PSI - Issue 37

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E. Entezari et al. / Procedia Structural Integrity 37 (2022) 145–152 E.Entezari et al./ Structural Integrity Procedia 00 (2021) 000 – 000

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Fig. 3. Optical and SEM micrographs of samples quenched at a and b) 260 °C, c, and d) 280 °C, e, and f) 300 °C.

Table 1. The results obtained from the thickness measurement of bainitic plates. Sample Average thickness of bainitic- ferrite subunits (μm) Quenched at 260 °C 0.162 Quenched at 280 °C 0.193 Quenched at 300 °C 0.253

Table 2 shows the tensile properties of the Q-P treated samples extracted from stress-strain curves (Fig. 4). It is observed that the steel sample quenched at 260 °C has the maximum tensile strength of 1415 MPa and elongation of 16 %, whereas the tensile strength of the samples quenched at 280 and 300 °C reduced to 1398 (-1.2%) and 1385 MPa (-1.2%), respectively, whereas the changes in elongation were similar (+1.25%). The observed combination of tensile properties can be attributed to the mixture strengthening mechanism due to the increment in the volume fraction of austenite/martensite microblocks, tempered martensite, and the thickness of bainitic plates. The volume fraction of austenite/martensite microblocks in steel samples is increased during Q-P treatment, in agreement with the work of Kocatepe et al. (2006). Furthermore, the presence of tempered martensite was effective in improving the strength of Q-P treated samples by a fine particle strengthening mechanism, as expressed by Lee et al. (2019).