PSI - Issue 68

Ahmed W. Abdelghany et al. / Procedia Structural Integrity 68 (2025) 520–526 Abdelghany et al. / Structural Integrity Procedia 00 (2025) 000–000

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3. Results and discussion Fig. 1 (c) presents the microstructure of sample A, corresponding to the reference TMCP schedule A. In the right half of the image, the processed microstructure is also shown, where the grain boundaries are clearly delineated by red lines, generated through the image processing software. The analysis provided a comprehensive data on grain size, fraction, and cumulative distribution, as shown in Fig. 1(d), revealing an average grain size of 30 µm for sample A.

Fig. 1. (a) TMCP schedules performed using the Gleeble simulator for the 201LN steel, (b) schematic of the deformed sample after sectioning, indicating the central region selected for microstructural analysis, (c) microstructure of the reference TMCP schedule (sample A), with red lines highlighting the grain boundaries detected through image processing, and (d) corresponding grain size distribution of (c). Fig. 2 (a)-(f) depicts the microstructures resulting from the six distinct two-step uniaxial hot compression schedules (schedules I–VI). In general, the grain size displayed pancaking of grains following the second compression, though traces of partial recrystallization can be seen in some cases, particularly at slow final cooling rate (sample VI) and at higher second-hit deformation temperature (sample VI). The presence of pancaked grain structure was observed in all TMCP schedules, indicating substructure strengthening across all tested conditions, despite the occurrence of dynamic and static recovery. This pancaked grain morphology suggests that the material underwent significant deformation in the no-recrystallization regime, which contributes to enhanced mechanical properties by increasing the dislocation density and improving overall strength (Yamamoto et al., 1993). Due to variations in the grain structures, which include mainly deformed (pancaked) grains along with traces of fine, statically recrystallized grains in some cases, an area−weighted averaging method was employed to calculate the grain size, along with the arithmetic mean grain size. This method employs the following equation: ℎ ( ) = ∑" ! ∙$ ! ∑$ ! (1) where D i is the equivalent circle diameter of an individual grain and A i is the area of the same grain. This approach ensures a more accurate representation of grain size by giving more credence to larger grains, which might significantly influence the mechanical properties of the material.