13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Figure 1. Fine precipitates that contribute to the creep strength of austenitic stainless steel grade, UNS S31035, (a) M23C6, 700°C for 1000 hours, (b) Laves phase, 700°C for 30 000 hours, (c) Copper-rich phase, 700°C for 30 000 hours, (d) Nanoparticles, 700°C for 30 000 hours. The creep testing on UNS S31035 was performed from 550°C to 800°C. Both stress-rupture testing and creep-strain testing were done. The stress-rupture testing was performed in Escher Wyss (EW) creep testing machines. In these machines multiple samples can be tested simultaneously. The samples (Fig. 2) are mounted in the EW boxes. The tube in which the samples are located is then inserted into the furnace. The load from the compressed spring is applied after the samples have been heated in the furnace for one hour. The creep-strain testing was performed in Bofors machines. The sample was mounted in sample holders in the tube furnace and connected to thermocouples which can measure the temperature continuously. The strain was measured by two extensometers placed outside the furnace. The strain was logged manually regularly during testing to obtain creep curves. Figure 2. Schematic sample for the creep test. The microstructure was studied using light optical microscope (LOM), scanning electron microscope (SEM) and transmission electron microscope (TEM). LOM and SEM were used to obtain information on features such as grain size, creep deformation, precipitates and how these changes with time, temperature and stress. TEM was used for phase identification and dislocation structure characterization. (d) (c)
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