PSI - Issue 60

B Shashank Dutt et al. / Procedia Structural Integrity 60 (2024) 471–483 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

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1. Introduction SS 316LN is the material used for many structural components of prototype fast breeder reactor. Many of these components are subjected to operating temperatures in the range 370 to 550 °C. For fabrication of these components, welding is a major manufacturing process. The welded components on exposure to various operating conditions undergo aging, resulting in degradation of fracture resistance ( J -R curves) and fracture toughness ( J 1c ). Effect of aging on mechanical properties austenitic stainless steel welds has been previously investigated (Chandra et al. 2012; Kumar et al. 2020; Hong et al. 2015; Vitek et al. 1991). The authors (Dutt et al. 2011; Dutt et al. 2018) and other investigators (Sasikala and Ray 2011) have previously studied effect of aging on the fracture toughness of SS 316 LN welds. Hong et al.(2018), investigated effect of aging on tensile properties and fracture resistance of austenitic stainless steel welds. Yu et al. (2018), evaluated fracture toughness of cast stainless steel welds at different locations of the weld joint. In addition to experimental methods, some attempts have previously been made to predict fracture toughness ( J 1c ) and J -R curves of SS 316L welds (Youn et al. 2021). In previous study by Youn et al. (2021), three different models were considered to estimate J -R curves and J 1c of 316L welds. The previous models were applied for cast stainless steels. In previous models, estimation of fracture toughness was carried out based on various empirical equations. In previous models, determined Charpy impact energy values of cast stainless steels, subjected to various time Temperature aging conditions and for varying compositions were considered. In a subsequent investigation by Kim et al. (2022), a different estimation method was used to predict fracture toughness and J -R curves of thermally aged 316L stainless steel welds. For estimation of fracture resistance, various closed form expressions based on aging constants were considered along with tensile properties. In this investigation, a different methodology is considered for estimation of fracture resistance ( K 1c ). In a previous study by Baskes (1975), an empirical equation was proposed for estimation of K 1c from tensile properties. In a later investigation by Oh (2022), K 1c was estimated by considering tensile properties and Charpy impact energy of various types of steels. In this investigation, an attempt was made to estimate K 1c from tensile properties and based on model proposed by Baskes (1975). The following are the objectives of this study. To estimate fracture resistance ( K 1c ) of SS 316 LN welds, based on tensile properties. The tensile properties of the welds were determined at various aging conditions (370-550 °C, 1000-20,000 h durations) and test temperatures in the range RT-550 °C. The differences between estimated K 1c and determined fracture toughness ( K j1c ) values are reported. The second objective is to apply K 1c estimation for similar class of austenitic stainless steel welds (Hong et al. 2018), subjected to aging at 400 °C (maximum 10,000 h durations) and tested at 25 and 320 °C. The additional objective of this study is to apply K 1c estimation for cast stainless steel welds, tested at different locations of the weld joints and tested at room temperature (Yu et al. 2018). The experimental details are discussed in subsequent paragraphs. 2. Experimental The composition of SS 316 LN (base metal) is mentioned in table 1. The stainless steel was previously supplied in the form of plate having 30 mm thickness and in the mill annealed condition. From the plate, weld pads were prepared by shielded metal arc welding process. It was verified that weld pads are defect free by radiographic inspection. From the weld pads, specimen blanks were fabricated ensuring that notch is placed such that crack growth is along the welding direction. The fabricated weld pads were of dimensions 75 mm length, 70 mm width and 30 mm thickness. These weld blanks were subjected to various aging conditions as mentioned in table 2. From the aged blanks, tensile (cylindrical) specimens were fabricated having 28 mm gauge length and 4 mm gauge diameter. The gauge length of the tensile specimen was along the welding direction and parallel to the rolling direction of the plate. The fabricated tensile specimens had gauge length greater than four times the gauge diameter. Tensile testing was carried out using a screw-driven testing machine and at a strain rate of ~ 2×10 -4 s -1 . The temperature during testing was controlled within ± 2 °C. The tensile specimens were tested at temperatures of RT (room temperature), 380 and 550 °C, for all the aged and unaged weld specimens. The average tensile test result for all the test temperatures were reported by testing 3 numbers of specimens for every test temperature. From the aged