PSI - Issue 41

6

Abdelmoumene Guedri et al. / Procedia Structural Integrity 41 (2022) 564–575 Abdelmoum ne Gu dri et al. / Structural Integrity Procedia 00 (2022) 00 –000

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Fig 5: Evolution of the area at the break deformation as a function of temperature and strain rate.

This ductility decrease observed at 800 °C is attributed to the formation of a thin primary ferrite film, observed on the micrographs Figures 6 to 7 following the precipitation treatment and causing a concentration of the deformation in the vicinity of the joints grains. On the other hand, at 750°C the ferrite film is wider and by a relaxation effect of the concentration of the deformation, improves the ductility.

Fig.6. M. E. B from a sample deformed at 800 ° C.

The presence of the second zone of ductility variation which is in the austenitic domain (at 900 ° C) near the two phase domain can be explained by the process proposed by Portevin (1970) and taken up by Trombert (1988). At temperatures between 850°C and 1050°C, it is known that in the absence of additive elements, the austenitic phase has good ductility. In the case of our material and following the precipitation treatment, it is observed that in the austenitic field from 950 ° C, the ductility stabilizes or increases slightly reaching high values, i.e., Z (%) = 94%. If we refer to the thesis work (Ping-Hua, 1989), this improvement in ductility and state of stress would be explained by the presence of dynamic recrystallization. The dissolution of the precipitates at high temperature or the weak