Study of creep crack growth behaviour of a type 316(N) stainless steel weld and its mechanism

As the high temperature structural integrity of the welded components is often decided by the extent of crack growth in the weld itself, the evaluation of the creep crack growth (CCG) rate and its micromechanical characterization in the welds are of importance to the designers. This study presents the CCG characterization of a type 316(N) stainless steel (SS) weld containing about 5 FN (ferrite number) of delta-ferrite. Constant load CCG tests using compact tension (CT) specimens have been carried out in the temperature range of 823-923 K as per ASTM E1457-15. The creep crack growth rate (ȧ) vs. C* [ȧ-C*] plots, commonly expressed as ȧ=D(C*)φ, were established and compared in the temperature range of 823-923 K. The SEM/ EBSD analysis, carried out in the vicinity of the crack propagation path, has revealed inter-granular nature of creep crack propagation. This is attributed to the grain boundary σ-phase precipitations, which were found to be coarser as compared to the σ-phase precipitations in the grain interiors, leading to easier damage accumulation and microcrack formation in their vicinity.