PSI - Issue 60

P.K. Sharma et al. / Procedia Structural Integrity 60 (2024) 335–344 P.K. Sharma/ Structural Integrity Procedia 00 (2023) 000 – 000

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of Alloy 690 material using single edged notched tensile (SENT) specimen in the temperature range of 25- 1000˚C. SENT specimen was chosen due to its lesser crack tip constraints (Zhu 2015 and Ekabote et al. 2020) that can simulate the propagation of micro-cracks developed during operation of different components of Alloy 690 material. 2. Design, fabrication of the fracture specimen and description of experimental procedure For the fracture specimen, specimen has been machined from 10 mm thick hot-rolled plates of Alloy 690 material as shown in Fig. 1(b). The material was obtained from WIP, BARC. Chemical composition of Alloy 690 material was found out using ASTM E 3047:2016. Final composition used for fabrication of specimen is shown in Table 1.

Table 1: Chemical composition of alloy 690 used for the test. S.No. Elements

Typical Range (in %)

Actual %

1 2 3 4 5 6 7 8

Nickel

58.0 (Minimum)

62.67 28.21 8.192 0.024 0.209 0.252 0.003 0.162

Chromium

28-31

Iron

7-11

Carbon Silicon

0.4 (Maximum)

0.2-0.5 0.2-0.5

Manganese

Sulphur Copper

0.002-0.004

0.5(Maximum)

Single edged notched tensile (SENT) specimen have been designed for evaluating the fracture toughness of Alloy 690 material. This type of specimen was chosen to simulate the lower crack-tip constraint conditions observed in the components of vitrification melters due to presence of micro-cracks. Thickness of the specimen is around 3.25 mm, i.e., 3 specimens were obtained from a 10 mm thick plate used for specimen fabrication. Height of the specimen is 100 mm whereas width is taken as 25 mm as shown in Fig. 1(a). Crack length before fatigue pre-crack of the specimen is 12 mm. Later, the specimen is fatigue pre-cracked using the standard ASTM procedure and the crack length becomes 12.5 mm after pre-cracking and it is denoted as initial crack length a 0 .

(a) (b) Fig. 1: (a) Geometrical details of the SENT specimen (all dimensions are in mm); (b) SENT specimen used for the fracture testing. 2.1. Test matrix, fatigue pre-cracking details and fracture surface examination after test The test matrix used for determination of fracture toughness of Alloy 690 material is shown in Table 2. Four tests have been carried out with minimum two tests at a particular temperature to check the repeatability of test. Tests have been conducted in the temperature range of 25 to 1000˚C. Specimen temperature has been measured using standard k-type thermocouple which has an accuracy of ±2 ˚ C or ±0.3% (whichever is lesser). The thermocouple and temperature controller were well calibrated before the actual tests were carried out. The temperature range of 25 1000 ˚ C is chosen as this falls in the operating range of components of vitrification melters. Single specimen technique has been used in the fracture test. Unloading compliance technique has been used for evaluation of crack growth. The fracture tests have been carried out on a universal testing machine of 30 kN load capacity and a high temperature furnace capable of reaching upto 1200˚C. Tests were carried out at quasi-static loading rates using displacement