Page 56 - ESAM-1-1

Engineering Science in
Additive Manufacturing Additive manufacturing of EH36 steels

Table 2. Comparison of different AM techniques for the fabrication of EH36 steel
Defect type PBF‑LB DED‑LB DED‑Arc
Gas porosity High; due to rapid cooling and improper Moderate; larger melt pools allow better Low; wire feed minimizes gas
inert gas flow; small spherical pores gas escape; localized porosity if powder entrapment, but elongated pores can
feed is inconsistent form with poor shielding gas
Lack of fusion Common; due to low energy density or poor Occurs with suboptimal laser power or Rare; large melt pool improves
layer bonding; irregular voids powder feed; voids at layer interfaces bonding, but improper wire feed can
cause interlayer delamination
Inclusion Caused by powder contamination or Related to surface oxidation or residual Less frequent; clean wire feed reduces
unoptimized scanning; non-metallic contaminants in powder feedstock; cracks occurrence, but inclusions may form
particles embedded in the matrix initiate from voids with inclusions with inadequate shielding
Residual Common; caused by steep thermal gradients Common; severe residual stresses due to Occurs due to cyclic heating/cooling
stress-induced due to rapid solidification and cooling; rapid heating and cooling cycles and thermal accumulation
cracking
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.

Table 3. Summary of the microhardness and tensile properties of AMed EH36 steel
Process Scanning speed (mm/s) YS (MPa) UTS (MPa) Elongation (%) Hardness (Hv 0.05 ) Testing direction References
PBF-LB 100 874±111 971±43 8.7±1.8 288±25 XY 29,34
200 867±8 921±28 6.3±1.4 334±12 XY
250 845±24 891±38 5.2±0.95 345±15 XY
300 809±15 855±16 4.3±0.9 345±21 XY
400 751±39 808±50 3.6±0.4 338±15 XY
DED-LB 20 612±21 708±10.4 28±0.9 220±11.9* XY 30
927.1±13 970±10.9 24.7±0.5 297.1±20** XY 78
DED-Arc 0.5 NA 497±18 35±2 160±7* XY 31
DED-LB 20 578±12.1 644±6.8 26±2.5 281.5±18.3* Z 30
DED-Arc 5 NA 504±21 12±3 160±7* Z 31
Conventional rolling - 500 572 22 185*** - 79
ASTM - 355 490 – 620 20 - - 80
Note: *Hv ; **Hv ; ***Hv .
10
0.2
0.3
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; UTS: Ultimate tensile strength; YS: Yield strength.
microstructure is usually martensitic or bainitic, which EH36 steel. Air-cooled samples exhibited a predominantly
gives high strength but poor ductility. The mechanical uniformed ferritic-pearlitic microstructure with coarser
properties can be further improved by performing grains, where the pearlite phase is formed along the grain
post-fabrication heat treatments such as annealing or boundaries, as well as the triple junction of polygonal
normalizing to bring about phase transformations that ferrite grains. This homogenized microstructure enhanced
favor the formation of ferrite and pearlite for improved dimensional stability and reduced susceptibility to crack
ductility. Furthermore, these treatments also render stress initiation but slightly lowered tensile properties. Samples
relief and greater microstructural uniformity. As presented subjected to water quenching would exhibit a dual-phase
in Table 4, Wu et al. reported that heat treatment at 800°C microstructure composed of polygonal ferrite and acicular
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increased the elongation of PBF-LB fabricated EH36 steel ferrite, where the acicular ferrite nucleated along the grain
from 12% to 29%; such elongation of the heat-treated boundaries of the polygonal ferrite. Similarly, DED-LB
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sample eventually exceeded the ASTM standard, which is demonstrated a similar trend after air-cooling, consisting
20%. of polygonal ferrite and intergranular pearlite. This
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Vahedi Nemani et al. investigated the effects of air microstructure achieved a favorable combination of high
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cooling and water quenching on DED-Arc fabricated strength and toughness, attributed to the toughness of

Volume 1 Issue 1 (2025) 7 doi: 10.36922/ESAM025060005