Issue 48

S.C.S.P. Kumar Krovvidi et alii, Frattura ed Integrità Strutturale, 48 (2019) 577-584; DOI: 10.3221/IGF-ESIS.48.56 579 fatigue testing system. The creep-fatigue interaction test was also conducted at total strain amplitude of ± 0.4 % with 1 minute hold at peak tensile strain. Element C Mn Si Ni Ti Cr Mo S P Fe wt.% 0.018 1.89 0.27 10.81 0.19 16.9 2.14 0.001 0.04 Bal. Table 1 : Chemical composition of 316Ti stainless steel (wt. %) Figure 2 : The schematic of specimen used for LCF and CFI testing. R ESULTS AND DISCUSSION ensile test was carried out at 823 K and at a strain rate of 3×10 -3 s -1 . The engineering stress-strain curve obtained from the tensile test is shown in Fig. 3. The tensile properties evaluated for the steel are given in Tab. 2. Dynamic strain ageing (DSA) during tensile deformation is generally manifested as serrated yielding in the stress– strain curve, Fig. 1. The DSA occurs at certain strain rate and temperature ranges and is a characteristic of the material and its microstructure [12]. Generally, the DSA occurs due to the interaction between solute atoms and dislocations at temperature where the mobility of solute is sufficient to lock mobile dislocations [13]. The serrations in the tensile curve or hysteresis loops in fatigue associated with the repeated locking and unlocking of dislocations in solute atmospheres. Ganesan et al. studied the effect of nitrogen on DSA behaviour of 316 LN SS during tensile test [13]. Serrated flow was observed in the stress-strain curve for tensile tests in the intermediate temperature range of 773–973 K. Figure 3 : The engineering stress-strain curve of the steel obtained from tensile test at 823 K. Elastic modulus, MPa Yield stress, MPa Ultimate tensile strength, MPa Uniform elongation, % Total elongation, % 154000 151 394 25.8 32.1 Table 2 : Tensile properties of the material at 823 K T