PSI - Issue 68

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

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

Fig. 2. Microstructure evolution of the studied TWIP steel though various FH cycles: EBSD-IQ map the corresponding phase map at 1000 °C/5 s (a,b), 1100 °C/ 5 s (c,d), and (e,f) 1200 °C/ 5 s (e,f), respectively.

The tensile properties of the FH-treated microstructures are presented in Fig. 3. It is evident that the steel subjected to FH at 1000 °C for 5 s exhibited superior mechanical properties, including higher yield strength (YS), 340 MPa, and ultimate tensile strength (UTS), 750 MPa, compared to specimens treated at 1100 °C and 1200 °C, as shown in Fig. 3. This improvement is attributed to grain refinement at 1000 °C, see Fig. 3. Notably, all the grain structures demonstrated high ductility, with elongation exceeding 100%. It is well established that this composition of TWIP steel promotes mechanical twinning as the dominant deformation mechanism during tensile straining. This behavior is attributed to its stacking fault energy (SFE), which falls within the range 18–35 mJ/m2 that favors twin formation (Saeed-Akbari et al., 2009). Detailed microstructural observations of the FH-treated specimen at 1200 °C with a 5 s hold, following tensile testing, are shown in Fig. 4. The image quality (IQ) map in Fig.4(a) reveals varying levels of gray across the grain structure, along with a significant