Page 100 - MSAM-4-2

Materials Science in Additive Manufacturing Additively manufactured high carbon steel

Figure 5. X-ray diffraction patterns of as-printed samples annealed at various bainitic transformation temperatures for 3 h
A B A B

C D Figure 7. Optical micrograph of samples annealed at 175°C for (A) 3 h
and (B) 24 h. Bainite etches are indicated in dark shades. Scale bars: 1 mm

or bainite, all of which still possess a large fraction of
austenite available for further transformation in a multi-
step process. First, a matrix consisting of quenched
martensite and bainite could be obtained (Figure 8A). The
E F combination of quenching in LN for 2.5 h, followed by heat
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treatment at 175°C for 1 h, yielded islands of austenite,
along with martensite and bainite adorned with cellular
dendrites. The large, interconnected network of cells
made it challenging to distinguish between martensite
and bainite. Figure 8B displays the microstructure of
the sample solutionized at 1075°C for 1 h, quenched
Figure 6. Optical micrographs of the as-printed sample (A) and annealed in LN for 2.5 h, and then heat treated at 175°C for
2
samples at (B) 125°C for 3 h, 175°C for 3 h (C), 200°C for 3 h (D), 250°C 1 h. The resulting microstructure is, however, a mix of
for 3 h (E), and 300°C for 3 h (F). The bainite etches are denoted as dark austenite, martensite, and bainite, without the cellular
contrasts
network. It is much easier to distinguish between the
different phases in this microstructure. As presented in
increase in the amount of bainite was observed even after Figure 8B, the bainite sheaves, which generally etch dark,
the prolonged isothermal treatment. were observed to have nucleated at the boundary of the
plate martensite and grew across the retained austenite
3.4. Multi-phase high-carbon-bearing steel island. The nucleation of bainite along the γ/α’ interface
It has been demonstrated thus far that the as-printed is preferred, and this mechanism is likely similar to
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microstructure can be solutionized, quenched, and that observed in the quenched and tempered condition
annealed to obtain “cell-free,” quenched martensite presented in Figure 8A.

Volume 4 Issue 2 (2025) 7 doi: 10.36922/MSAM025100011