleness, whereas grain
material. coarsening in the HAZ causes slight localized softening.
This inhomogeneous microstructure contributes to the
Residual stress-induced cracking is also a type of anisotropic ductility observed in the DED-Arc fabricated
prominent defect in AMed EH36 components, originating parts.
primarily from steep thermal gradients during rapid
solidification and cooling. In PBF-LB, high cooling rates Moreover, the mechanical properties of EH36 steel
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(10³ – 10⁶ K/s) associated with laser melting processes fabricated through PBF-LB are significantly influenced
lead to substantial residual stresses and martensitic by scanning speed and hatch spacing. Lower scanning
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transformations, causing embrittlement and cracking speeds (e.g., 100 mm/s) provide higher yield strength and
susceptibility if residual stresses are not adequately managed UTS, approaching 875 MPa and 1000 MPa, respectively.
through optimized scanning parameters. 74,75 and substrate In contrast, higher speeds (e.g., 400 mm/s) result in a
pre-heating (around 100°C) Similarly, in DED-LB, severe notable reduction in strength, with UTS dropping to
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residual stresses from rapid heating and cooling cycles around 820 MPa, accompanied by a decline in elongation
necessitate precise control of energy input and interpass from 8.7% to 3.9%. Optimizing the hatch spacing (e.g.,
temperatures to minimize crack formation. 49,76 For DED- 0.11 mm) improves energy input and melt pool uniformity,
Arc, though featuring comparatively lower cooling rates, enhancing densification and mechanical properties. Larger
residual stresses can still trigger cracking due to thermal hatch spacings, however, increase the risk of defects due to
gradients and inconsistent heat input, highlighting the insufficient energy input.
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importance of dwell-time management between layer
depositions to keep the interpose temperatures below 4. Optimization of tensile properties of
165°C. 31 AMed EH36 steel through heat treatment
Table 2 compares the distinct defect profiles of PBF-LB, Heat treatment plays a pivotal role in tailoring the
DED-LB, and DED-Arc for EH36 steel, emphasizing the microstructure and enhancing the mechanical properties
strengths and challenges of each technique. PBF-LB is prone of AMed EH36 steel. Due to the high cooling rates achieved
to gas porosity, lack of fusion, and high residual stresses due during the PBF-LB and DED-LB processes, the obtained

Volume 1 Issue 1 (2025) 6 doi: 10.36922/ESAM025060005