13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Figure 7 SEM micrograph of creep specimen near the fracture, (a). 700°C/240MPa, 1085h, transgranular cracking, (b). 700°C/210 MPa, 4203h, transgranular and intergranular mixed model, (c). 700°C/150 MPa, 14040 h, intergranular cracking Plastic deformation and transgranular fracture is the main creep fracture mechanism in UNS S31035 material in the temperature ranges of interest (<700°C). The SEM analysis shows that the crack initiation area was mainly quasi cleavage and then cracks propagated with dimples. At intermediate stresses and temperatures a mixture of inter- and transgranular fracture occurs. The crack initiation often occurs at grain boundaries but propagate through the grains. At relatively low stresses and high temperatures, intergranular fracture could occur. However, plastic deformation can still be observed in these specimens. Figure 8 Fracture modes in UNS S31035 at different test conditions. 4. Conclusions A new austenitic stainless steel grade, UNS S31035 (Sandvik Sanicro 25), has been developed intended for superheater and reheaters for A-USC. Extrapolation from creep data with two methods gives a creep strength of 99 ± 3 MPa at 700°C for 100 000 h, which is higher than that of other austenitic stainless steels available today. (a) (c) (b) (a) (b)
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