PSI - Issue 41

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

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at the break deformation which is between 0.6 and 0.5. This trend is observed at all temperatures except at 750°C. At this temperature, we notice the absence of a bearing with a stress of 140 MPa. The rate of deformation at break is low at maximum peak compared to other temperatures, being around 0.4.

Figure. 10. Evolution of the flow stress as a function of temperature for the strain rate 1.96x10 -3 s -1 . These behaviors are usually described by dynamic restoration. These observations suggest that the presence of additive elements such as Ti, Nb, V and Al combined with nitrogen favor the following effects:  Delay or slowdown of dynamic recrystallization. This manifests itself, on the one hand, by an increase in the rate of deformation at the break deformation and a "smooth" appearance of the stress-strain curves;  Hardening of the material which manifests itself by increasing the flow stress. This typical behavior is also observed at strain rates equal to 9.8 x 10 -3 s -1 and 4.9 x 10 -4 s -1 as shown in Figure 11. In fact, the precipitation treatments favor an increase in the resistance tensile strength and rate of deformation at the break deformation for all temperatures except 750°C, at which temperature the material behaves differently. At this temperature 750°C which corresponds to the beginning of the two-phase domain the deformation acts on a ferritic dominated structure, and the influence of the heat treatment before deformation remains insufficient to cause a clear difference in the mechanical properties.

Fig. 11. Evolution of the flow stress as a function of temperature (strain rate: 4.9x10 -3 s -1 and 9.8x10 -3 s -1 ).