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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with the help of liquid nitrogen. The sample underwent microstructural analysis using a field emission gun transmission electron microscope (FEG-TEM) operating at 300kV. The interlamellar spacing was determined using TEM micrographs by measuring the consecutive distance between ferrite lamella and cementite lamella. After stereographic correction, the true interlamellar spacing is reported in Table 1. The colony size was determined using SEM micrographs by measuring the dimensions of the regions where the cementite lamellae were oriented in a particular direction parallel to one another. To calculate the pearlitic nodule size, EBSD imaging was done over an area of 100 μm×100 μm with a step size of 0.05 μm to determine regions in the microstructure where the ferrite misorientation was less than 13° (Taleff et al., 2002). The fracture surface imaging was done using a JEOL-IT800 dual vacuum high-resolution scanning electron microscope (HR-SEM). The true inter lamellar spacing, colony size, and nodule size measurements are listed in Table 1. The crack propagation profile is critical to investigate as a function of temperature and microstructure. Hence, SEM imaging was done on a plane perpendicular to the crack growth plane in regions just below the crack after nickel coating of the fracture surface. 3. Results and Discussion Fig 1: (a) TEM image of NP550 showing interlamellar spacing (b-c) SEM image of NP550 showing lamellar structure and colony size of pearlitic steel (d-f) EBSD image and nodule size measurement for NP550. represents the TEM and SEM micrographs for the pearlitic steel isothermally transformed at 550 ° C. The heat treatment at 550 ° C resulted in a complete pearlitic microstructure as seen in Fig 1 (a-c). The low-temperature transformation was made possible because of the high content of Mn in the steel, which decreases the bainitic start temperature. Fig 1: (a) TEM image of NP550 showing interlamellar spacing (b-c) SEM image of NP550 showing lamellar structure and colony size of pearlitic steel (d-f) EBSD image and nodule size measurement for NP550., colony size was measured for the regions having cementite lamella parallel to each other. Fig 1: (a) TEM image of NP550 showing interlamellar spacing (b-c) SEM image of NP550 showing lamellar structure and colony size of pearlitic steel (d-f) EBSD image and nodule size measurement for NP550., represents the EBSD micrographs. The region size versus the area fraction of the region having ferrite with misorientation less than 13° is evaluated through the EBSD micrograph and shown in Fig 1: (a) TEM image of NP550 showing interlamellar spacing (b-c) SEM image of NP550 showing lamellar structure and colony size of pearlitic steel (d-f) EBSD image and nodule size measurement for NP550.. The measured interlamellar spacing, colony size, and nodule size are shown in Table 1.