PSI - Issue 68

Atef Hamada et al. / Procedia Structural Integrity 68 (2025) 581–587 Atef Hamada et al/ Structural Integrity Procedia 00 (2025) 000–000

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fraction of Σ3 boundaries, marked by red lines. A notable observation is the presence of several deformed grains that lack Σ3 boundaries, indicating that the TWIP effect is not active in these grains. The corresponding orientation map, shown in Fig. (b), illustrates that grains with a 001 orientation do not facilitate the TWIP mechanism. In contrast, twinning is more prominent in grains oriented along the 111 and 101 planes, as these orientations have low Schmid factors, promoting the formation of Shockley partial dislocations and the intrinsic and extrinsic stacking faults necessary for activating mechanical twinning (Chen et al., 2020; Gazder et al., 2013; Hamada et al., 2022).

Fig. 3. Engineering stress-strain curves of the steel undergone FH cycles at various heating temperatures 1000, 1100, and 1200 °C and 5 s time holding

Fig. 4. Microstructural characteristics of the tensile-strained steel after FH treatment at 1200 °C for 1 second: (a) EBSD-IQ map showing Σ3 boundaries (red lines), and (b) corresponding inverse pole figure (IPF) orientation map. 3. Conclusions This study highlights the effectiveness of fast heating (FH) as an innovative thermal processing technique for refining the microstructure and enhancing the mechanical properties of heavily cold-rolled TWIP steel. The rapid heating rate of 500 °C/s and short heating duration of 5 s applied during FH cycles resulted in fully recrystallized grain structures with varying grain sizes, depending on the heating temperature. 1. For instance, at 1200 °C without holding time, 0 s, a fully recrystallized structure with an average grain size of 20 µm was achieved. In contrast, FH cycle at 1000 °C for 5 s resulted in a finer recrystallized structure with an average grain size of 2.5 µm, while FH at 1100 °C for 5 seconds produced 10 µm grain size.