PSI - Issue 71

Pramod Ravindra Kushwaha et al. / Procedia Structural Integrity 71 (2025) 74–81

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cylindrical types carbide precipitates were observed within the grains (Zhao et al. 2001). Grain-boundary (GB) precipitates were predominantly M 23 C 6 , with a minor presence of MC. In the microstructure of Su-263 the annealing twins can be seen in multiple grains.

a

b

Twins

Fig. 3. (a) Optical micrograph and (b) Scanning electron micrograph of as received Su-263

4.2 SPC results The test parameters like temperature and load for SPC test were decided on the basis of service condition for the Su 263 samples. The small punch creep tests were performed at constant 650 °C temperature and three loads 650 N, 700 N and 750 N as mentioned in the Table 2. Creep properties like time of rupture (hr.) and creep rate (mm/hr.) for the test condition are also shown. Based on the results from the multiple tests it was observed that the creep life (time of rupture in hr.) decreased as the load increased and was seen in punch displacement versus time graph, Fig. 4 (a). The average creep life of Su-263 was found to be 88.20 ± 1.50 hrs, 50.10 ± 1.50 hrs and 36.15 ± 1.50 hrs at 650 N, 700 N, and at 750 N, respectively. There is significant decrease in creep life of 42.5% during increases in load levels from 650 N to 700 N and 28.7% from 700 N to 750 N and overall, 59.0% from 650 N to 750 N was seen on increasing the load. Creep rate curves for all the Su-263 samples are shown in Fig. 4 (b). It can be observed that at constant temperature with increasing load, the minimum creep rate goes on increasing.

(a)

(b)

Fig. 4. (a) Punch displacement curve (b) creep rate for loads 650 N, 700 N and 750 N at 650 °C From Fig. 4, it was observed that the creep behaviour in SPC was similar to that in conventional creep, where the creep rate decreased during the primary stage, reached a minimum, and then increased in the tertiary stage until the sample fractured. In the graphs, it can be seen that the behaviour was similar in all the tests and shows peak after 16 hrs which resembled hump of the punch displacement curve shown in Fig. 4 (a).