Characterisation of Fatigue Crack Growth and Fracture Behaviour of SS 316L(N) Base and Weld Materials

Abstract

This paper summarizes the results of the studies on fracture mechanics characterisation of SS 316L(N) and its welds. The results presented include the fracture toughness and FCG properties of the base and weld materials at different temperatures. Influence of nitrogen content on the base material properties is discussed. Further, the effects of long-term ageing at different temperatures on the fracture and FCG behaviour of the welds are presented and discussed. The weld metal has been subjected to extended thermal ageing, and a detailed study has been undertaken to characterize the (i) FCG properties and (ii) quasistaticJ-R curves for the indigenously developed SS 316(N) weld material at both ambient and service temperatures. The ageing conditions covered include the advanced ageing according to the RCC-MR design code, i.e, > 4000 h at 923 K and the low temperature ageing, i.e., 643-823 K the operating range for the SS 316L(N) components in PFBR. The results are discussed in detail in the light of microstructural changes taking place in the weld metal and their influence on the operating micromechanisms.