Page 84 - MSAM-4-1

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

face-centered cubic iron phase peak (2θ = 43.1°) in the change in grain shape from columnar to equiaxed when 5
powder probably indicates the presence of a small amount wt.% yttrium was added to 304 L steel. A decrease in grain
26
of residual austenite. However, after SLM, this peak length has also been observed in other research. The
intensity undergoes a notable reduction. This is probably application of platform pre-heating results in a decrease
due to the lower cooling rates of SLM compared to gas in the temperature gradient, consequently leading to the
atomization. This observation signifies a modification in creation of more favorable conditions for epitaxial growth
the material’s structural configuration, probably related to during the transition between layers and the formation of
the redistribution of chromium and carbon in the process. elongated grains along the building direction. The sample
The evident broadening of the peaks of the material after obtained by SLM with pre-heating is characterized by an
heat treatment signifies a reduction in grain size, which average grain length of 133.2 ± 55 μm and an average width
was further supported by the microstructural observations of 21.1 ± 8 μm. After heat treatment, the material became
presented in Figure 6. partially recrystallized and the shape of the grains was
almost equiaxed. The grain size reduction in heat-treated
The microstructure of the samples after SLM with pre- samples, as compared to materials before heat treatment,
heating is characterized by columnar grains oriented along is shown in Figure 7. The average grain length and width
the building direction, as shown in Figure 6A and B, which decreased to 39.9 ± 11 μm and 18.5 ± 7 μm, respectively.
are typical for this group of materials in SLM production. The structure obtained after heat treatment became
17
The appearance of melt pools and heat-affected zones, more similar to the structure of materials fabricated by
typically observed after SLM, is not strongly evident in conventional manufacturing methods. Besides, the
36
our samples. However, the addition of Y O decreased formation of small equiaxed grains was also observed. Y O
37
2
3
3
2
the grain length compared to the base material. The base probably act as crystallizing centers during heterogeneous
38
steel produced by SLM without pre-heating exhibited nucleation, resulting in smaller equiaxed grains.
an average grain length of 156 μm and an average grain
width of 30 μm. After the incorporation of 0.25 wt.% 3.4. Mechanical properties
38
Y O , the average grain length decreased to 112.0 ± 20 μm, Finally, the tensile properties of the samples produced by
2
3
and the average grain width increased to 57.0 ± 11 μm. SLM with and without subsequent heat treatment were
In a previous study, Ghayoor et al. reported a significant assessed. The results of tensile testing at room and at
39
A B C

Figure 6. Microstructure of samples: (A) SLM sample without pre-heating, (B) SLM sample pre-heating at 300°C, and (C) SLM sample after heat treatment. ×200
Abbreviation: SLM: Selective laser melting
A B

Figure 7. Stress strain curves for samples after SLM without and with heat treatment tested at: 20°C (A) and 720°C (B).
Abbreviations: HT: Heat treatment; SLM: Selective laser melting

Volume 4 Issue 1 (2025) 7 doi: 10.36922/MSAM025060004