PSI - Issue 68

Rahul Singh et al. / Procedia Structural Integrity 68 (2025) 715–721 Rahul Singh et.al / Structural Integrity Procedia 00 (2025) 000–000

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Fig 3: SEM micrographs showing the crack propagation profile of the specimens tested at 25 °C. The orange arrow indicates the direction of crack propagation.

Fig 3, shows a stitched SEM micrograph of the fracture surface, beginning at the notch and extending along the crack propagation path. The fracture exhibited entirely brittle behavior, with cleavage facets of different sizes that correspond to the nodule size. This indicates that nodule size is a key microstructural factor influencing impact loading at room temperature. Nodules are regions where the ferrite misorientation is less than 13°.

(a)

(b)

(c)

Fig 4 : (a) SEM micrograph of fracture surface (b) SEM micrograph of the section perpendicular to the fracture surface (c) SEM micrograph of the region indicated in orange rectangle in (b). The orange arrow indicates the direction of crack propagation.

Fig 4 (a), shows a SEM micrograph of the fracture surface, it reveals a complete brittle fracture with cleavage-like facets. Fig 4 (b), the SEM micrograph of the crack propagation profile was taken for a section perpendicular to the fracture surface. The crack traverses through the pearlitic microstructure by slightly bending the cementite, as illustrated in Fig 4 (c) marked by an orange circle.

4. Conclusions

• Bulk nano-structured pearlitic steel with interlamellar spacing of 57.2 ± 2.3 nm was manufactured by isothermal transformation at 550 ° C having higher Mn content. • The impact energy absorbed for the Charpy test was found to be 5 ± 0.3 J, which was almost double of the data available for nano-pearlitic steels. • Fractography revealed that nodule size is the microstructure parameter governing the impact loading at room temperature. • Cementite shows mild bending even at room temperature.