13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- with a few serration drops at 22% strain at 700°C. At room temperature the elongation to fracture increases with decreasing strain rate for AISI 316L, at a strain rate of 2*10-3/s it is 53% and 66% at 10-6/s, see fig.1b). This behaviour is due to the lower deformation rate that causes the dislocation mobility to decrease and therefore resulting in a lower stress level when using a strain rate of 10-6/s. At elevated temperatures and low strain rates AISI 316L show a decrease in the stress-level during tensile tests due to recovery that could be related to recovery-creep [11], see fig.1b), also features related to dynamic recrystallization can be found in the microstructure (fig.4) [12]. The strain rate influences the ductile response of Alloy 617, as shown in fig. 2 a). From 10-2/s to 103/s the ductility increases at both temperatures and continues to increase for strain rates of 10-4/s at 650°C but decrease slightly at 700°C. With even slower strain rates the ductility decreases even more for both temperatures, 700°C have lower ductility than 650°C at a strain rate of 10-6/s but have a higher tensile stress which can explain the differences in ductility. Alloy 617 has much higher ductility (ART=70.5%) and tensile stress (RmRT=709MPa) when it is deformed at room temperature than at elevated temperature (A700°C=10.3% and Rm700°C=489MPa) when using a strain of rate 10 - 6/s, see fig.2. This behaviour is most likely due to grain boundary embrittlement coused by chromium rich precipitation in the grain boundaries, shown in fig.6. In the DSA regime nano-twins can show up as a deformation mechanism [13]. AISI 316L material showed nano-twins close to the surface of the specimen. Other deformation mechanism in the microstructure of the SSRT tested samples was slip bands (SB) and planar slip. Fig.3 displays probable future damage due to interaction between slip bands and precipitates (fig.3 b)) and nanotwins and precipitates. Contrast differences that could be related to stress concentrations spots which is or will be future damage can be observed where these interactions appear in fig. 3 b) and c).
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