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Materials Science in Additive Manufacturing SLM of ODS steel: Process and properties

operating (720°C) temperatures are presented in Figure 7
and Table 3. The results of the tests conducted on specimens
produced without pre-heating are not presented. This
decision is due to the presence of a significant number of
cracks in the specimens, which made the tests invalid.

The as-built SLM ODS specimens exhibited a brittle
behavior. At room temperature, fracture occurred at 978
MPa with no evidence of plastic deformation before fracture.
This UTS value was comparable to the values for the similar
ferritic/martensitic ODS steel plates and tubes manufactured
through powder metallurgy (UTS = 991 MPa), but the
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problem was YS and elongation was absent. Following
heat treatment, the mechanical response of the SLM ODS Figure 8. Fracture surfaces of samples after SLM without and with heat
specimens during tensile transition to a ductile mode. The YS treatment after tensile testing at 20°C and 720°C. Magnification: ×100
and UTS achieved were lower than the base steel produced Abbreviation: SLM: Selective laser melting
through powder metallurgy techniques (YS = 525 MPa, UTS
= 711 MPa, ε = 16%). The elongation of the heat-treated Table 3. Tensile properties of specimens fabricated in the
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SLM ODS specimens remained significantly lower than that present work
of the powder metallurgy-derived base material. The findings
revealed the substantial impact of incorporating 0.25 wt.% Condition Temperature, °C YS, MPa UTS, MPa ε, %
Y O on the tensile properties. In a prior investigation of SLM ODS 20 - 978±24 -
2
3
base steel produced by SLM, the maximum tensile strength 720 266±2 272±2 7.7±0.1
was also observed for the specimen after SLM without heat SLM 20 440±14 697±25 8.6±0.2
treatment. The UTS was 567 MPa, aligning with the absence ODS+HT 720 144±8 156±5 29.3±0.3
of plastic characteristics. Consequently, the incorporation
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of Y O resulted in a 72% increase in UTS compared to the Abbreviations: ε: Elongation; HT: Heat treatment; ODS: Oxide
dispersion-strengthened; SLM: Selective laser melting; UTS: Ultimate
3
2
base steel. tensile strength; YS: Yield strength.
The mechanical properties of heat-treated SLM
samples, when tested at elevated temperatures, were not cases, no visible cracks, inclusions, or unmelted powder
very significant. The tensile properties of the material particles were detected.
tested at 720°C after SLM were comparable to those of
base steel obtained by powder metallurgy methods (YS The results of the microhardness measurements
= 279 MPa, UTS = 284 MPa, ε = 25%). However, the supported the conclusions regarding the quenched state
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elongation was much lower. The relatively low ductility of of the material after SLM. The sample produced without
all specimens after SLM can be explained by the quenched pre-heating exhibited a value of microhardness of 441 ±
state and internal stresses. 23 HV. The application of pre-heating was found to result
in a reduction of material internal stresses by decreasing
Fractography was used to study the fracture surfaces of the thermal gradient, thereby leading to a decrease in
the specimens. From Figure 8, it can be observed that the microhardness to 390 ± 20 HV. After heat treatment, a
SLM specimen tested at 20°C exhibited an undeveloped microhardness of 288 ± 26 HV was measured.
fracture surface. The fracture occurred without necking,
and the fracture mode appears to be of an intergranular These results underscore the need for a change in the
nature. The specimen, after heat treatment, featured a more heat treatment mode after SLM. The selected heat treatment
developed fracture surface with a few cleavage platforms mode was found to exert a negative impact on the tensile
and a number of dimples. As the specimen after SLM properties of the material. The results of the study indicated
underwent tensile testing at 720°C, its fracture surface the formation of a quenched structure in as-built material
exhibited a significant increment in the number of dimples and subsequent quenching within the heat treatment did
of a lower size. The fracture character of the specimens is not have a positive effect on the structure. Despite the lower
classified as higher ductility, accompanied by the presence values of average grain length and width, the specimens
of brittle fracture areas. The specimen after SLM and heat after heat treatment exhibited lower UTS values. During
treatment tested at 720°C had dimples and micro-voids, an the heat treatment process, which involves quenching
indication of the ductile nature of the fracture. In all the and high-temperature annealing, a recrystallization

Volume 4 Issue 1 (2025) 8 doi: 10.36922/MSAM025060004