PSI - Issue 37

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

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E.Entezari et al. / Structural Integrity Procedia 00 (2021) 000 – 000

Besides the austenite/martensite microblocks and tempered martensite, the thinner bainitic sheaves increased ultimate tensile strength by refining the microstructure, from the results of Langford-Cohen (1969).

Table 2. Tensile properties of Q-P treated samples. Sample UTS (Mpa)

EL (%)

Quenched at 260 °C Quenched at 280 °C Quenched at 300 °C

1415 1398 1385

16 17 18

Fig.4. Stress-strain curves of Q-P treated samples.

The Charpy impact test results at room temperature for all investigated samples are summarized in the table. 3. The results indicate that decreasing quenching temperature during Q-P enhanced the impact energy of the studied samples up to 14.3%. This result is attributed to the slender bainitic sheaves with various crystallographic orientations and tempered martensite in accordance with the findings of Avishan et al. (2012) and González-Velázquez (2019).

Table 3. Charpy impact energy of the Q-P treated samples. Sample

Charpy impact energy (±4 J)

Quenched at 260 °C Quenched at 280 °C Quenched at 300 °C

42 38 36

Fig. 5 shows the SEM views of the fracture surfaces of tensile test and Charpy impact test samples subjected to the Q-P treatment at different quenching temperatures. It can be seen that the fracture surfaces of tensile test specimens consisted of a combination of shallow and deep ductile rupture dimples, whereas the Charpy impact test specimens showed a combination of cleavage facets and shallow ductile rupture dimples. It is clear that the ductile fracture dimples are formed in the retained austenite regions, whereas the cleavage component of the fracture appears in the low ductility constituents such as martensite and bainite.