A Study of the Effect of Aging on Uniaxial Tensile Deformation and Fracture Resistance of SS 316 LN Welds

Effect of aging (370-550 °C, 1000-20,000 h duration) on crack tip opening displacement (CTOD) of SS 316 LN welds at room temperature (RT), 380 and 550 °C is investigated. Decrease in both % Total elongation and CTOD fracture toughness (δ1c) after 20,000 h aging duration (all aging temperatures) was observed. Fracture results are explained based on changes in microstructure. Determined CTOD (δ1c) along with tensile properties are considered for estimation of fracture toughness (K1C) and based on three different models. Both parameters CTOD and K1C are considered for fracture toughness estimation. Estimated K1C results are compared to the determined KJ1C (equivalent linear elastic) values. In first model, Modulus of toughness (SED) and Youngs Modulus are considered. In second model, yield stress, Youngs Modulus and fracture strain are considered. The second model is applied for SS 316LN and similar type of welds. A third model was considered to estimate K1C from determined CTOD (δ1c) along with tensile properties. On application of three models, it is observed that error in estimated K1C results was in the range (10-29)%. Based on estimated results, it is summarized that previous three models to estimate K1C are applicable for SS 316 type of welds.