Issue 78

Z. A. Betti et alii, Fracture and Structural Integrity, 78 (2026) 19-30; DOI: 10.3221/IGF-ESIS.78.02

in a (0.25% CMC) polymer solution, which consists of ferrite, lath tempered martensite, and pearlite phases, with a relatively small grain size of approximately 36 µm. This indicates that this polymer concentration provides a moderate cooling rate that contributes to higher grain growth compared to water quenching. Fig. 1-D represents the samples quenched in a (0.4% CMC) polymer solution. The higher polymer concentration resulted in a lower cooling rate compared to the other cases, allowing for a longer interval, leading to grain growth during the phase transition. The CMC concentration of 0.4% may have formed a layer around the sample, slowing the rate of heat exchange between the quenching medium and the sample, thus slowing the cooling process and leading to greater grain growth. This was clearly reflected in the increased ferrite grain size, reaching its highest recorded value (~59 µm). Overall, these results confirm that the type of quenching medium and its concentration play a crucial role in controlling the cooling rate, which directly impacts the development of the microstructure and grain size, as illustrated in Fig. 1 and Tab. 4.

Figure 1: Microstructure of samples: AR) as-received, A) water quenched, B) 0.1%CMC, C) 0.25% CMC, D) 0.4% CMC.

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