Page 84 - MSAM-4-2

Materials Science in Additive Manufacturing Quality of a 3D-printed steel part

is irrelevant. After annealing, the low-carbon martensite
formed is relatively soft (about 35 HRC). There are only
very slight dimensional changes during age-hardening.
As a result, relatively complex shapes can be machined
or 3D-printed in the soft state and then hardened with
minimal distortion. This material has excellent weldability
and its fracture toughness is significantly higher than that
of conventional high-strength steels. This property in
particular has resulted in the widespread use of maraging
steels in a variety of demanding applications. 45,46
The 1.2709 maraging steel is a pre-alloyed, ultra-high-
strength steel available in powder form. Its composition
aligns with the U.S. classification 18% Ni Maraging Figure 3. 3D-printed studied maraging steel part as built inside in the
300, the European designation 1.2709, and the German machine and connected to the substrate plate (top); final part and cut
standard X3NiCoMoTi 18-9-5. Maraging steels are material sample (bottom)
known for their exceptional strength-to-toughness ratio
while maintaining ductility, weldability, and dimensional height of 14 mm. Thin fins and cylinders, each 6 mm in
stability throughout the aging process. Most maraging height, are extruded above an 8 mm base plane. The part
steel grades exhibit martensite start temperatures between was 3D-printed using a Truprint 1000 machine with a layer
200°C and 300°C, achieving a fully martensitic structure thickness of 20 μm, a laser scanning speed of 600 mm/s,
at room temperature. Consequently, retained austenite is power of 100 W and beam diameter of 55 μm, which
typically not a concern in these alloys, eliminating the need were optimized for maraging steel, with a printing time of
for refrigeration treatments before aging. The resulting around 6 hours. As illustrated in Figure 3 (top images), the
martensite is a low-carbon, body-centered cubic (BCC) part was printed within the central cylinder and remained
lath structure characterized by a high dislocation density fused to the steel substrate plate upon completion.
and the absence of twinning. In its as-built and untreated A Struers Accutom-2 precision cutting machine, equipped
state, 1.2709 maraging steel exhibits a yield strength (YS) with a diamond cut-off wheel, was used to separate the
and tensile strength (TS) of approximately 1000 ± 100 part from the substrate plate and extract a material sample
MPa and 1100 ± 100 MPa, respectively, with an elongation (indicated by the red line in the bottom image) for detailed
of 8 ± 3% and a hardness of 33–37 HRC. After aging quality analysis and inspection.
treatment, these properties improve significantly, reaching 3. Part characterization and quality analysis
1900 ± 100 MPa for YS, 1950 ± 100 MPa for TS, 2 ± 1%
elongation, and a hardness of 50–54 HRC (cf. ). These 3.1. Feedstock powder material characterization
47
enhanced mechanical characteristics make maraging steel The feedstock powder used for fabricating the
a highly suitable material for AM applications, including demonstration part, designated as Tool Steel 1.2709-A
automotive components such as gears, drive shafts, springs, LMF, was supplied by TRUMPF. To ensure powder quality,
and heavy-duty transmissions; aerospace applications analyses of particle size distribution, morphology, and
such as rocket and missile skins; sports equipment such as chemical composition were conducted. The morphology
fencing blades, bicycle frames, and golf club heads; as well and chemical composition were examined using a Hitachi
as machinery and tooling across various industries. The SU1510EM Scanning Electron Microscope (SEM) (Hitachi,
readers are referred to a few publications 43,45,46,48 for further Japan), while particle size distribution was assessed with
technical insight into maraging steels technology. a Malvern MS3000 laser diffraction analyzer (Malvern
Instruments, United Kingdom), providing fast, accurate,
2.3. 3D-printed part and material sample
and reliable measurements. Figure 4 presents the particle
The 3D-printed component examined in this study, morphology, revealing predominantly spherical particles
depicted in Figure 3, is a demonstration piece fabricated with minimal agglomeration and surface irregularities,
using maraging steel feedstock powder, specifically the indicative of high-quality powder with a low risk of
Tool Steel 1.2709-A LMF grade supplied by TRUMPF. The defects. A high-magnification (3000×) image of a particle
hollow part contains several intricate geometrical features surface is also displayed in Figure 5. Chemical composition
designed to test the limits of AM capabilities. Its overall analysis was performed using an SEM equipped with
projected dimensions fit within a rectangle measuring 69 a Bruker Quantax 200 detector for Energy-Dispersive
× 70 mm and a circle with diameter of 90 mm, with a total X-ray Spectroscopy (Bruker Corporation, United States).

Volume 4 Issue 2 (2025) 6 doi: 10.36922/MSAM025040002