Page 57 - ESAM-1-1

Engineering Science in
Additive Manufacturing Additive manufacturing of EH36 steels

Table 4. Summary of heat‑treated mechanical properties of AMed EH36 steel
AM Heat treatment (°C) Yield stress (MPa) UTS (MPa) Elongation (%) Testing direction Heat treatment profile References
PBF-LB 205 972 1026 3.6 XY Chamber cooled to room 33
315 901 895 2.2 temperature
425 952 993 4
540 934 977 5.8
650 670 736 9.8
800 341 448 29
DED-LB 500 574.9±16.0 676.2±8.3 39.8±0.2 XY Heated to 910°C, 78
water-cooled, then
heat-treated to 500°C
before air cooling
DED-Arc 800 NA 447±11 34±1 XY Heated to 1000°C, 31
455±13 30±2 Z furnace-cooled, then
reheated to 800°C before
air cooling
551±16 35±1 XY Heated to 1000°C,
555±17 33±1 Z furnace-cooled, then
reheated to 800°C before
water quenching
Abbreviations: AM: Additive manufacturing; DED-Arc: Direct energy deposition using electric arc; DED-LB: Direct energy deposition using laser
beam; PBF-LB: Powder bed fusion using laser beam.

acicular ferrite and the strength of martensite. These results irregularity of the pores and extend of lack of fusion
emphasize the critical role of cooling rates in determining gradually diminish as the scanning speed decreases, where
microstructural outcomes and mechanical performance. SS100 demonstrates the lowest porosity with only minimal
lack of fusion. In contrast, SS100 demonstrates the lowest
5. Fatigue properties of AMed EH36 steel porosity but a minimal lack of fusion. The densification
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The fatigue properties of AMed EH36 steel are of critical levels were found to be 99%, 98%, 94%, 94%, and 91% for
importance for applications in marine and offshore SS100, SS200, SS250, SS300, and SS400, respectively. It was
structures subjected to cyclic loading. The unique clearly observed that the density would decrease steadily
microstructures and defect profiles associated with the with increasing scanning speed.
AM process would also influence fatigue performance. Fatigue crack initiation primarily occurred at stress
Understanding and optimizing these factors are essential concentrators, such as unmelted powders with elongated
for ensuring the long-term reliability of AMed EH36 steel narrow lack of fusion and pores ranging from 5 to 50 µm
components. in diameter, highlighting the importance of minimizing

AM introduces process-specific features, such as fine porosity to enhance fatigue performance. Sample SS100
microstructures in PBF-LB and coarser grains in DED-LB, exhibited the highest fatigue limit of approximately 180
that dictate fatigue behavior. For example, Wang et al. MPa due to its superior densification. SS300, fabricated
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managed to reduce porosity and improve densification to at the highest scanning speed of 300 mm/s with a hatch
enhance the fatigue life of AMed EH36 steel by optimizing spacing of 0.12 mm, showed the lowest fatigue limit of
the laser scanning speed. The effect of laser scanning 104 MPa due to increased porosity and microstructural
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speed on the fatigue properties of EH36 steel was analyzed irregularities. The optimized hatch spacing for maximum
across five samples: SS100, SS200, SS250, SS300, and performance was determined to be around 0.08 mm,
SS400. The last three digits of each sample name indicate with a scanning speed of 100 mm/s, highlighting the
the corresponding laser scanning speed in mm/s. Fatigue importance of balancing scanning speed and hatch spacing
testing was also conducted at a loading frequency of 10 life to achieve superior fatigue properties. In contrast, the
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cycles. The vertical cross-section of initial polished samples highest-density sample (SS100) exhibited fatigue fracture
reveals distinct differences in porosity across scanning initiation at a triple-point crack site characterized by slip
speeds. SS400 exhibits the highest porosity, characterized markings forming extrusions near a pore. These geometric
by irregularly shaped pores and lack of fusion. The discontinuities at the surface acted as stress risers,

Volume 1 Issue 1 (2025) 8 doi: 10.36922/ESAM025060005