PSI - Issue 68

Bhawesh Chhajed et al. / Procedia Structural Integrity 68 (2025) 708–714 Bhawesh Chhajed et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig 5 (a) Bright field image for NSB_350 captured using TEM in the region corresponding to stage II of FCGR test; (b) SAED of the corresponding bright field image; (c) Dark field image corresponding to the spot marked by white arrow; (d) another region observed using TEM showing the twin formation in austenite; (e) corresponding SAED pattern of the twinned austenite; (f) Dark field image corresponding to spot marked using white arrow

Fig 6 BF TEM image captured in NSB_350 FCGR tested specimen along with corresponding SAED pattern showing indexed α/α’ phase

Fig 7 HRTEM image captured for austenite in NSB_350 FCGR tested specimen in Paris Law regime and corresponding Fourier transform (FT) EDP of the region marked by blue dotted boundary

4. Conclusions Steel austenitised at 950°C for 40 min was austempered at 350°C and 250°C for 20 and 40 hrs respectively to obtain nano-structured bainite. Both heat-treated specimens were subjected to FCGR test in an earlier study by Kumar and Singh (2019) and the deformed specimens extracted from the Paris Law regime were studied using TEM in the current study. The following conclusions can be drawn: 1. NSB_350 displays martensitic transformation in the Paris law regime along with the formation of deformation twins in retained austenite.