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

Table 2. Comparison of the measured chemical composition controlled test cycle. To make the hardness (and non-
(wt.%) between the maraging steel powder and the destructive strength) assessment, 10 different hardness
fabricated Tool Steel 1.2709‑A LMF (TRUMPF) part, measurements were taken at random locations on both
including surface averages both with and without the surfaces; for that purpose, the bottom surface, originally
presence of extraneous Ni‑Fe‑Ti intermetallic compounds fused and cut from the substrate plate, was polished
Ni Co Mo Ti Fe and the top surface was left as built. In addition, a heat
Powder 14.39 10.73 4.00 1.36 balance treatment and age-hardening of 6 hours at 500°C was
performed on a similar cut part, followed by another
Part surface (with IC) 12.81 7.40 3.38 8.87 balance
hardness measurement on the same surfaces.
Part surface (without IC) 14.64 7.60 3.21 1.13 balance
Tensile strength and hardness are both indicative of a
metal’s resistance to plastic deformation and are therefore
chemical composition closely matches that of the original approximately proportional. In metal testing, indentation
powder, as shown in Table 2. hardness exhibits a linear correlation with tensile strength,
allowing for the non-destructive estimation of a material’s
3.5. Mechanical properties: Hardness (and strength)
tensile properties. A straightforward conversion from
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The Rockwell hardness of a material was determined by Rockwell hardness (HRC) to Brinell hardness (HB) can
applying a mild force followed by a major load. The zero be achieved using the recommended formulas derived
position was established by the minor load. The primary load elsewhere, given by:
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was imposed and subsequently withdrawn while the small HB = 8.570 · HRC + 27.6 (for 31 < HRC < 40), (I)
load was maintained. The depth of penetration relative to
the zero datum was determined using a dial, with a harder HB = 17.515 · HRC − 401 (for 51 < HRC < 60). (II)
material yielding a lower reading. That is, the penetration Similarly, according to the conversion tables provided by
depth is inversely related to the hardness. The primary ASTM, the corresponding converted Vickers hardness
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advantage of Rockwell hardness is that it displays hardness (HV) may be determined.
values immediately, eliminating the need for laborious
computations associated with other hardness measuring All the measured and converted hardness values
systems. It is frequently utilized in the fields of engineering obtained are presented in Table 3. As expected, the heat
and metallurgy. The commercial success of this method treatment results in higher hardness values due to the age-
is attributed to its speed, dependability, durability, high hardening process. The obtained HRC values fall within the
resolution, and the ability to measure very small indentation expected and reported range: 33–37 HRC in the as-built
areas. This is particularly advantageous for analyzing and untreated state, and 50–54 HRC in the age-hardened
small samples, as in this study where we investigated the state. For a confidence interval of 95%, the hardness
mechanical properties of a 3D-printed maraging steel deviation from the mean (error) is very small (<1%) for
measurements performed on a prepared and polished
demonstration part. The method allows for non-destructive surface in the non-heat-treated case. This indicates that the
testing, enabling direct inspection of local properties without mechanical properties of the part are quite homogeneous
damaging the part. Traditional methods, such as standard
tensile testing, would require extracting material samples, and that measuring directly on the as-built surface increases
which is not feasible for this application and investigation. the error to approximately <4%, leading to underestimated
hardness (and strength) values. For the heat-treated case,
Of the various different Rockwell hardness scales, the the deviation in measurements on the polished surface is
“B” and “C” scales are the most often used. Both express also small, but conversely, perhaps due to a reduction in
hardness as a dimensionless arbitrary number. For the ductility from the age-hardening and increased sensitivity
C scale used here, typically used in steel, hard cast irons, of the results with pre-load of the indenter at the onset
titanium, and other materials harder than 100 HRB, it uses of the test, the unpolished surface results overestimate
a spheroconical diamond (Brale) indenter, made with a the true values. Nonetheless, the error with all methods
conical diamond of 120° angle and a tip radius of 0.2 mm remains small and acceptable, providing good mechanical
(nominal dimensions), which is used for the hardest properties estimation for engineering purposes.
materials, with a preload of 10 kgf and major load of 150 kgf.
From the determined values of the hardness employing
In this study, the hardness of the cut sample from the the different values obtained for the different scales, both
3D-printed maraging steel part was evaluated on both the the yield (YS) and tensile strength (TS) can be estimated
top and bottom surfaces using an EmcoTest DuraVision with different approaches, as presented in Table 4. The first
20G5 hardness tester, equipped with an electronically approach considers the approximate interrelationships

Volume 4 Issue 2 (2025) 10 doi: 10.36922/MSAM025040002